Dissertations / Theses on the topic 'Dendritic materials'

Electroactive organic materials have been making progress towards technological applications such as organic light-emitting diodes (OLEDs). In particular, use of electroluminescent dendritic materials in OLEDs show significant promise for a wide range of practical requirements because of their macromolecular structure being highly controllable with regard to both the chemical and physical properties. This thesis describes the development of synthetic approaches to novel phosphorescent dendrimers containing either 1,3,S-triazine or benzimidazole dendrons with the aim to develop materials in which the high electron affinity of the dendrons would be higher than the core and hence facilit~te electron transport through emissive layers in OLEDs. At an early stage, significant difficulties in the stability of triazine derivatives were identified, requiring an introduction of stabilising groups onto triazine rings. With analysis of reactivity and stability of 1,3,S-triazine derivatives, a promising structural modification of using carbzolyl moieties attached to triazine-branching units was discovered. It was found that triazine-based dendronised ligands could not be complexed to iridium(III) to give a single compound due to multiple co-ordination sites. The introduction of an amine linker solved this problem with the dendrons being added to the already fonned complex. 2-Ethylhexyloxy surface groupS were found to increase the solubility of the dendrimers in common organic solvents and also decreased intermolecular interactions of the emissive cores. Dendrimers with benzimidazolyl units in the dendrons were also prepared. that the redox processes were also dendron-dependent. Molecular orbital calculations quantum yield was dependent on the dendron type. Electrochemical analysis showed The photophysical properties of the dendrimers showed that the photoluminescence of the orbital energies and distribution were consistent with the observed properties. containing a light-emitting dendrimer comprised of the dendrimer 114 blended with Finally, OLED devices were fabricated using the soluble dendrimers. The highest external quantum efficiency of 5.4% at 100 cdlcm2 was observed for a bilayer device 4,4'_bis(N-carbazolyl)biphenyl (CBP) as a host.

Thesis (Ph. D.)--Dept. of Chemistry and School of Pharmacy. University of Missouri--Kansas City, 2007.
"A dissertation in chemistry and pharmaceutical science." Advisor: Zhonghua Peng. Typescript. Vita. Description based on contents viewed Apr. 22, 2008; title from "catalog record" of the print edition. Includes bibliographical references (leaves 160-176). Online version of the print edition.

Förfrågan efter nya och mer avancerade applikationer är en pågående process vilket leder till en konstant utveckling av nya material. För att förstå relationen mellan en applikations egenskaper och dess sammansättning krävs full förståelse och kontroll över materialets uppbyggnad. En sådan kontroll över uppbyggnaden hos material hittas i en undergrupp till dendritiska polymerer som kallas dendrimerer. I den här doktorsavhandlingen belyses nya metoder för att framställa dendrimer med hjälp av selektiva kemiska reaktioner. Sådana selektiva reaktioner kan hittas inom konceptet klickkemi och har i detta arbete kombinerats med traditionell anhydrid- och karbodiimidmedierad kemi. Denna avhandling diskuterar en accelererad tillväxtmetod, dendrimerer med inre och yttre reaktiva grupper, simultana reaktioner och applikationer baserade på dessa dendritiska material. En accelererad tillväxtmetod har utvecklats baserad på AB2- och CD2-monomerer. Dessa monomerer tillåter tillväxt av dendrimerer utan att använda sig av skyddsgruppkemi eller aktivering av ändgrupper. Detta gjordes genom att kombinera kemoselektiviteten hos klickkemi tillsammans med traditionell syraklorid kopplingar. Dendrimerer med inre alkyn- eller azidfunktionalitet syntetiserades genom att använda AB2C-monomerer. Den dendritiska tillväxten skedde med hjälp av karbodiimidmedierad kemi. Monomererna som användes bär på en C-funktionalitet, alkyn eller azid, och på så sätt byggs får interiören i de syntetiserade dendrimeren en inneburen aktiv funktionell grupp. Ortogonaliteten hos klickkemi användes för att sammanfoga monomerer till en dendritisk struktur. Traditionell anhydridkemi- och klickemireaktioner utfördes samtidigt och på så sätt kunde dendritiska strukturer erhållas med färre antal uppreningssteg. En ljusemitterande dendrimer syntetiserades genom att koppla azidfunktionella dendroner till en alkynfunktionell cyclenkärna. Europiumjoner inkorporerades i kärnan varpå dendrimerens fotofysiska egenskaper analyserades. Mätningarna visade att den bildade triazolen hade en sensibiliserande effekt på europiumjonen. Termiska studier på några av de syntetiserade dendrimerer utfördes för att se om några av dem kunde fungera som templat vid framställning av isoporösa filmer.
The need for new improved materials in cutting edge applications is constantly inspiring researchers to developing novel advanced macromolecular structures. A research area within advanced and complex macromolecular structures is dendrimers and their synthesis. Dendrimers consist of highly dense and branched structures that have promising properties suitable for biomedical and electrical applications and as templating materials. Dendrimers provide full control over the structure and property relationship since they are synthesized with unprecedented control over each reaction step. In this doctoral thesis, new methodologies for dendrimer synthesis are based on the concept of click chemistry in combination with traditional chemical reactions for dendrimer synthesis. This thesis discusses an accelerated growth approach, dendrimers with internal functionality, concurrent reactions and their applications. An accelerated growth approach for dendrimers was developed based on AB2- and CD2-monomers. These allow dendritic growth without the use of activation or deprotection of the peripheral end-groups. This was achieved by combining the chemoselective nature of click chemistry and traditional acid chloride reactions. Dendrimers with internal azide/alkyne functionality were prepared by adding AB2C monomers to a multifunctional core. Dendritic growth was obtained by employing carbodiimide mediated chemistry. The monomers carry a pendant C-functionality (alkyne or azide) that remains available in the dendritic interior resulting in dendrimers with internal and peripheral functionalities. The orthogonal nature of click chemistry was utilized for the simultaneous assembly of monomers into dendritic structures. Traditional anhydride chemistry and click chemistry were carried out concurrently to obtain dendritic structures. This procedure allows synthesis of dendritic structures using fewer purification steps. Thermal analyses on selected dendrimers were carried out to verify their use as templates for the formation of honeycomb membranes. Additionally, a light emitting dendrimer was prepared by coupling of azide functional dendrons to an alkyne functional cyclen core. A Europium ion was incorporated into the dendrimer core, and photophysical measurements on the metal containing dendrimer revealed that the formed triazole linkage possesses a sensitizing effect.
QC 20100629

This dissertation investigates the synthesis and analysis of new dendritic compounds for their utility as nonlinear optical materials. Two-photon absorbing dendritic dyes and octasubstituted dendritic phthalocyanines utilize the dendrons along the periphery in order to shield the central, "active" core from the external environment. An attempt to obtain phthalocyanine materials for use as optical limiters entailed the attachment of dendritic substituents through a hydroquinone spacer to phthalonitriles which were then cyclized to give the target phthalocyanines. Investigation of the aggregation properties of these compounds showed that as the generation of the dendritic substituent increased, the amount of aggregation decreased. This was seen both in thin films as well as in solution. However, as the dielectric constant of the solvent increased, aggregation of individual phthalocyanines in solution also increased. Substitution on the periphery of the dendron also had a role in how the phthalocyanine behaved in solution. The presence of t-butyl groups in the meta positions along the periphery of the dendrimer further decreased the amount of aggregation that occurred in solution. The addition of zinc to the core of the phthalocyanine led to further prevention of aggregation, again in both thin films and in solution. Fluorescence studies on these compounds had indicated the presence of an energy transfer mechanism between the dendron periphery and the phthalocyanine core. The dendritic zinc phthalocyanines also displayed small KSV values which suggest that the approach of quenching molecules to the core of the phthalocyanine is greatly hindered in solution by the dendritic periphery. In the development of a material for biomedical imaging, a strong effect was exhibited by the change in polarity of the solvent on the two-photon absorption (TPA) of bis-styrylbenzene (BSB) dyes which resulted in a loss of the fluorescence quantum yield (phif) as the polarity increased. Covalent attachment of different generations of a 4-carboxy terminated dendron to the dye resulted in a smaller decrease in the phif based upon the generation of the attached dendron. A study of the solvent effect on the dicyano-substituted BSB dendritic TPA dye indicated the presence of a possible hydrogen bonding interaction between the dendron and the dye at low pH. This interaction resulted in a strong decrease in the phif of the dye, a loss that was partially remedied by raising the pH to 12.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.
Includes bibliographical references.
Dendrimers are three-dimensional, hyperbranched macromolecules that possess a uniform size and shape. Most dendrimers are spherical in shape; however, the shape of the dendrimer can be adjusting using the number and the position of the branching groups in the core. For example, dendritic rods have been prepared by assembling a dendron around each repeat unit of a linear polymer core, and hybrid-linear dendritic diblock copolymers have been prepared by attaching a dendron to the end functional group of a linear polymer. This linear block in the diblock copolymers also adds physical integrity and an assembly mechanism for arrangement of the polymer. Nonetheless, no one has combined the unique shape of the dendritic rod with that of the linear dendritic diblock copolymer. The objective of this research was to prepare a linear-dendritic rod diblock copolymer, and to examine its assembly behavior in solution, at the air/water interface, and in the bulk. These polymers consisted of a linear poly(ethylene oxide)-poly(ethylene imine) diblock copolymer around which poly(amido amine) branches were divergently synthesized. The dendritic branches were terminated with amine and ester groups, as well as alkyl chains of various lengths in order to "tune" the amphiphilic nature of the polymer.
(cont.) A fundamental change in the assembly behavior of the polymers was observed at generation 4.0 (eight end-groups). In solution, the hydrodynamic and viscometric radii were found to increase to a much greater extent than expected for the generation 4.0 and 4.5 polymers, consistent with a breakdown of the spherical approximation as the dendritic block extended into a rod-like shape. Similarly, at the air/water interface, the dendritic block of generation 4.0-alkyl terminated polymers all adopted a horizontal rod configuration, while the dendritic block of the lower generation polymers took on a random coil configuration, whose shape depended on the length of the terminal alkyl groups as well as the generation number of the dendritic block. Finally, in the bulk, direct observation of the generation 4.0-dodecyl terminated polymer with TEM indicated that the polymer was adopting a rod- or worm-like conformation, while the lower generation polymers only exhibited traditional diblock copolymer or polymer brush behavior.
by Catherine Marie Bambenek Santini.
Ph.D.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xix, 343 p.; also includes graphics (some col.) Includes bibliographical references (p. 325-343).

Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2007.
Committee Chair: Julia Babensee ; Committee Members: Barbara Boyan, John Brash, Andres Garcia, and Niren Murthy. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
Includes bibliographical references (leaves 66-69).
Cancer immunotherapy attempts to stimulate the immune system to reject and destroy tumor cells. Despite the amount of ongoing intensive research to prevent cancer, tumor cells continue to evade immune responses. Currently, dendritic cell vaccines are in development, in which autologous antigen-loaded dendritic cells are injected back into the patient in order to generate an appropriate immune response. Improving upon this idea, members of the Irvine laboratory are in development of an injectable dendritic cell based formulation that gels in situ around the tumor site. In this way, immune cells (most notably T cells) can be recruited and become activated against specific tumor antigens, and (hopefully) kill tumor cells. Recent studies have shown the potential benefit of incorporation of cytokine interleukin-15 complexed with its soluble receptor interleukin-5R[alpha], which is discussed. Economic considerations are also discussed, including topics such as intellectual property, barriers to entry, initial markets and market drivers, and entry into the current supply chain considerations. A business strategy is outlined and evaluated.
by Andrew Song.
M.Eng.

Advancements in the biomedical field are driven by the design of novel materials with controlled physical and bio-interactive properties. To develop such materials, researchers rely on the use of highly efficient reactions for the assembly of advanced polymeric scaffolds that meet the demands of a functional biomaterial. In this thesis two main strategies for such materials have been explored; these include the use of off-stoichiometric thiol-ene networks and dendritic polymer scaffolds. In the first case, the highly efficient UV-induced thiol-ene coupling (TEC) reaction was used to create crosslinked polymeric networks with a predetermined and tunable excess of thiol or ene functionality. These materials rely on the use of readily available commercial monomers. By adopting standard molding techniques and simple TEC surface modifications, patterned surfaces with tunable hydrophobicity could be obtained. Moreover, these materials are shown to have great potential for rapid prototyping of microfluidic devices. In the second case, dendritic polymer scaffolds were evaluated for their ability to increase surface interactions and produce functional 3D networks. More specifically, a self-assembled dendritic monolayer approach was explored for producing highly functional dendronized surfaces with specific interactions towards pathogenic E. coli bacteria. Furthermore, a library of heterofunctional dendritic scaffolds, with a controllable and exact number of dual-purpose azide and ene functional groups, has been synthesized. These scaffolds were explored for the production of cell interactive hydrogels and primers for bone adhesive implants. Dendritic hydrogels decorated with a selection of bio-relevant moieties and with Young’s moduli in the same range as several body tissues could be produced by facile UV-induced TEC crosslinking. These gels showed low cytotoxic response and relatively rapid rates of degradation when cultured with normal human dermal fibroblast cells. When used as primers for bone adhesive patches, heterofunctional dendrimers with high azide-group content led to a significant increase in the adhesion between a UV-cured hydrophobic matrix and the wet bone surface (compared to patches without primers).

QC 20140116

Ongoing advances in tissue engineering with the goal to address the clinical shortage of donor organs have encouraged the design and development of biomaterials to be used in tissue-engineered scaffolds. Furthermore, biomaterials have been used as delivery vehicles for vaccines that aim to enhance the protective immunity against pathogenic agents. These tissue-engineered constructs or vaccines are usually combination products that combine biomaterial and biological (e.g. cells, proteins, and/or DNA) components. Upon introduction into the body, the host response towards these products will be a combination of both a non-specific inflammatory response towards the biomaterial and an antigen-specific immune response towards the biological component(s). Recently, the biomaterial component was shown to influence the immune response towards a co-delivered antigen. Specifically, poly(lactic-co-glycolic acid) (PLGA), but not agarose, scaffolds or microparticles (MPs) enhanced the humoral response to a model antigen, ovalbumin. This in vivo result echoed with the in vitro study that PLGA, but not agarose, supported a mature phenotype of dendritic cells (DCs), the most potent antigen-presenting cells. Therefore, it is hypothesized that the effect of biomaterials on DC phenotype may influence the adaptive immunity against a co-delivered antigen. Understanding how biomaterials affect DC response will facilitate the selection and design of biomaterials that direct a desired immune response for tissue engineering or vaccine delivery applications. The objectives of this research were to elucidate the correlations between material properties and DC phenotype, develop predictive models for DC response based on material properties, and uncover the molecular basis for DC response to biomaterials. Well-defined biomaterial systems, including clinical titanium (Ti) substrates and two polymer libraries, were chosen to study induced DC phenotype. Due to the time-consuming nature of conventional methods for assessing DC phenotype, a high-throughput (HTP) method was first developed to screen for DC maturation based on surface marker expression (CHAPTER 4). A 96-well filter plate-based HTP methodology was developed and validated for the assessment of DC response to biomaterials. A "maturation factor", defined as CD86/DC-SIGN and measured by immunostaining, was found to be a cell number-independent metric for DC maturation and could be adapted to screen for DC maturation in a microplate format. This methodology was shown to reproducibly yield similar results of DC maturation in response to biomaterial treatment as compared to the conventional flow cytometric method upon DC treatment in 6-well plates. In addition, the supernatants from each treatment could easily be collected for cytotoxicity assessment using glucose-6-phosphate dehydrogenase (G6PD)-based assay and cytokine profiling using multiplex technology. In other words, the 96-well filter plate-based methodology can generate three outcomes from one single cell culture: 1) maturation marker expression, 2) cytotoxicity, and 3) cytokine profile. To examine which material properties were critical in determining DC phenotype, a set of three clinical titanium (Ti) substrates with well-defined surfaces was used to treat DCs (CHAPTER 5). These Ti substrates included pretreatment (PT), sand-blasted and acid-etched (SLA), and modified SLA (modSLA), with different roughness and surface energy. DCs responded differentially to these substrates. Specifically, PT and SLA induced a mature DC (mDC) phenotype, while modSLA-treated DCs remained immature based on surface marker expression, cytokine production profiles and cell morphology. Both PT and SLA induced higher CD86 expression as compared to iDC control, while modSLA maintained CD86 expression at a level similar to iDC. PT- or SLA-treated DCs exhibited dendritic processes associated with a mDC phenotype, while modSLA-treated DCs were rounded, a morphology associated with an iDC phenotype. Furthermore, PT induced increased secretion of MCP-1 by DCs compared to iDCs, indicating that PT promoted a pro-inflammatory environment. SLA induced higher IL-16 production, which is a pleiotropic cytokine, by DCs, most likely as a pro-inflammatory response due to the enhanced maturation of DCs induced by SLA. In contrast, modSLA did not induced enhanced production of any cytokines examined. Principal component analysis (PCA) were used to reduce the multi-dimensional data space and confirmed these experimental results, and it also indicated that the non-stimulating property of modSLA co-varied with certain surface properties, such as high surface hydrophilicity, % oxygen and % titanium of the substrates. In contrast, high surface % carbon and % nitrogen were more associated with a mDC phenotype. Furthermore, PCA also suggested that surface line roughness (Ra) did not contribute to the expression of CD86, an important maturation marker, suggesting that roughness had little impact on DC response (CHAPTER 5). DC response-material property relationships were also derived using more complex materials from a combinatorial library of polymethacrylates (pMAs) (CHAPTER 6). Twelve pMAs were selected and were found to induce differential DC response using the HTP method described in CHAPTER 4. These pMAs resulted in a trend of increasing DC maturation represented by the metric CD86/DC-SIGN, which was consistent with the trends of the production of pro-inflammatory cytokine, TNF-α, and chemokine, IL-8. Interestingly, this set of pMAs induced an opposite trend of IL-16 production, which is most likely released as an anti-inflammatory cytokine in this situation. These polymers were characterized extensively for a number of material properties, including surface chemical composition, glass transition temperature (Tg), air-water contact angle, line roughness (Ra), surface roughness (Sa), and surface area. Similar to the results from the Ti study, PCA determined that surface carbon correlated with enhanced DC maturation, while surface oxygen was associated with an iDC phenotype. In addition, Tg, Ra, and surface area were unimportant in determining DC response. Partial square linear regression (PLSR), a multivariate modeling approach, was implemented using the pMAs as the training set and a separate polymer library, which contained methacrylate- and acrylate-based terpolymers, as the prediction set. This model successfully predicted DC phenotype in terms of surface marker expression with R2prediction = 0.76. Furthermore, prediction of DC phenotype was effective based on only theoretical chemical composition of the bulk polymers with R2prediction = 0.80 (CHAPTER 6). Nonetheless, one should note that a predictive model can be only as good as what it is trained on and cannot be used to predict the DC response induced by a type of materials different from the training set. Also, this model might not contain all the important material properties such as polymer swelling and cannot predict specific types of immune responses. However, these results demonstrated that a generalized immune cell response can be predicted from biomaterial properties, and computational models will expedite future biomaterial design and selection (CHAPTER 6). From the pMA library, pMAs that induced the two extremes of DC phenotype (mature or immature) were identified for elucidating the mechanistic basis of biomaterial-induced DC responses (CHAPTER 7). Two pMAs, polyhydroxyethylmethacrylate (pHEMA) and poly(isobutyl-co-benzyl-co-terahydrofurfuryl)methacrylate (pIBTMA), were selected because they induced the least and the most mature DC phenotype, respectively. These pMAs were used to elucidate the activation profiles of transcription factors in DCs after biomaterial treatment and were compared to the iDC and mDC controls. In addition, a combined treatment of pHEMA and LPS was also included to determine if pHEMA could maintain an iDC phenotype in the presence of LPS. Interestingly, pIBTMA induced DC maturation primarily through the activation of NF-κB, while pHEMA mediated suppression of DC maturation through multiple TFs, including the activation of ISRE, E2F-1, GR-PR, NFAT, and HSF. GR-PR and E2F-1 have been shown to be associated with the suppression of DC maturation; ISRE, E2F-1, and NFAT are linked to apoptosis induction; HSF regulates the production of heat shock proteins (HSPs) that induce DC maturation and inhibit apoptosis. The activation of HSF by pHEMA was most likely a natural defensive mechanism against the other apoptotic signals. Therefore, pHEMA suppressed DC maturation through the induction of apoptosis. Surprisingly, in the presence of pHEMA, the effect of LPS was completely eliminated, suggesting that biomaterials can override the effect of soluble factors. The morphology and surface marker expression of DCs treated with these different biomaterials or controls were consistent with TF activation profiles (CHAPTER 7). Overall, this research illustrates that biomaterial properties, within the chosen biomaterial space, can be correlated to DC phenotype and more importantly, can be used as predictors for relative levels of DC phenotype. Furthermore, the differential responses induced by different biomaterials were mediated through the distinct activation profiles of transcription factors. Together, these findings are expected to facilitate the design and selection of biomaterials that direct desired immune responses.

Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2006.
Babensee, Julia, Committee Chair ; Andres Garcia, Committee Member ; Mary Marovich, Committee Member ; Barbara Boyan, Committee Member ; Elliot Chaikof, Committee Member ; Cheng Zhu, Committee Member.

