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1
Wackerow, Stefan. "Fabrication and characterisation of silver-glass nanocomposites." Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/1371615f-51ae-4210-bc46-c13c0199f478.
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Metallic nanoparticles and nanostructures have spawned significant interest in a wide area of science. Nanoparticles in glass show unique linear and nonlinear optical properties due to surface plasmon resonances. These induce absorption and scattering of light around the resonance wavelength, which can be tuned by changing size, shape or spatial distribution of the nanoparticles. Metallic nanostructures show local field enhancement effects, which are used for example in surface enhanced Raman scattering. Their large surface area compared to bulk materials makes them interesting for applications in chemistry and life science. In this thesis the synthesis of two different types of silver-glass nanocomposites is investigated. Both materials are prepared from silver ion-exchanged glass, which is also prepared and characterised in house. The first type of nanocomposite is glass doped with silver nanoparticles. It is formed by annealing silver ion-exchanged glass at a temperature close to the transition point. This induces the reduction of silver to atoms and the agglomeration in nanoparticles with a diameter of less than 10nm, which are located in a layer beneath the glass surface, which has a thickness of tens of micrometres. These nanoparticles are responsible for a characteristic absorption band centred around 410nm due to plasmon resonances. The second nanocomposite, which was first produced in the course of this work, is called glass-silver composite. It is created by pulsed laser irradiation of silver ion-exchanged glass. It contains nanoparticles with a diameter of 100nm or more, which are distributed homogeneously in a dense single monolayer at the glass surface. This material shows a strong metal-like reflection of light. The location of nanoparticles at the surface makes it interesting for applications utilising the field enhancement effect of the nanoparticles, such as surface enhanced Raman scattering and enhancement of light conversion. Both nanocomposites and the ion-exchanged glass are characterised by optical microscopy, scanning electron microscopy and optical spectroscopy. The work is divided in four chapters, starting with an introduction in chapter 1. In chapter 2 the method of production of the silver ion-exchanged glass and the properties of the material are presented. Generation of nanoparticles inside the glass by annealing is covered in chapter 3 and an analysis of laser processing of ion-exchanged glasses is shown in chapter 4. The concluding chapter consists of a summary of the work and an outlook.
2
Bhardwaj, Mohit. "Water vapor diffusion through glass fiber reinforced polymer nanocomposites." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4193.
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Thesis (M.S.)--West Virginia University, 2005.<br>Title from document title page. Document formatted into pages; contains x, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 116-118).
3
Qureshi, Muhammad Asif Mahmood. "Glass-fiber reinforced polymer-clay nanocomposites in structural applications." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10557.
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Thesis (M.S.)--West Virginia University, 2009.<br>Title from document title page. Document formatted into pages; contains xi, 71 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 69-71).
4
Tong, Wan. "Characterisation of PA/clay nanocomposite and glass fibre filled PA/clay nanocomposites." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439857.
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Tang, Guang. "Nanosecond pulsed laser processing of metals and welding of metal-glass nanocomposites." Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/9b39b598-92e3-4118-bc99-034a360e8e3d.
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In this thesis, nanosecond pulsed lasers are used as the tools to generate microstructures on metal and glass. The applications of these structures are described too. The production of micro structures is demonstrated using diode-pumped solid state (DPSS) Nd:YVO4 lasers operating at wavelengths of 532nm or 1064 nm. The laser fluence and scanning speed are important parameters to control the results. The first part of thesis is on the laser generation of microstructures on metal surfaces. Copper (Cu) and titanium (Ti) have been studied. According to the reflectivity of metals, Cu is processed by a 532nm laser and Ti is processed by a 1064nm laser. It is shown that the periods of surface microstructures are highly dependent on the hatch distance (overlapping distance between laser scanning). Only if the laser fluence is greater than a threshold, may the microstructures on metals be induced. The thresholds are measured by the diameters of ablated areas at different fluence. Laser generated surface microstructures have been applied to modify the reflectivity of a Cu sample. It was found that laser induced surface microstructures on Copper can decrease the surface reflectivity by almost 97% between 250 nm and 700 nm. To find the mechanism of how to form microstructure on metal surface with laser, laser ablation and heating models have been studied. The 1D ablated numerical model is calculated in Matlab. The pressure of metal vapour is an important parameter, as it pushes the melted metal out of surface to form microstructures after re-solidification. The second part of thesis is on glass welding with microstructures on glass surfaces. The soda-lime glasses containing silver nanoparticles (from the company Codixx) have been studied and welded with Schott B270 glass. Compared with other techniques for welding glass, lasers offer the advantage of a relatively simple and flexible technique for joining the local area underneath the cover glass. Most of the laser energy is deposited in the Ag nanoparticle layer because of the large absorption coefficient at 532 nm. Expanded microstructures generated by the laser are applied to fill the gap between the glass surfaces. This is attributed to the formation of bubbles in the Ag nanoparticle layer after laser processing. The welded samples have the joint strength of 4.9 MPa and have great potential for industrial applications. A 3D analytical model is used to estimate the temperature of the glass after the laser pulse. The increase in temperature is about 129 °C. To induce the bubble in glass, many laser pulses are necessary. This is very different from the results for the metals.