The use of metals like titanium (Ti) and vanadium (V) are common in many medical implants for orthopaedic and orthodontic purposes. The most frequent cause of implant failure is aseptic loosening, resulting from an inflammatory reaction and increased osteolysis at the bone-metal interface. Currently, the pathophysiological mechanism of aseptic loosening remains poorly understood. One hypothesis suggests the reactivity of immune cells (metal hypersensitivity) towards metal ions released through the biocorrosion of metal implants. This thesis examines the effects of titanium and vanadium ions on various immune cells like monocytes, dendritic cells (DCs) and T-lymphocytes. Thereby investigating the role and mechanism which titanium and vanadium plays in aseptic loosening. Through energy filtered transmission electron microscopy, the accumulation of titanium ions was visualized in human monocyte-derived DCs and T-lymphocytes after 24 hours exposure. Titanium was seen to co-localise with phosphorous-rich regions, like the cell membrane, organelles and nucleus of these cells. Flow cytometry measured changes in the cell surface marker expression of monocytes, osteoclasts, DCs and T-lymphocytes treated with the metals. Monocytes exposed to titanium (IV) showed an increase of Tartate-Resistant Acid Phosphatase (TRAP), important for osteolysis and indicative of differentiation towards an osteoclast-like phenotype. DCs treated with Ti(IV) and vanadium (III) had reduced antigen presenting MHC class II expression, but not a reduced capacity to proliferate non-adherent peripheral blood monocytic cells (naPBMCs). Under the influence of Ti(IV), T-lymphocytes, DCs and monocytes expressed elevated levels of the chemokine receptor, CCR4. This would allow for the migration of CCR4+ cells towards the bone and skin regions. Functional changes were measured with BrdU incorporation proliferation assays, cytokine assays (CBA Kits) and the successful generation of titanium-specific T-lymphocytes from Ti(IV) treated DCs. Ti(IV) specific T-lymphocytes conceptually shows the possible formation of an antigenic titanium-protein complex, which can be recognized by the immune system. DCs treated with Ti(IV) and V(III) were able to cause the proliferation of naPBMCs, even with a reduced antigen presenting capability. However, there was no additional influence of V(III) on the immune response through DCs. Cytokines released by DCs and T-lymphocytes after Ti(IV) treatments showed a skew towards an inflammatory Th1-type response through the release of TGF-! and IL-12p70. Activated T-lymphocytes exposed to Ti(IV) also released RANK-L, which drives osteoclastogenesis and subsequently increased osteolysis. The research supports and suggests an interaction between immune and bone cells where titanium-induced inflammation drives an osteolytic cycle that prevents the integration of metal implants into the bone. Hence, suggesting a mechanism for implant failure through aseptic loosening in patients with titanium-vanadium implants.

Le travail présenté dans ce manuscrit décrit la conception et la synthèse d'architectures cœur-couronnes à base de polymères dendritiques, ainsi que les différents états d'assemblage de ces polymères (phases lyotropes, hydrogels, cristaux liquides) et enfin l'incorporation de nanoparticules d'or dans ces systèmes. Différents types de cœurs ont été utilisés dans ce projet: des polymères hyper-ramifiés polyamidoamine, des dendrimères de polyamidoamine et des dendrigrafts de polylysine. Ces cœurs ont été fonctionnalisés soit avec un polymère thermosensible de type poly(N-isopropylacrylamide) via un couplage amide, soit avec un tensio-actif comme le dodécyl sulfate de sodium ou avec des copolymères présentant des séquences ioniques, ces deux derniers cas via des interactions ioniques. Les polymères cœur-couronne s'organisent en phases organisées lyotropes ou thermotropes en fonction de leurs architectures et de leur environnement. Les différentes phases formées par ces structures ont été utilisées pour stabiliser des nanoparticules d'or préformées ou pour les synthétiser in situ. L'influence de la présence de nanoparticules sur l'organisation du polymère et sur les propriétés des systèmes hybrides (mécaniques, stabilisation. . . ) a été étudiée. En outre, l'influence de ces systèmes sur la croissance de nanoparticules formées in situ a été évaluée. La taille des nanoparticules d'or est dictée par la nature de la phase organisée qui est elle-même liée à la structure du polymère hyper-ramifié
The work presented in this manuscript describes the design and synthesis of core-shell architectures based on dendritic polymers, as well as the different assemblage states of those polymers (lyotropic phases, hydrogels, liquid crystals) and finally the incorporation of gold nanoparticles inside such systems. Different types of cores were used in this project: polyamidoamine hyperbranched polymers, polyamidoamine dendrimers and polylysine dendrigrafts. These cores were functionalized either with thermoresponsive poly(N-isopropylacrylamide) via an amide coupling, or with sodium dodecyl sulfate surfactant by ionic interactions, or with ionic block copolymers also by ionic interactions. The core-shell polymers organized into aggregates in aqueous solution, gels or liquid crystals depending on their architectures and their environment. All the phases formed by these structures were used to in situ synthesize gold nanoparticles as well as to stabilize preformed gold nanoparticles. The changes in these phases induced by the incorporation of nanoparticles as well as the properties of the hybrid systems (mechanical, liquid crystal character, stability. . . ) were presented. Furthermore, the " soft-template " effect of these systems on the size of the in situ formed nanoparticles was studied. The size of gold nanoparticles was governed by the nature of the assembled phase related to the structure of the hyperbranched polymer

The host response toward biomaterial component of tissue-engineered devices has been extensively investigated. The objective of this research was to understand the response of dendritic cells (DCs) to different biomaterials upon contact and identify biomaterials suitable for use in tissue engineering constructs for rheumatoid arthritis (RA) applications. Differential levels of functional DC maturation were observed depending on the type of biomaterial in 2-dimensional films or 3-dimensional scaffolds used to treat immature DCs; Poly(lactic-co-glycolic acid) (PLGA) or chitosan supported higher levels of DC maturation, as compared to immature DCs. Alginate supported moderate levels of DC maturation. Agarose did not support DC maturation whereas hyaluronic acid inhibited DC maturation. Further, these DCs treated with different biomaterials induced differential phenotype and polarization of autologous T cells upon co-culture of DCs and T cells; DCs treated with PLGA induced T helper type I with immunogenic response while DCs treated with agarose did T helper type II with tolerogenic response. Effect of different biomaterials (PLGA and agarose) was assessed in vivo upon implantation of them into the knee joint of RA-induced rabbit. Total leukocyte concentrations in the peripheral blood or in the joint lavage of the left knees (untreated control) were observed in differential levels depending on the biomaterial implant, possibly due to the systemic circulation of the peripheral blood. Furthermore, cartilage and bone healing progression was differentially observed in the osteochondral defect of the knee joint of RA-induced rabbit, depending on type of biomaterial scaffold implanted into the defect. Collectively, these results demonstrate the multifunctional impacts of inherently different biomaterials on in vitro immunomodulation of phenotype and polarization of DCs and autologous T cells. Furthermore, taken together with these immunomodulatory impacts of biomaterials, in vivo effects of different biomaterial scaffolds on RA environment shown in this study can suggest the criteria of selection and design of biomaterials for orthopedic tissue engineering, which may ultimately be best integrated into the diseased cartilage and bone.

Automotive industry products portfolio includes a wide variety of complex‐shaped cast iron products, such as truck engine components, that need to withstand a constant trend of higher demands, especially urged by stricter environmental regulations on emissions. Combined with this continued demand on properties improvement, cast iron industry faces a process problem related to the lack of understanding of solidification and mechanisms behind defect formation. Casting products are highly affected by the product design and the manufacturing method itself, which governs the final microstructure and hence the final mechanical properties. Wall thickness of the moulding material strongly influences the solidification time, varying the microstructural coarseness, resulting in a component with different properties depending on the local shape of the casting. The main objective of this work is the characterization of the primary austenite microstructure and its coarsening process, which has been poorly documented in cast iron literature, to allow the prediction and control of these microstructural features present in the casting. The microstructural evolution of the primary austenite in hypoeutectic lamellar graphite iron (LGI) is studied under isothermal coarsening conditions. The dendritic microstructure suffered major morphological changes that included dendrite fragmentation, globularization, and coalescence. Empirical relations based on morphological parameters are introduced to predict the microstructural evolution of primary austenite. A novel technique for colour‐etching and semi‐automatic image analysis for the characterization of quenched dendritic microstructures in cast iron is presented. A new experimental technique for production of graphitic iron with varying nodularity is presented as a solution to control the production of compacted (CGI) and spheroidal graphite iron (SGI) under laboratory conditions. The nodularity evolution is controlled as a function of the holding time and the residual Mg, allowing the study of the primary solidification and primary microstructures of hypoeutectic CGI and SGI in future investigations.

This thesis deals with the engineering of novel nanomaterials, particularly nanocomposites and nanostructured surfaces with enhanced functionalities. The study includes two parts; in the first part, an in situ sol-gel polymerization approach is used for the synthesis of polymer-inorganic hybrid material and its exceptional transparent UV-shielding effect has been investigated. In the second part, electrodeposition process has been adapted to engineer surfaces and the boiling performance of the fabricated nanostructured surfaces is evaluated.

In the first part of the work, polymer-inorganic hybrid materials composed of poly(methylmethacrylate) (PMMA) and zinc compounds were prepared by in situ sol-gel transition polymerization of zinc complex in PMMA matrix. The immiscibility of heterophase of solid organic and inorganic constituents was significantly resolved by an in situ sol-gel transition polymerization of ZnO nanofillers within PMMA in the presence of dual functional agent, monoethanolamine, which provided strong secondary interfacial interactions for both complexing and crosslinking of constituents.

In the second part of the work, nanoengineering on the surface of copper plates has been performed in order to enhance the boiling heat transfer coefficient. Micro-porous surfaces with dendritic network of copper nanoparticles have been obtained by electrodeposition with dynamic templates. To further alter the grain size of the dendritic branches, the nanostructured surfaces underwent a high temperature annealing treatment.

Comprehensive characterization methods of the polymer-inorganic hybrid materials and nanoengineered surfaces have been undertaken. XRD, 1H NMR, FT-IR, TGA, DSC, UV-Vis, ED, SEM, TEM and HRTEM have been used for basic physical properties. Pool boiling tests were performed to evaluate the boiling performance of the electrodeposited nanostructured micro-porous structures.

The homogeneous PZHM exhibited enhanced UV-shielding effects in the entire UV range even at very low ZnO content of 0.02 wt%. Moreover, the relationship between band gap and particle size of incorporated ZnO by sol-gel process was in good agreement with the results calculated from the effective mass model between bandgap and particle size. The fabricated enhanced surface has shown an excellent performance in nucleate boiling. At heat flux of 1 W/cm2, the heat transfer coefficient is enhanced over 15 times compared to a plain reference surface. A model has been presented to explain the enhancement based on the structure characteristics.

The ammonium chloride-water system has been used extensively as a transparent metal analog to model solidification in binary metal alloys. In this work, the growth rate and morphology of NH₄Cl dendrites grown from aqueous solutions were studied. Since an accurate knowledge of the materials parameters is essential to predicting the growth behavior, the equilibrium segregation coefficient was measured and a detailed analysis of the other NH₄Cl-H₂O materials properties cited in the literature was conducted. Isothermal experiments on bulk NH₄Cl-H₂O samples confirmed that the previously reported discontinuity in the growth rate as function of undercooling and associated transition from <100> oriented slowly growing dendrites to rapidly growing <111> dendrites are not artifacts of the sample geometry. Directional solidification experiments conducted to study the dendrite growth morphology revealed oscillations in both the growth rate and orientation. Results from these studies show that both the undercooling at which the <100> to <111> transition occurs and the peak velocity vary with composition. However, the observed shifts toward smaller apparent undercoolings and the narrowing of the oscillations at higher drive velocities result from changes in the local composition caused by the velocity and orientation dependencies of the partition coefficient. The oscillatory behavior of the <111> dendrites can be predicted using the residual <100> compositional field and the applied temperature gradient. By using an anisotropic segregation coefficient, the slow and fast growth rates can be separately modeled as a function of undercooling using the standard dendrite growth equations. While the transition to the <111> morphology can be attributed to the anisotropy in the k-value, several modifications need to be made to the existing dendritic growth models in order to describe the critical transition. Due to the complex relationships between the non-equilibrium segregation coefficient, composition, and growth rate, some of these modeling efforts have been left to future researchers. In addition to the inclusion of the overall anisotropy, our experiments indicate that the long-range compositional and thermal field effects must be incorporated into the dendrite growth models to explain the difference in growth rates of <111> Primary branches when <111> or <100> side-branches are present.

The next generation of rechargeable batteries must have significantly improved gravimetric and volumetric energy densities while maintaining a long cycle life and a low risk of catastrophic failure. Replacing the conventional graphite anode in a lithium ion battery with lithium foil increases the theoretical energy density of the battery by more than 40%. Furthermore, there is significant interest within the scientific community on new cathode chemistries, like sulfur and air, that presume the use of a lithium metal anode to achieve theoretical energy densities as high as 5217 W˙h/kg. However, lithium metal is highly unstable toward traditional liquid electrolytes like ethylene carbonate and dimethyl carbonate. The solid electrolyte interphase that forms between lithium metal and these liquid electrolytes is brittle which causes a highly irregular current distribution at the anode, resulting in the formation of lithium metal protrusions. Ionic current concentrates at these protrusions leading to the formation of lithium dendrites that propagate through the electrolyte as the battery is charged, causing it to fail by short-circuit. The rapid release of energy during this short-circuit event can result in catastrophic cell failure.

Polymer electrolytes are promising alternatives to traditional liquid electrolytes because they form a stable, elastomeric interface with lithium metal. Additionally, polymer electrolytes are significantly less flammable than their liquid electrolyte counterparts. The prototypical polymer electrolyte is poly(ethylene oxide). Unfortunately, when lithium anodes are used with a poly(ethylene oxide) electrolyte, lithium dendrites still form and cause premature battery failure. Theoretically, an electrolyte with a shear modulus twice that of lithium metal could eliminate the formation of lithium dendrites entirely. While a shear modulus of this magnitude is difficult to achieve with polymer electrolytes, we can greatly enhance the modulus of our electrolytes by covalently bonding the rubbery poly(ethylene oxide) to a glassy polystyrene chain. The block copolymer phase separates into a lamellar morphology yielding co-continuous nanoscale domains of poly(ethylene oxide), for ionic conduction, and polystyrene, for mechanical rigidity. On the macroscale, the electrolyte membrane is a tough free-standing film, while on the nanoscale, ions are transported through the liquid-like poly(ethylene oxide) domains.

Little is known about the formation of lithium dendrites from stiff polymer electrolyte membranes given the experimental challenges associated with imaging lithium metal. The objective of this dissertation is to strengthen our understanding of the influence of the electrolyte modulus on the formation and growth of lithium dendrites from lithium metal anodes. This understanding will help us design electrolytes that have the potential to more fully suppress the formation of dendrites yielding high energy density batteries that operate safely and have a long cycle life.

Synchrotron hard X-ray microtomography was used to non-destructively image the interior of lithium-polymer-lithium symmetric cells cycled to various stages of life. These experiments showed that in the early stages of lithium dendrite development, the bulk of the dendritic structure was inside of the lithium electrode. Furthermore, impurity particles were found at the base of the lithium dendrites. The portion of the lithium dendrite protruding into the electrolyte increased as the cell approached the end of life. This imaging technique allowed for the first glimpse at the portion of lithium dendrites that resides inside of the lithium electrode.

After finding a robust technique to study the formation and growth of lithium dendrites, a series of experiments were performed to elucidate the influence of the electrolyte’s modulus on the formation of lithium dendrites. Typically, electrochemical cells using a polystyrene – block¬ – poly(ethylene oxide) copolymer electrolyte are operated at 90 °C which is above the melting point of poly(ethylene oxide) and below the glass transition temperature of polystyrene. In these experiments, the formation of dendrites in cells operated at temperatures ranging from 90 °C to 120 °C were compared. The glass transition temperature of polystyrene (107 °C) is included in this range resulting in a large change in electrolyte modulus over a relatively small temperature window. The X-ray microtomography experiments showed that as the polymer electrolyte shifted from a glassy state to a rubbery state, the portion of the lithium dendrite buried inside of the lithium metal electrode decreased. These images coupled with electrochemical characterization and rheological measurements shed light on the factors that influence dendrite growth through electrolytes with viscoelastic mechanical properties. (Abstract shortened by ProQuest.)

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Pistons are one of the most challenged components on an internal combustion engine. The range of thermal and mechanical loads on these components reach limit levels where the applied materials cannot react and are not able to go back to its original condition. We can say that pistons are the fuses of an internal combustion engine. The adequate selection of materials for the pistons must take in account the usage of the engines. For passenger cars for instance, typically light alloys are chosen in order to attend the low fuel consumption and emission level demands. For commercial vehicles there are more freedom choosing the materials because weight does not play the same level of role but on the other hand requires materials that can resist the very high loads involved. The objective of this work is to describe the criteria s involved on a piston design and how closed they are connected with the adequate material selection. A case study of a aluminum piston for Diesel engine application that presented a pin bore crack related to feathery grain formation will be shown.
Os pistões são um dos componentes mais solicitados em um motor de combustão interna. O conjunto de cargas térmicas e mecânicas nestes componentes chega a atingir limites onde os materiais empregados não conseguem mais reagir de maneira a retornar a sua condição original. Pode-se dizer que os pistões são os fusíveis de um motor à combustão interna. A escolha dos materiais mais adequados para a confecção dos pistões passa por um critério de seleção que deve levar em conta o tipo de aplicação dos motores. A aplicação de motores em carros de passeio por exemplo, tipicamente exige a utilização de ligas mais leves em seus componentes visando atender aos requisitos de redução do consumo de combustíveis e também de emissão de poluentes. Já para a aplicação em veículos utilitários pesados existe uma maior liberdade para a escolha dos materiais dos componentes pois o peso já não tem a mesma influência sobre a performance mas por outro lado exige a utilização de materiais mais resistentes devido às altas cargas envolvidas. O objetivo do trabalho é discorrer também sobre os critérios envolvidos no projeto dos pistões e como eles estão correlacionados com a escolha dos materiais mais adequados. Será mostrado também um estudo de caso de um pistão de alumínio aplicado em um motor Diesel e que apresentou uma trinca no cubo relacionada à formação de dendritas gêmeas.