6
Kandasamy, Prabhakar. "Experimental Determination of Mechanical and Wear Performance of Glass Fiber Reinforced Polymer Nanocomposites." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/82465.
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This research work focused to identify the key parameters through systematic approach that influence the interfacial bonding strength between matrix and the glass filler. The enhanced coupling agent of silane due to the nanoclay appropriate concentration interact with the functional groups in the epoxy resin and glass fiber, leads to strong interfacial bonding through the formation of intercalation structure. Henceforth, resulted in increased surface hardness leading improved wear performance of the Glass fiber reinforced nanocomposite.
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Liu, Mingyang. "Improved durability and thermal stability of glass fiber reinforced composites using clay-polymer nanocomposites /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20LIU.
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Porwal, Harshit. "Processing and properties of graphene reinforced glass/ceramic composites." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9107.
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This research provides a comprehensive investigation in understanding the effect of the addition of graphene nano-platelets (GNP) on the mechanical, tribological and biological properties of glass/ceramic composites. We investigated two kinds of materials namely amorphous matrices like glasses (silica, bioglass) and polycrystalline matrices like ceramics (alumina). The idea was to understand the effect of GNP on these matrices as GNP was expected to behave differently in these composites. Bioglass (BG) was also chosen as a matrix material to prepare BG-GNP composites. GNP can improve the electrical conductivity of BG which can be used further for bone tissue engineering applications. The effect of GNP on both electrical conductivity and bio-activity of BG-GNP composites was investigated in detail. There were three main problems for fabricating these novel nano-composites: 1) Production of good quality graphene; 2) Homogeneous dispersion of graphene in a glass/ceramic matrix and; 3) Retention of the graphitic structure during high temperature processing. The first problem was solved by synthesising GNP using liquid phase exfoliation method instead of using a commercially available GNP. The prepared GNP were ~1 μm in length with a thickness of 3-4 layers confirmed using transmission electron microscopy. In order to solve the second problem various processing techniques were used including powder and colloidal processing routes along with different solvents. Processing parameters were optimised to fabricate glass/ceramic-GNP composite powders. Finally in order to avoid thermal degradation of the GNP during high temperature processing composites were sintered using spark plasma sintering (SPS) technique. Fully dense composites were obtained without damaging GNP during the sintering process also confirmed via Raman spectroscopy. Finally the prepared composites were characterised for mechanical, tribological and biological applications. Interestingly fracture toughness and wear resistance of the silica nano-composites increased with increasing concentration of GNP in the glass matrix. There was an improvement of ~45% in the fracture toughness and ~550% in the wear resistance of silica-GNP composites with the addition of 5 vol% GNP. GNP was found to be aligned in a direction perpendicular to the applied force in SPS. In contrast to amorphous materials fracture toughness and scratch resistance of alumina-GNP composites increased only for small loading of GNP and properties of the composites decreased after a critical concentration. There was an improvement of ~40% in the fracture toughness with the addition of only 0.5 vol% GNP in the alumina matrix while the scratch resistance of the composite increased by ~10% in the micro-ductile region. Electrical conductivity of the BG-GNP composite was increased by ~9 orders of magnitude compared to pure BG. In vitro bioactivity tests performed on BG-GNP composites confirmed that the addition of GNP to BG matrix also improved the bioactivity of the nano-composites confirmed using XRD analysis. Future work should focus on understanding electrical and thermal properties of these novel nano-composites.
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Ozkoc, Guralp. "Abs/polyamide-6 Blends, Their Short Glass Fiber Composites And Organoclay Based Nanocomposites: Processing And Characterization." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608266/index.pdf.