This thesis ventures with the extracellular matrix protein (ECM) fibronectin (FN) as an interface protein in the interaction between cells and materials to design microenvironment for future use in tissue engineering. It is studied the FN adsorption and conformations, cell behaviour to different FN conformation, cell adhesion, reorganisation and remodelling of FN at the material interface, the role of growth factors (GF) and their interactions with components of the extracellular matrix (ECM), the immunology cell response, and the stem cell fate influenced by the extrinsic signals coming from the engineered microenvironments using ECM's proteins. To investigate the FN response, in terms of adsorbed amount and conformation to different chemical properties of the material, model surfaces were used. Self assembled monolayers (SAM) with different percentages of two different chemical groups were used: CH3 and OH. FN adsorption, initial cell adhesion and signalling (focal adhesions, integrin expression and phosphorylation of FAK) is related with the reorganisation and secretion of FN and matrix degradation. It is shown that matrix degradation at the cell material interface depends on surface chemistry in metalloproteinase-dependent way. A direct relationship between FN activity at the cell-material interface and metalloproteinase 9 (MMP9) expression was found, being the product of a sequence of events that include integrin expression, focal adhesion formation, matrix reorganisation and focal adhesion kinase (FAK) phosphorylation. Two different materials with subtle variations in their chemical composition were employed as a drastically different FN conformation: from a globular conformation on PMA (poly (methyl acrylate)) to the formation of a well-interconnected FN network (similar to the FN physiological fibrillar network) triggered by PEA (poly (ethyl acrylate)). The formation of focal adhesions (vinculin), FAK expression and phosphorylation, specific integrin binding, protein and gene expression for ¿5 and ¿v was studied, seeking to correlate cell adhesion with matrix degradation. It is demonstrated that the material-driven FN fibrillogenesis on PEA triggers proteolytic activity: MMP activity is higher as a compensatory mechanism to the inability of cells to reorganise this FN network. Looking into the role of protein-material interactions and stem cell fate, and with the knowledge on PEA, we engineer different synergistic microenvironments to direct cell and stem cell fate. FN has a growth factor (GF) binding domain on its molecule (FNIII12-14) and has been demonstrated to produce a synergistic response when occurs at the same time the recognition of the cell binding domain (FNIII9-10). It is demonstrated that this domain is available on the FN coated PEA, and exploiting these interactions between PEA, FN and GF, it is developed a microenvironment to control cell behaviour and tissue repair. It is studied the BMP2 binding and presentation, the effect of BMP2 presentation on MSC proliferation and differentiation. These systems allow not only enhanced activity of GF compared to soluble administration, but also reduce GF doses, improving safety and cost effectiveness. Finally, the immunological reaction of the microenvironment developed is studied using dendritic cells, beside the conformational structure of ECM protein importance in DC integrin-based activation it is studied, helping to establish the field of adhesion-based modulation of DC as a general mechanism that has previously not been defined. The microenvironment didn't induce any maturation in DC, while different FN conformation shows differences in DC morphology and citokine level production (IL-10 and IL-12).
En esta tesis se estudia la interacción de una proteina de la matriz extracelular, fibronectina (FN) como interfase en la interacción entre células y materiales, para diseñar microambientes con el propósito de ser usados en el futuro en ingeniería tisular. Se estudia la adsorción y conformación de FN y la relación con el diferente comportamiento celular: la adhesión celular, la reorganización y remodelado de la FN en la interfase célula-material, el papel que juegan los factores de crecimiento y sus interacciones con los componentes de la matriz extracelular, la respuesta immunológica y el destino celular de células madre influenciadas por las señales extrínsecas provenientes de microambientes elaborados a partir de proteínas de la matriz extracelular. Con el objetivo de investigar la respuesta a la FN en términos de conformación y cantidad absorbida a diferentes propiedades químicas del material, se usaron materiales modelo: monocapas autoensambladas (self-assembled monolayers, SAM). Las químicas estudiadas fueron CH3 and OH. La adsorption de FN, adhesion y señalización (adhesiones focales, expresión de interinas y fosforilación de quinasas de adhesiones focales (FAK)) se estudiaron en relación a la reorganización y secreción de FN y degradación de la matriz extracelular. Se demuestra que la degradación de la matriz extracelular en la interfase célula-material depende de la química de la superficie, a través de las metaloproteinasas. Se ha descubierto una relación directa entre la actividad de la FN que se encuentra en el material y la expresión de metaloproteinasa 9 (MMP9), a través de la expresión de integrinas, formación de adhesiones focales, reorganización de la matriz extracelular y fosforilación de FAK En el siguiente capítulo se emplean materiales poliméricos con una sutil diferencia en la composición química, provocando una diferencia drástica en la conformación de la FN: se pasa de una conformación globular en PMA (polimetil acrilato) a una conformación en forma de red interconectada en PEA (polietil acrilato). Con el propósito de relacionar la adhesión celular con la degradación de la matriz extracelular, se estudia la formación de adhesiones focales (vinculina), la expresión y fosforilación de FAK, la unión específica de integrinas y la expresión de las integrinas ¿5 and ¿v. Se demuestra que la formación de una red de FN sobre PEA induce la actividad proteolítica: la actividad de las MMPs es mayor, actuando como mecanismo compensatorio a la incapacidad de reorganización de la red de FN. Haciendo uso de la conformación de la FN sobre PEA, se estudiaron las interacciones entre la proteína-material y el destino celular de células madres. La FN posee un dominio de unión de factores de crecimiento (FNIII12-14) y se ha demostrado que se produce una respuesta sinérgica cuando el reconocimiento ocurre junto con el dominio de unión celular (FNIII9-10). En esta tesis se demuestra que el dominio de unión de factores de crecimiento está disponible en la conformación que adquiere sobre PEA y se diseñan microambientes para controlar el comportamiento celular y regeneración de tejido. Se estudia la unión y presentación de BMP2 y su efecto en la diferenciación de células madre mesenquimales. Los microambientes desarrollados, ademas de mejorar la actividad de los factores de crecimiento comparado con la administración soluble, también reduce la cantidad de factores de crecimiento que se tendría que administrar, mejorando la seguridad y efectividad. Finalmente se estudió la reacción inmunológica a los microambientes desarrollados usando células dendríticas, estudiando además la influencia de la estructura de la conformación de las proteínas en la activación de las células dendríticas a través de las integrinas. Los microambientes no indujeron ninguna maduración de células dendríticas, mientras que la conformación de la FN muestra control
En aquesta tesi s'estudia la interacció entre una proteïna de la matriu extracel.lular, fibronectina (FN) com interfase en la interaccio entre cèl·lules i materials, per a dissenyar microambients amb el propòsit d'utilitzar-se al futur en enginyeria tissular. S'estudia l'adsorció i conformació de la FN i la relació amb el diferent comportament cel·lular: l'adhesió cel·lular, la reorganització i remodelat de la FN a la interfase cèl·lula-material, el paper que juguen els factors de creixement i les seus interaccions amb els components de la matriu extracel·lular, la resposta immunològica i el destí cel·lular de cèl·lules mare influenciades pels senyals extrínseques provinents de microambients elaborats a partir de proteïnes de la matriu extracel·lular. Amb l'objectiu d'investigar la respostar a la FN en termes de conformació i quantitat absorbida a diferents propietats químiques del material, s'utilitzaren materials model: monocapes autoacoblades (self-assembled monolayers, SAM). Les químiques estudiades van ser CH3 and OH. L'absorció de FN, adhesió i senyalització (adhesions focals, expressió d'integrines i fosforilació de quinases d'adhesions focals (FAK)) es van estudiar en relació a al reorganització i secreció de la FN i degradació de la matriu extracel·lular. Es demostra que la degradació de la matriu extracelular en la interfase cèl·lula-material depèn de la química de la superficie, a través de les metal·loproteïnases. S'ha descobert una relació directa entra l'activitat de la FN que es troba en el material i l'expressió de metaloproteinasa 9, a través de l'expressió d'integrines, formació d'adhesions focals, reorganització de la matriu extracel·lular i fosforilació de FAK. Al següent capítol es fan servir materials polimèrics amb una subtil diferència en la composició química, provocant una diferència dràstica en la conformació de la FN: es passa d'una conformació globular en PMA (polimetil acrilat) a una conformació en forma de xarxa interconnectada en PEA (polietil acrilat). Amb el propòsit de relacionar l'adhesió cel·lular amb la degradació de la matriu extracel·lular, s'estudia la formació d'adhesions focals (vinculina), l'expressió i fosforilació de FAK, la unió específica d'integrines i l'expressió de les integrines ¿5 and ¿v. Es demostra que la formació d'una xarxa de FN sobre PEA indueix l'activitat proteolítica: l'activitat de les MMPs és més gran, actuant com a mecanisme compensatori a la incapacitat de reorganització de la xarxa de FN. Fent ús de la conformació de la FN sobre PEA, es van estudiar les interaccions entre la proteïna-material i el destí cel·lular de cèl·lules mares. La FN posseeix un domini d'unió de factors de creixement (FNIII12-14) i s'ha demostrat que es produeix una resposta sinèrgica quan el reconeixement ocurreix juntament amb el domini d'unió cel·lular (FNIII9- 10). En aquesta tesi es demostra que el domini d'unió de factors de creixement està disponible a la conformació que adquireix sobre PEA i es dissenyen microambients per controlar el comportament cel·lular i regeneració de teixit. S'estudia la unió i presentació de BMP2 i el seu efecte en la diferenciació de cèl·lules mare mesenquimals. Els microambientes desenvolupats, a més de millorar l'activitat dels factors de creixement comparat amb l'administració soluble, també redueix la quantitat de factors de creixement que s'hauria d'administrar, millorant la seguretat i efectivitat. Finalment es va estudiar la reacció immunològica als microambients desenvolupats usant cèl·lules dendrítiques, estudiant a més la influència de l'estructura de la conformació de les proteïnes en l'activació de les cèl·lules dendrítiques a través de les integrines. Els microambients no van induir cap maduració de cèl·lules dendrítiques, mentre que la conformació de la FN mostra controlar la morfologia de les cèl·lules dendrítiques i
Llopis Hernández, V. (2017). Material-driven fibronectin fibrillogenesis to engineer cell function [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90412
TESIS

A demanda por aumento da eficiência energética vem obrigando empresas e centros de pesquisa a desenvolver e utilizar novos materiais buscando a redução de peso. Entre esses materiais, destacam-se as ligas de magnésio, com aproximadamente dois terços da densidade do alumínio e a melhor relação peso/resistência entre os metais. Porém, a utilização do magnésio em altas temperaturas tem suas limitações, devido à baixa resistência a fluência e a formação do precipitado -Mg17Al12 que tem baixo ponto de fusão, tornando as ligas de magnésio mais suscetíveis aos efeitos de deslizamento nos contornos de grãos. Algumas ligas de magnésio contendo elementos terras raras foram desenvolvidas para melhorar a resistência a fluência. O trabalho em questão visa analisar o comportamento da liga Mg6Al3La1Ca, correlacionando os parâmetros de solidificação com as propriedades mecânicas: dureza, alongamento específico, limite de escoamento e limite de resistência à tração. Para isso, foram solidificados unidirecionalmente, com atmosfera de argônio, três lingotes da liga Mg6Al3La1Ca a partir de sobreaquecimento de 780°C, 715°C e 650°C. O resfriamento dos lingotes ocorreu no forno e por resfriamento forçado. Os resultados obtidos de limite de resistência à tração, limite de escoamento e dureza tem uma relação direta com a temperatura de vazamento onde os melhores resultados foram obtidos com as temperaturas mais elevadas. Portanto, conclui-se que na temperatura de 780°C com resfriamento forçado foram obtidas as melhores propriedades mecânicas.
The demand for increased energy efficiency is forcing companies and research centers to develop and use new materials aimed at reducing weight. Among these materials, there is magnesium alloys, because it has about two-thirds of the density of aluminum and the best weight/resistance between the metals. However, the use of magnesium at elevated temperatures has its limitations due to low resistance to creep; the formation of -Mg17Al12 precipitate which has a low melting point makes the magnesium alloy more susceptible to slip around the grains. Some magnesium alloys containing rare earth elements have been developed to improve resistance to creep. The work in question is to analyze the behavior the Mg6Al3La1Ca alloy, correlating the parameters of solidification with the mechanical properties: hardness, specific elongation, limits yield strength and tensile strength. For that, three ingots of the alloy Mg6Al3La1Ca were solidified unidirectionally using argon atmosphere with overheating of 780°C, 715°C and 650°C. The cooling of ingots occurred in the furnace and by forced cooling. The results of limit tensile strength, yield strength and hardness have a direct relation with the pouring temperature where the best results were obtained with higher temperatures. Therefore, it is concluded that the best mechanical properties were obtained at temperature of 780°C with forced cooling.

This thesis entails a detailed microstructure analysis of directionally solidified (DS) Al-7Si alloys processed in microgravity aboard the International Space Station and similar duplicate ground based experiments at Cleveland State University. In recent years, the European Space Agency (ESA) has conducted experiments on alloy solidification in microgravity. NASA and ESA have collaborated for three DS experiments with Al- 7 wt. % Si alloy, aboard the International Space Station (ISS) denoted as MICAST6, MICAST7 and MICAST12. The first two experiments were processed on the ISS in 2009 and 2010. MICAST12 was processed aboard the ISS in the spring of 2014; the resulting experimental results of MICAST12 are not discussed in this thesis. The primary goal of the thesis was to understand the effect of convection in primary dendrite arm spacings (PDAS) and radial macrosegregation within DS aluminum alloys. The MICAST experiments were processed with various solidification speeds and thermal gradients to produce alloy with differences in microstructure features. PDAS and radial macrosegregation were measured in the solidified ingot that developed during the transition from one solidification speed to another. To represent PDAS in DS alloy in the presence of no convection, the Hunt-Lu model was used to represent diffusion-controlled growth. By sectioning cross-sections throughout the entire length of solidified samples, PDAS was measured and calculated. The ground-based (1-g) experiments done at Cleveland State University CSU were also analyzed for comparison to the ISS experiments (0-g). During steady state in the microgravity environment, there was a reasonable agreement between the measured and calculated PDAS. In ground-based experiments, transverse sections exhibited obvious radial macrosegregation caused by thermosolutal convection resulting in a non-agreement with the Hunt- Lu model. Using a combination of image processing techniques and Electron Microprobe Analysis, the extent of radial macrosegregation was found to be a function of processing conditions and PDAS.

Les batteries à électrode lithium métal ont des capacités théoriques élevées, une différence de potentiel importante, des géométries adaptables. Leur développement à l'échelle industrielle est pourtant compromis par l'électrodépôt d'agrégats irréguliers de lithium (dendrites) lors de la recharge de la batterie. La croissance dendritique à faible densité de courant est mal comprise, et semble liée à une mauvaise distribution de la densité de courant locale du fait des inhomogénéités à l'interface lithium/électrolyte. Ce manuscrit présente nos résultats sur des cellules symétriques Li/Electrolyte/Li qui permettent d'étudier simultanément le dépôt et la dissolution du lithium. Ces cellules sont basées sur des systèmes à base de POE+LiTFSI fonctionnant à 80°C, et sur des systèmes à base de PVdF-HFP/POE imbibé en EC:PC+LiTFSI et fonctionnant à température ambiante. Nous avons étudié ces cellules par visualisation in situ de l'espace inter-électrodes, et par spectroscopie d'impédance. Sur des cellules de visualisation à base d'électrolyte polymère fondu chargé en sel coloré, nous avons observé l'évolution des profils d'absorption optique directement liés aux profils de concentration dans l'électrolyte. Sur le système à base d'électrolyte gélifié nous avons constaté des variations locales de densité de courant en cours de polarisation. Par impédance, nous mettons en évidence la présence de deux couches de passivation à l'interface lithium/électrolyte qui évoluent différemment en vieillissement. Lorsqu'on polarise une cellule à courant constant, sa réponse en tension met en évidence la présence d'un milieu peu diffusif à l'interface entre le lithium et l'électrolyte.

Orientador: Amauri Garcia
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A procura por relações funcionais correlacionando parâmetros microestruturais e o comportamento mecânico de ligas metálicas é fundamental para a pré-programação do produto final. O presente estudo pretende contribuir para o entendimento sobre a influência dos parâmetros microestruturais na resistência ao desgaste e nas propriedades mecânicas de ligas de dois sistemas binários: AI-Sn e AI-Si. Tais ligas são bastante usadas em aplicações de engenharia, tais como mancais e camisas de cilindro de motores de combustão, respectivamente. Apesar do grande uso das ligas do sistema AI-Sn como material tribológico, são escassos os estudos sobre o desenvolvimento microestrutural destas ligas na literatura. Neste estudo, quatro ligas hipoeutéticas do sistema AI-Sn e três ligas hipoeutéticas do sistema AI-Si foram submetidas a solidificação unidirecional, na direção vertical e sentido ascendente, sob condições transitórias de fluxo de calor. Os espaçamentos dendríticos primários (À1) e secundários (À2) foram medidos nas direçõe.s transversal e longitudinal dos lingotes, respectivamente, e correlacionados com as variáveis térmicas que atuaram durante a solidificação. Uma abordagem teórico-experimental foi desenvolvida para determinar quantitativamente_as variáveis térmicas, tais como: coeficiente de transferência de calor na interface metal/molde, velocidade de deslocamento da isoterma liquidus, gradientes térmicos, taxa de resfriamento e tempo local de solidificação. Este estudo também aborda a influência do teor de soluto nos espaçamentos dendríticos das ligas estudadas. Os dados experimentais obtidos, concementes à solidificação das ligas AI-Sn, são comparados com modelos de crescimento dendrítico existentes na literatura. O comportamento mecânico das ligas AI-Sn e AI-Si foi analisado por meio de ensaios de tração e de desgaste. O ensaio de desgaste utilizado foi o ensaio de micro-abrasão por esfera rotativa fixa, sob condições a seco (sem óleo lubrificante ou solução abrasiva). As amostras submetidas aos ensaios de desgaste foram retiradas na direção transversal dos lingotes. A condição a seco foi adotada para impedir a interferência de elementos interfaciais na resposta da microestrutura com relação ao desgaste mecânico. O volume de desgaste é o parâmetro quantificador da resistência ao desgaste e, são obtidas equações que correlacionam o volume de desgaste com espaçamentos dendríticos, levando em consideração o tempo de ensaio, que está relacionado com a distância de deslizamento.
Abstract: The search for relationships between microstructural parameters and mechanical behavior of alloys is fundamental for the pre-programming of final properties of as-cast components. The present study aims to contribute to the understanding about the influence of microstructural parameters on the wear resistance and mechanical properties of alloys of two binary systems: Al-Sn and AI-Si. Such alloys are widely used in engineering applications, especially as bearing components such as journal bearings and cylinder liners, respectively. Despite the wide use of Al-Sn alloys as bearing materiaIs studies on the microstructural development of such alloys are rare.. In the present study, four Al-Sn and three AI-Si hypoeutectic alloys were directionally solidified under upward unsteady state heat flow conditions. The primary (1,,1) and secondary (Â.2) dendrite arm spacings were measured along the castings length and correlated with transient solidification thermal variables. A combined theoretical and experimental approach has been used to quantitatively determine such thermal variables, i.e., transient metaVmold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidifÍcation time. This study also focuses on the dependence of dendrite arm spacings on the alloy solute content. Furthermore, the experimental data conceming the solidification of AI -Sn alloys are compared with the main predictive dendritic models from the literature. The mechanical behaviors ofthe AI-Sn and AlSi alloys were analyzed by wear and tensile tests. Micro-abrasive wear tests under dry sliding conditions and by using a fixed rotating sphere were applied to transversal samples collected along the casting. The dry condition is adopted to prevent effects of interfacial elements such as abrasive slurry or lubricant oil on the microstructural response during the tests. The wear volume was used to evaluate the wear resistance. Afterwards, equations correlating the wear volume and the dendritic arm spacing have been proposed taking into account the influence of time (sliding distance).
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica

Much study has been carried out to determine the properties of Lamellar Graphite Iron (LGI) or grey iron and their relations to factors such as the cooling rate, the dendrite morphology, the pouring temperature, and so on. However, there hasn’t been much comprehensive study on the properties of LGI outside the generally used and accepted composition, with 1 to 3% Silicon. The scope of this study is to measure and evaluate the thermal conductivity and tensile strength of LGI, for a higher concentration of  Si and different carbon contents. The concentration of Si aimed for was 4% but the concentration obtained after spectroscopy was between 4.1% to 4.15%. There are two hypereutectic, one near-eutectic and three hypoeutectic samples considered and these six chemical compositions were cast under different cooling conditions . The cooling time has been varied by providing different molds of 30mm, 55mm, and 80mm diameter cylinders respectively, for all the six sample compositions. The microstructure analysis carried out studies the segregation of Si, the graphite morphology, primary austenite morphology. These factors are then compared to the thermal and tensile behavior measured in this study. It can be observed that the thermal conductivity studied in the present work has a direct correlation for a higher Si content and tends to be greater than the thermal conductivity values observed from other studies with lower content Of Si. However, the conductivity shows an inverse relation with the cooling rate and is maximum for the samples with the lowest cooling rate. The tensile strength, on the other hand, seems to have a lower value than that observed in previous studies for LGI with 1 to 3% Si, but shows a direct correlation with the cooling rate. The mean area fraction of dendrites obtained and the mean interdendritic hydraulic diameter is also measured and their influence on the properties are also studied. The addition of more Si has greatly favored the thermal behavior positively but has also reduced the tensile strength.

Nous avons étudié in situ et en temps réel la solidification dirigée d'échantillons minces d'alliages binaires et d'un quasicristal en combinant radiographie et topographie X. Sur Al-3,5%pdsNi non-affiné, nous avons étudié la formation de l'état initial et la morphologie du front de solidification (croissance cellulaire puis dendritique). Les effets des contraintes mécaniques ont été mis en évidence. La transition colonnaire-équiaxe a été étudiée sur Al-3,5%pdsNi affiné. Nous avons décrit le blocage du front colonnaire et le régime de croissance équiaxe ultérieure. L'efficacité des affinants tend vers une limite. Une analyse de la morphologie des microstructures a été effectuée. L'étude du quasicristal i-AlPdMn montre la croissance de grains dodécaédriques facettés. Nous avons mis en évidence les effets de la convection thermosolutale. La visualisation des contraintes montre une forte déformation des grains. L'apparition de porosités a été observée au cours de la fusion des grains.

La croissance cristalline de cucl 2, 2h 2o par evaporation en presence d'impuretes de type biologique donne naissance a une structure dendritique quasi-bidimensionnelle dont l'image est caracteristique des impuretes introduites. L'analyse de la cinetique de ces croissances cristallines, par analyse d'images, permet l'extraction d'une structure de croissance proche de la structure reelle a partir de laquelle des informations topologiques, geometriques et cinetiques sont accessibles. Apres avoir defini brievement les protocoles physique et chimique, ce memoire presente la methode d'acquisition des images de cristallisation. Puis, deux solutions au probleme de la segmentation d'images sont proposees, l'une basee sur une approche statique l'autre sur une approche dynamique. La determination de la structure de la cristallisation est ensuite proposee en utilisant le contour de l'objet segmente pour detecter, a chaque iteration, les sommets des dendrites. Un algorithme de correspondance de points permet alors de relier les sommets representant une meme dendrite a differents stades de croissance. Une structure de croissance issue de l'analyse dynamique est ainsi disponible. Un ensemble de parametres peuvent ensuite en etre extraits. Enfin, apres avoir decrit les facteurs influencant les croissances cristallines en general, et les cristallisations de cucl 2, 2h 2o en particulier, ce memoire se conclut sur une analyse des parametres extraits de la structure qui revele plusieurs comportements de croissance.