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The objective of this study is to process and characterize the compatibilized blends of
acrylonitrile-butadiene-styrene (ABS) and polyamide-6 (PA6) using olefin based
reactive copolymers and subsequently to utilize this blend as a matrix material in short
glass fiber (SGF) reinforced composites and organoclay based nanocomposites by
applying melt processing technique. In this context, commercially available epoxydized
and maleated olefinic copolymers, ethylene-methyl acrylate-glycidyl methacrylate
(EMA-GMA) and ethylene-n butyl acrylate-carbon monoxide-maleic anhydride
(EnBACO-MAH) were used as compatibilizers at different ratios. Compatibilizing
performance of these two olefinic polymers was investigated through blend
morphologies, thermal and mechanical properties as a function of blend composition and
compatibilizer loading level. Incorporation of compatibilizer resulted in a fine
morphology with reduced dispersed particle size. At 5 % EnBACO-MAH, the toughness
was observed to be the highest among the blends produced.
SGF reinforced ABS and ABS/PA6 blends were prepared with twin screw extrusion.
The effects of SGF concentration and extrusion process conditions on the fiber length
distribution, mechanical properties and morphologies of the composites were examined.
The most compatible organosilane type was designated from interfacial tension and
short beam flexural tests, to promote adhesion of SGF to both ABS and PA6. Increasing
amount of PA6 in the polymer matrix improved the strength, stiffness and also
toughness of the composites. Effects of compatibilizer content and ABS/PA6 ratio on
the morphology and mechanical properties of 30% SGF reinforced ABS/PA6 blends
were investigated. The most striking result of the study was the improvement in the
impact strength of the SGF/ABS/PA6 composite with the additions of compatibilizer.
Melt intercalation method was applied to produce ABS/PA6 blends based organoclay
nanocomposites. The effects of process conditions and material parameters on the
morphology of blends, dispersibility of nanoparticles and mechanical properties were
investigated. To improve mixing, the screws of the extruder were modified. Processing
with co-rotation yielded finer blend morphology than processing with counter-rotation.
Clays were selectively exfoliated in PA6 phase and agglomerated at the interface of
ABS/PA6. High level of exfoliation was obtained with increasing PA6 content and with
screw speed in co-rotation mode. Screw modification improved the dispersion of clay
platelets in the matrix.
10
Comer, Anthony C. "DYNAMIC RELAXATION PROPERTIES OF AROMATIC POLYIMIDES AND POLYMER NANOCOMPOSITES." UKnowledge, 2011. http://uknowledge.uky.edu/cme_etds/1.
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The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement.
The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading.
Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.
11
Chen, Kai. "Thermal behavior of model polystyrene materials exploring nanoconfinement effect /." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2009r/chen.pdf.
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Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.<br>Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Derrick R. Dean, Wiliam K. Nonidez, Andrei Stanishevsky, Charles L. Watkins. Includes bibliographical references.
12
Mohan, Sabitha [Verfasser], Gerhard [Akademischer Betreuer] Seifert, Frank [Akademischer Betreuer] Hubenthal, and Ralf [Akademischer Betreuer] Wehrspohn. "Third-order optical nonlinearities of glass-metal nanocomposites / Sabitha Mohan. Betreuer: Gerhard Seifert ; Frank Hubenthal ; Ralf Wehrspohn." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2011. http://d-nb.info/1025301862/34.
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Ruan, Dihui. "Glass Formation Behavior of Model Ionomers." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430242844.
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Barta, Meredith Brooke. "Nanocomposite glass-ceramic scintillators for radiation spectroscopy." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45851.
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In recent years, the United States Departments of Homeland Security (DHS) and Customs and Border Protection (CBP) have been charged with the task of scanning every cargo container crossing domestic borders for illicit radioactive material. This is accomplished by using gamma-ray detection systems capable of discriminating between non-threatening radioisotopes, such as Cs-137, which is often used in nuclear medicine, and fissile material, such as U-238, that can be used to make nuclear weapons or "dirty" bombs. Scintillation detector systems, specifically thallium-doped sodium iodide (NaI(Tl)) single crystals, are by far the most popular choice for this purpose because they are inexpensive relative to other types of detectors, but are still able to identify isotopes with reasonable accuracy. However, increased demand for these systems has served as a catalyst for the research and development of new scintillator materials with potential to surpass NaI(Tl). The focus of a majority of recent scintillator materials research has centered on sintered transparent ceramics, phosphor-doped organic matrices, and the development of novel single crystal compositions. Some of the most promising new materials are glass-ceramic nanocomposites. By precipitating a dense array of nano-scale scintillating crystals rather than growing a single monolith, novel compositions such as LaBr₃(Ce) may be fabricated to useful sizes, and their potential to supersede the energy resolution of NaI(Tl) can be fully explored. Also, because glass-ceramic synthesis begins by casting a homogeneous glass melt, a broad range of geometries beyond the ubiquitous cylinder can be fabricated and characterized. Finally, the glass matrix ensures environmental isolation of the hygroscopic scintillating crystals, and so glass-ceramic scintillators show potential to serve as viable detectors in alpha- and neutron-spectroscopy in addition to gamma-rays. However, for the improvements promised by glass-ceramics to become reality, several material properties must be considered. These include the degree of control over precipitated crystallite size, the solubility limit of the glass matrix with respect to the scintillating compounds, the variation in maximum achievable light yield with composition, and the peak wavelength of emitted photons. Studies will focus on three base glass systems, sodium-aluminosilicate (NAS), sodium-borosilicate (NBS), and alumino-borosilicate (ABS), into which a cerium-doped gadolinium bromide (GdBr₃(Ce)) scintillating phase will be incorporated. Scintillator volumes of 50 cubic centimeters or greater will be fabricated to facilitate comparison with NaI(Tl) crystals currently available.