Analyse de l'evolution de la macrostruture et de la microstruture des alliages de fonderie aluminium-silicium as7g en fonction de la composition, des conditions de solidification et des traitements thermiques. L'etude de la macrostruture s'est faite a partir de la reconstruction des zones eutectiques en utilisant des transformations morphologiques et en respectant les conditions de la connaissance locale simple. Quantification de la macrostructure a partir des analyses granulometriques et stereologiques. L'analyse de la microstructure est realisee a partir d'une etude globale de la forme des particules, de silicium. Mise au point et etude critique des procedures d'analyse automatique d'images

D.Phil. (Chemistry)
The application of dendritic-based materials has attracted great interest. For the first time this research has investigated the feasibility of poly (propyleneimine) (PPI) dendrimers and hyperbranched polyethyleneimine (HPEI) in combination with beta-cyclodextrin (β-CD) embedded in polysulfone (PSf) membrane for water treatment. The advantage of embedding these conjugates (β-CD-PPI and β-CD-HPEI) in PSf membranes is the presence of numerous nanocavities which can act as water channels allowing easy water passage through the membrane improving water permeability. Secondly, the presence of functional groups such as –OH and –NH greatly improves hydrophilicity of membranes. Commercial polysulfone (PSf) ultrafiltration membranes were crosslinked with β-cyclodextrin-poly (propyleneimine) (β-CD-PPI) and β-cyclodextrin-hyperbranched polyethyleneimine (β-CD-HPEI) using trimesoyl chloride (TMC) by interfacial polymerisation. These membranes were used in the rejection of Aldrich humic acid (molecular weight: 4.1 kDa) from synthetic water samples prepared in the laboratory. Moreover, β-cyclodextrin-poly (propyleneimine) (β-CD-PPI) was used as a host for the preparation of Fe/Ni nanoparticles. The new membranes were synthesised by crosslinking β-CD-PPI with trimesoyl chloride and subsequently loading Fe/Ni nanoparticles and this was supported on a commercial polysulphone (PSf) layer for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP). The membrane surfaces were characterised using Fourier transform infrared/attenuated total reflectance (FT-IR/ATR) spectroscopy , scanning electron microscopy (SEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HR-TEM), water-contact angle, and water-intake capacity...

Hyaluronic acid (HA) is one of the primary chemical building blocks of the extracellular matrix and thus is an attractive material for biomedical applications. FDA approved HA-based materials are available as dermal fillers, joint viscosupplements, vitreous substitutes, and abdominal adhesion barriers. The engineering of new HA-based materials and applications is an active area of research. Here we develop several new types of HA-based hydrogels with unique and useful properties. To address the challenge of delivering hydrophobic drugs from hydrophilic hydrogel matrices we have grafted HA hydrogels with [Beta]-cyclodextrin to create hydrogels capable of binding poorly water soluble drugs. To create HA hydrogels with unique anisotropic swelling behavior we have developed a dual-crosslinking technique in which a super-swelling chemically crosslinked hydrogel is patterned with low-swelling photocrosslinked domains. When this dual-crosslinked hydrogel is swelled it contorts into a new shape because of differential swelling among photopatterned regions. To address the challenge of creating hydrogel scaffolds with biomimetic branched porosity we have invented a "crystal templating" technique. This technique grows dendritic crystals throughout a biopolymer solution, crosslinks the biopolymer around the crystals, and washes the crystals away to yield a hydrogel with a dendritic macroporous network. Lastly, we invented a method for patterning a substrate with a microarray of hydrogel compartments. A microarray of living cells is obtained when cells are seeded on the hydrogel patterned substrate. This method addresses the need for an inexpensive, simple method for obtaining living cell microarrays that does not require clean room labs and lithographic expertise. Each of these new materials were based on hyaluronic acid hydrogels but the methods are generalizable to hydrogels of other polymers too. In conclusion, the novel methods in this dissertation are a significant contribution to the engineering of HA-based materials.
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Understanding the fundamental mechanisms of solidification and the relative significance of different parameters governing these mechanisms is of vital importance for controlling the evolution of microstructure during solidification, and consequently, for improving the efficacy of a casting process. Towards achieving this goal, the present work attempts to study the effect of convection and shrinkage on solidification and microstructure formation primarily through the development of computational models which are complemented with experimental investigations and analytical solutions. Convection strongly influences the solutal and thermal distribution adjacent to the solidification interface and affects the growth rate and morphology of dendrites. To investigate this, a numerical model based on the enthalpy method is developed for binary alloy dendrite growth in presence of convection. The model results are validated with corresponding predictions using level-set method and micro-solvability theory. Subsequently, the model is applied for studying the effect of convection on the growth morphology of single dendrites. Results show that the presence of flow significantly affects the thermo-solutal distribution and consequently the growth rate and morphology of dendrites. Parametric studies performed using the model predict that thermal and solutal Peclet number and melt undercooling strongly influence the tip velocity of dendrites. Additionally, an analytical model is developed to quantify the effect of convection on dendrite tip velocity through the definition of an equivalent undercooling. An expression for this equivalent undercooling is derived in terms of the flow Nusselt and Sherwood numbers and the analytical equivalent undercooling values are compared with corresponding predictions obtained using the numerical model. Subsequently, the interaction of multiple dendrites growing in close proximity is studied. It is observed that the presence of neighbouring dendrites strongly influences the thermo-solutal distribution in the domain leading to significant changes in growth pattern. The effect of seed density on the growth morphology is investigated and it is observed that a higher initial seeding density leads to more spherical dendritic structure. Comparison with results from chilled casting of Al-6.5% Cu alloy with and without grain refiners show qualitative similarity in both the cases. The next part of the thesis presents a eutectic solidification model developed using the general enthalpy-based framework for dendritic solidification. New parameters and rules are defined and suitable modifications are made to incorporate the physics of eutectic solidification and account for the additional complexities arising due to the presence of multiple solid phases. The model simulates the presence of buoyancy driven convection and its interaction with the solidification process. i The model predictions are found to be in good agreement with the Jackson-Hunt theory. At first, the model is applied to simulate regular eutectic growth in a purely diffusive environment and it is observed that the model predicts the variation in interface profile with change in lamella width similar to those observed in experimental studies on eutectic solidification. Subsequently, a few case studies are performed to demonstrate the ability of the model in handling complex scenarios of eutectic growth such as width selection, lamella division and presence of solutal buoyancy. It is observed that solutal buoyancy gives rise to flow cells ahead of the eutectic interface facilitating the transfer of solute between the two phases. Apart from forced and natural convection, another important factor affecting solidification is the presence of shrinkage. Currently, solidification shrinkage is mostly modelled using empirical relations and criteria functions. In the present work, a phenomenological model for shrinkage driven convection is developed by incorporating the mechanism of solidification shrinkage in an existing framework of enthalpy based macro-scale solidification model. The effect of shrinkage flow on the free surface deformation is accounted for by using the volume-of-fluid method. The results predicted by the model are found to be in excellent agreement with analytical solutions for one-dimensional solidification with unequal phase densities. A set of controlled experiments are designed and executed for validating the numerical model. The experiments involve in-situ X-ray imaging of casting of pure aluminium in a rectangular cavity. The numerical predictions for solidification rate, free surface movement and temperature profiles are compared with corresponding experimental results obtained from the in-situ X-ray images and thermocouple data. Subsequent case studies, performed using the model, show significant influence of applied heat flux and mould geometry on the formation of shrinkage cavities. The shrinkage flow model provides the foundation for development of a generalized model to accurately predict the formation and morphology of internal porosity. The validated macro-scale shrinkage model is extended to the microscopic scale to study the influence of shrinkage flow on the growth rate of dendrites. Results demonstrate that shrinkage driven convection towards the dendrite strongly influences the solutal and thermal distribution adjacent to the solidification interface and consequently decreases the growth rate of the dendrite. Additionally, an analytical model is developed to quantify the effect of shrinkage driven convection through the definition of an equivalent undercooling for shrinkage flow. The present models provide significant physical insight into various mechanisms governing the process of solidification. Moreover, due to their similar framework, the individual models have the potential to be an effective foundation for the development of a generalized multi-scale solidification model incorporating the presence of important phenomena such as shrinkage and convection.

Cracking in continuous casting has always been one of the main problems of steel mills. Many cracks that occur during solidification are difficult to observe from outside the industrial mold. In order to better understand the formation of this defect, compared with the large-scale simulation used in the entire industrial process, microsimulation is also essential. A comprehensive study of using phase field method to simulate microstructure evolution has been conducted. A variety of two-dimensional models based on phase-filed method has been developed in order to simulate dendrites growth in continuous casting process. The basic concepts of phase-field method are presented. Among those models, Kobayashi model was first introduced to describe the morphology of pure material solidification, in this article, which are pure water and pure iron. In order to get closer to the actual situation of continuous casting, a multi-component model was introduced to solve the problem. To go a step further, by introducing a series of temperature parameters and modifications to a series of terms, the binary alloy directional solidification model was used to simulate the process of dendrite growth in continuous casting. Furthermore, the detailed derivation of the binary alloy solidification model and how to apply the model in open source software will also be introduced in this article. The effects of physical parameters such as anisotropic strength, temperature gradient and cooling rate on the growth and evolution of the dendrite interface were quantitatively analyzed. Finally, potential improvement of this model, optimization to primary cooling section in continuous casting process and various applications of the simulation were discussed.

Tesis (Lic. en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2021.
Las baterías con ánodos de litio metálico se presentan como un prometedor sistema para el almacenamiento de energía debido a las múltiples ventajas que este material ofrece. Luego de varios ciclos electroquímicos de carga y descarga, se forman microestructuras en la superficie del electrodo de litio metálico, llamadas dendritas. Estas ramificaciones pueden ocasionar un cortocircuito que derivan en descargas espontáneas, volviéndolas inseguras. La caracterización de estas microestructuras contribuye al desarrollo para encontrar alternativas con fin de evitar los inconvenientes que éstas producen. En este trabajo se presenta un estudio teórico del efecto de la morfología de las microestructuras en los espectros de Resonancia Magnética Nuclear. Las simulaciones se llevaron a cabo mediante herramientas numéricas basadas en el método de elemento finito, utilizando un algoritmo que permite calcular las variaciones de campo magnético inducido por una distribución de susceptibilidad de un objeto.
Lithium metal is a promising anode material for rechargeable batteries due to its properties such as high theoretical specific capacity and low weight. After several electrochemical cycles of charge and discharge, microstructures, called dendrites, are formed on the surface of the metallic lithium electrode. These microstructures may cause a short circuit resulting in spontaneous discharges, making the batteries unsafe. The characterization of these microstructures contributes to the development to find alternatives in order to avoid the inconveniences that they produce. In this work, a theoretical study of the effect of the morphology of the microstructures in the Nuclear Magnetic Resonance spectrum is presented. Simulations were carried out using numerical tools based on the finite element method, using an algorithm that allows the calculation of the susceptibility-induced field-shift of an object with known susceptibility distribution.
Fil: Zampieri, Muriel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.