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Mohamed, Fathia [Verfasser], and Ernst [Akademischer Betreuer] Roessler. "Dynamics of Advanced Polymer Systems studied by Dielectric Spectroscopy and Rheology: From Binary Glass Formers to Nanocomposites / Fathia Mohamed ; Betreuer: Ernst Roessler." Bayreuth : Universität Bayreuth, 2018. http://d-nb.info/1161007369/34.
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Kayiplar, Burcu. "Microwave Sintering And Characterization Of Alumina And Alumina Matrix Ceramic Nanocomposites." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611854/index.pdf.
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ABSTRACT
MICROWAVE SINTERING AND CHARACTERIZATION OF ALUMINA
AND ALUMINA MATRIX CERAMIC NANOCOMPOSITES
Kayiplar, Burcu
M.S., Department of Metallurgical and Materials Engineering
Supervisor: Assist. Prof. Dr. Arcan F. Dericioglu
April 2010, 106 pages
Efficiency of microwave heating on the sintering of ceramic materials has been
investigated in comparison to conventional processing. Monolithic alumina with or
without sintering additives such as MgO, CaO, Y2O3 were fabricated by both
conventional and microwave sintering at temperatures ranging from 1000°<br>C to
1600°<br>C with a constant soaking time of 1 hour. Based on the densification results
on monolithic alumina, nanometer-sized SiC or stabilized ZrO2 particle-dispersed
alumina matrix ceramic nanocomposites were sintered by both methods at 1300°<br>C
and 1500°<br>C for 1 hour. Sintered ceramic materials were characterized in terms of
densification, microstructural evolution, chemical composition and mechanical
properties such as hardness and indentation fracture toughness.
Microwave sintering was determined to be a remarkably effective method in the
production of Al2O3 ceramics at considerably low temperatures (&<br>#8804<br>1400°<br>C)
compared to conventional sintering in achieving enhanced relative densities
reaching to ~97% with improved microstructural characteristics and mechanical
properties. Usage of sintering additives at temperatures higher than 1400°<br>C was
determined to be effective in densifiying Al2O3 by both methods. Second phase
particle incorporation yielded poor densification resulting in a decrease of
hardness of the fabricated ceramic nanocomposites<br>however, their fracture
toughness improved considerably caused by the crack deflection at the dispersed
particles and grain boundaries reaching to ~4 MPa·<br>m1/2 in the case of SiC particledispersed
nanocomposites. Compared to conventional sintering, microwave
sintering is more effective in the processing of alumina and alumina matrix
nanocomposites leading to similar densification values along with improved
microstructural and mechanical characteristics at lower temperatures in shorter
soaking periods.
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Pistor, Vinicius. "Influência da adição do oligômero poliédrico de silsesquioxano-poss-n-fenilaminopropil nas propriedades físicas da resina epoxídica." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/88553.