碩士
國立臺灣大學
生物產業機電工程學研究所
103
This research is dedicating to one of the most promising lithium metal battery, lithium sulfur battery. The development of this kind of lithium metal battery is facing some challenges recently, which can split to two parts. One of them is dendrite growth on the lithium metal negative electrode, which may cause some safety issue, including short-circuited and energy capacity decay. We designed a symmetric cell to in-situ observe dendrite growth when applying a constant current. In order to study the relationship between mechanical strength and dendrite growth, we fabricated the cell with different gel polymer electrolyte with different Young’s modulus. We found that when using the gel polymer electrolyte which Young’s modulus is 0.05548MPa and the current density is 0.1mA/cm2, dendrite would not grow in the first 3000 minutes. We also found that the mechanism of oxidation of lithium metal is very similar to pitting corrosion. When using the electrolyte which diffusivity is lower, the phenomena of pitting corrosion is less apparent. The other part is the dissolution of sulfur electrode. Due to its physic properties, the lithium sulfide would gradually dissolve into the electrolyte. This may cause some energy capacity decay. We add an additional layer into the cell to be a protect layer. This layer could efficiently adsorb the lithium sulfide that dissolved into the solution, reducing the decay rate of the cell. We also mixed MWCNT with carbonized lignin, and found that 50% 900℃ carbonized lignin MWCNT film could make the cell remain 1000mAh/g S capacity after 60 cycles(0.1C).

abstract: Counterfeiting of goods is a widespread epidemic that is affecting the world economy. The conventional labeling techniques are proving inadequate to thwart determined counterfeiters equipped with sophisticated technologies. There is a growing need of a secure labeling that is easy to manufacture and analyze but extremely difficult to copy. Programmable metallization cell technology operates on a principle of controllable reduction of a metal ions to an electrodeposit in a solid electrolyte by application of bias. The nature of metallic electrodeposit is unique for each instance of growth, moreover it has a treelike, bifurcating fractal structure with high information capacity. These qualities of the electrodeposit can be exploited to use it as a physical unclonable function. The secure labels made from the electrodeposits grown in radial structure can provide enhanced authentication and protection from counterfeiting and tampering. So far only microscale radial structures and electrodeposits have been fabricated which limits their use to labeling only high value items due to high cost associated with their fabrication and analysis. Therefore, there is a need for a simple recipe for fabrication of macroscale structure that does not need sophisticated lithography tools and cleanroom environment. Moreover, the growth kinetics and material characteristics of such macroscale electrodeposits need to be investigated. In this thesis, a recipe for fabrication of centimeter scale radial structure for growing Ag electrodeposits using simple fabrication techniques was proposed. Fractal analysis of an electrodeposit suggested information capacity of 1.27 x 1019. The kinetics of growth were investigated by electrical characterization of the full cell and only solid electrolyte at different temperatures. It was found that mass transport of ions is the rate limiting process in the growth. Materials and optical characterization techniques revealed that the subtle relief like structure and consequently distinct optical response of the electrodeposit provides an added layer of security. Thus, the enormous information capacity, ease of fabrication and simplicity of analysis make macroscale fractal electrodeposits grown in radial programmable metallization cells excellent candidates for application as physical unclonable functions.
Dissertation/Thesis
Masters Thesis Materials Science and Engineering 2017

The hybrid nanostructures exhibit excellent performances in various fields such as catalysis, sensing, and energy conversion as compared to their individual ones. The thesis deals with the new methods for the synthesis of different type of hybrids with doped/pristine carbon nanostructures in the form of graphene, multiwall carbon nanotubes (MWCNTs) as one component and metals nanostructures (Ag, Pd, Pt and Au), carbide (Fe3C), metal chalcogenides (Ni3S2 and Co9S8) and oxide (CoO) as the other components. Various synthesis techniques such as modified galvanic replacement reaction at room temperature, hydrothermal, microwave and pyrolysis have been explored for the synthesis of different hybrid nanostructures. Furthermore, various hybrid nanostructures have been explored for various catalytic activities such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and 4-nitrophenol (4-NP) reduction. It may be noted that the ORR and OER which are undoubtedly vital for their applications in fuel cells, metal-air batteries and water oxidation reaction. Interestingly, the catalytic activities of these hybrid nanostructures are comparable or better as compared to the commercial benchmark precious catalysts.

Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.

Plastic flow in bulk metallic glasses (BMGs) localizes into narrow bands, which, in the absence of a microstructure that could obstruct them, propagate unhindered under tensile loading. In constrained deformation conditions such as indentation and at notch roots, extensive shear band formation can occur. A key issue in the context of fracture of BMGs that is yet to be understood comprehensively is how their toughness is controlled by various state parameters. Towards this end, the change in fracture toughness and plasticity with short term annealing above and below the glass transition temperature, Tg, is studied in a Zr-based BMG. Elastic properties like shear modulus, Poisson's ratio as well as parameters defining the internal state like the fictive temperature, Tf, density, and free volume are measured and correlation with the toughness was attempted at. While the elastic properties may help in distinguishing between tough and brittle glasses, they fail to reveal the reasons behind the toughness variations. Spherical-tip nanoindentation and microindentation tests were employed to probe the size, distributions and activation energies of the microscopic plastic carriers with the former and shear band densities with the latter. Results indicate that specimens annealed at a higher temperature, Ta, exhibit profuse shear banding with negligible changes in the local yield strengths. Statistical analysis of the nanoindentation data by incorporating the nucleation rate theory and the results of the cooperative shear model (CSM), reveals that short term annealing doesn't alter the shear transformation zone (STZ) size much. However, density estimates indicate changes in the free volume content across specimens. A model combining STZ activation and free volume accumulation predicts a higher rate in the reduction of the cumulative STZ activation barrier in specimens with a higher initial free volume content. Of the macroscopic physical properties, the specimen density is revealed to be a useful qualitative measure of enhancement in fracture toughness and plasticity in BMGs. We turn our attention next to the brittle fracture in BMGs, with the specific objective of understanding the mechanisms of failure. For this purpose, mode I fracture experiments were conducted on embrittled BMG samples and the fracture surface features were analyzed in detail. Wallner lines, which result from the interaction between the propagating crack front and shear waves emanating from a secondary source, were observed on the fracture surface and geometric analysis of them indicates that the maximum crack velocity to be ~800 m/s, which corresponds to ~0.32 times the shear wave speed. Fractography reveals that the sharp crack nucleation at the notch tip occurs at the mid-section of the specimens with the observation of flat and half-penny shaped cracks. On this basis, we conclude that the crack initiation in brittle BMGs occurs through hydrostatic stress assisted cavity nucleation ahead of the notch tip. High magnification scanning electron and atomic force microscopies of the dynamic crack growth regions reveal highly organized, nanoscale periodic patterns with a spacing of ~79 nm. Juxtaposition of the crack velocity with this spacing suggests that that the crack takes ~10-10 s for peak-to-peak propagation. This, and the estimated adiabatic temperature rise ahead of the propagating crack tip that suggests local softening, are utilized to critically discuss possible causes for the nanocorrugation formation. The Taylor’s fluid meniscus instability is unequivocally ruled out. Then, two other possible mechanisms, viz. (a) crack tip blunting and resharpening through nanovoid nucleation and growth ahead of the crack tip and eventual coalescence, and (b) dynamic oscillation of the crack in a thin slab of softened zone ahead of the crack-tip, are critically discussed. One way of alleviating the fracture-related issues in BMGs is to impart a microstructure to it, which would either impede the growth of shear bands or promote the multiplication of them. One such approach is through the BMG composites (BMGCs) route, wherein a crystalline second phase incorporated in the BMG matrix. There is a need to study the effects of reinforcement content, size and distribution on the mechanical behavior of the BMGC so as to achieve an optimum combination of strength and ductility. For this purpose, an investigation into the microstructure and tensile properties of Zr/Ti-based BMG composites of the same composition, but produced by different routes, was conducted so as to identify “structure–property” connections in these materials. This was accomplished by employing four different processing methods—arc melting, suction casting, semi-solid forging and induction melting on a water-cooled copper boat—on composites with two different dendrite volume fractions, Vd. The change in processing parameters only affects microstructural length scales such as the interdendritic spacing, λ, and dendrite size, δ, whereas compositions of the matrix and dendrite are unaffected. Broadly, the composite’s properties are insensitive to the microstructural length scales when Vd is high (∼75%), whereas they become process dependent for relatively lower Vd (∼55%). Larger δ in arc-melted and forged specimens result in higher ductility (7–9%) and lower hardening rates, whereas smaller dendrites increase the hardening rate. A bimodal distribution of dendrites offers excellent ductility at a marginal cost of yield strength. Finer λ result in marked improvements in both ductility and yield strength, due to the confinement of shear band nucleation sites in smaller volumes of the glassy phase. Forging in the semi-solid state imparts such a microstructure.

Dans le domaine de l'élaboration des alliages métalliques, les principaux enjeux industriels résident dans la possibilité de maîtriser la structure métallurgique ainsi que les défauts qui surviennent lors de la phase de solidification. Lors de la solidification, les mouvements hydrodynamiques dans la phase liquide ont une influence importante sur les propriétés du produit solidifié. Dans cette étude, la conception d'un nouveau dispositif BATMAF (Bridgman Apparatus with a Travelling MAgnetic Field) constitué d'un four de solidification dirigée et d'une bobine de Bitter permettant de produire un champ magnétique glissant a permis d'étudier l'influence d'une convection forcée sur la solidification dirigée des alliages métalliques binaires. Notre attention s'est plus particulièrement portée sur deux effets majeurs influencés par la présence de convection forcée ou non : la macroségrégation et la structure de grains pour un alliage d'Al-3.5%pdsNi en présence ou non de particules affinantes. La vitesse ainsi que le sens de l'écoulement forcé peuvent être contrôlés par l'application du champ magnétique glissant. Nous avons montré que dans le cas de notre alliage, la macroségrégation peut-être contrôlée et que de plus, l'espacement primaire dendritique est modifié en fonction du champ appliqué. En ce qui concerne les structures de grains, à l'aide d'un modèle analytique, nous montrons que l'extension de la couche solutale en avant du front de solidification varie en fonction du sens de l'écoulement au voisinage de la zone pâteuse. Ceci conditionne la possibilité pour les grains équiaxes de germer puis de croître et, par conséquent, l'obtention du régime équiaxe ou non. Enfin, dans le cas des alliages non affinés, dans un domaine d'intensité de brassage, un régime de grains libres allongés a pu être obtenu probablement par fragmentation. Cette étude démontre s'il en était besoin, l'importance cruciale de la maîtrise de la convection sur les macroségrégations et la structure des grains et ouvre des perspectives quant à l'utilisation du champ magnétique glissant pour leur contrôle