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As resinas termorrígidas são uma classe de polímeros que devido à reação de reticulação deveriam apresentar uma única cadeia molecular de peso infinito, no entanto, questionamentos sugerem que a formação da rede tridimensional é não-homogênea. Atualmente, devido aos avanços obtidos pela nanotecnologia, torna-se possível uma abordagem diferenciada na modificação química de polímeros como a resina epoxídica. Neste trabalho, foram preparados nanocompósitos adicionando diferentes teores do oligômero poliédrico de silsesquioxano (POSS) n-fenilaminopropil na resina epoxídica. Foi substituindo 1, 5 e 10 por cento em massa (% m.) do agente de reticulação trietilenotetramina (TETA) por POSS. Esta modificação foi realizada com o objetivo de promover maior concentração de interligações nas interfaces das regiões nodulares, descritas como imperfeições ou descontinuidades que ocorrem pela cura não-homogênea da resina. Através da morfologia e da análise do teor de gel, foi evidenciada boa dispersão e melhoria na homogeneidade da rede tridimensional da resina acima de 5 % m. de POSS e aumento da fração gel nos nanocompósitos comparados com a resina epoxídica pura. Na realização de análises de difração de raio-x (DRX) foi visto que a adição do POSS aumentou a distância média entre as cadeias da resina. Foi realizada análise dinâmico-mecânica (DMA) no modo não-isotérmico e por varredura de frequência no modo isotérmico. Pelo modo não-isotérmico os resultados demonstraram que o POSS deslocou a Tg para temperaturas maiores e não alterou significativamente a densidade de ligações cruzadas da resina epoxídica. O modo isotérmico foi utilizado para a determinação de parâmetros das equações de Williams-Landel-Ferry (WLF) e Vogel-Fulcher-Tammann (VFT). Foi calculada a distribuição dos espectros de relaxação H(t) e retardação L(t) molecular através dos módulos de armazenamento e perda obtidos pelo modo isotérmico no DMA. Os parâmetros WLF e VFT demonstraram que a incorporação do POSS ao mesmo tempo em que aumentou a Tg, reduziu a energia de ativação de movimentação segmentar e tornou a resina epoxídica mais forte estruturalmente. A redução da energia de ativação foi associada com a redução das forças de interação intermolecular, enquanto que a redução da fragilidade foi associada ao fato do POSS ser capaz de interligar as interfaces de regiões nodulares. Os espectros H(t) e L(t) mostraram que o pico de relaxação associado aos nódulos formados no processo de reticulação desapareceu. A determinação da capacidade calorífica (Cp) e do excesso de entropia (Sex) através de análises de calorimetria exploratória diferencial modulada (MDSC) demonstrou que o POSS é capaz de minimizar as flutuações de calor ao longo da microestrutura da resina epoxídica. A minimização das flutuações térmicas e a alteração dos tempos de relaxação demonstram que a adição do POSS é eficiente em termos de minimização de imperfeições na microestrutura da resina epoxídica.<br>The thermosetting resins are a class of polymers that due to the crosslinking reaction should present a single chain with infinite molecular weight; however, questions suggest that the formation of three-dimensional network is non-homogeneous. Today, due to advancements in nanotechnology, became possible a differentiated approach in the chemical modification of polymers such as epoxy resin. In this work, nanocomposites with different contents of the polyhedral oligomeric silsesquioxane (POSS) n-phenylaminopropyl in epoxy resin were prepared. It was substituted 1, 5 and 10 weight percent (wt%) of the crosslinking agent, triethylenetetramine (TETA), for POSS. This modification was performed in order to promote greater concentration of interconnections at the interfaces of the regions described as nodular imperfections or discontinuities that arise due to inhomogeneous cure of the resin. Through the morphology and the gel content analysis was observed good dispersion and improvements in the uniformity of three-dimensional network of the resin up till 5 wt% of the POSS and increase in the gel fraction of the nanocomposites compared with pure epoxy resin. X-ray diffraction (XRD) showed that the POSS promoted an increase in distance between chains of the resin. Dynamic-mechanical analysis (DMA) was performed in non-isothermal mode and a frequency sweep in the isothermal mode. By non-isothermal mode the results showed that the POSS shifted the Tg to higher temperatures and does not modify the crosslink density. The isothermal mode was used to determine the parameter of the Williams-Landel-Ferry (WLF) and Vogel-Fulcher-Tammann (VFT) equations. The distribution of the relaxation H(t) and retardation L(t) spectra was calculated through the storage (E') and loss (E'') modulus obtained by the DMA isothermal mode. The WLF and VFT parameters showed that the incorporation of POSS at the same time increased the Tg reduced the activation energy of segmental motion and made the epoxy resin structurally stronger. The reduction in the activation energy was associated with reduced intermolecular forces whereas the decrease in the structural fragility is associated with the fact that the POSS be able to interconnect the interfaces of the nodular regions. The H(t) and L(t) spectra showed that the nodules formed in the crosslinking process disappeared. The determination of the heat capacity (Cp) and excess entropy (Sex), analyzed by modulated differential scanning calorimetry (MDSC), showed that POSS is capable of minimizing fluctuations of heat along the microstructure of the epoxy resin. The reduction of thermal fluctuations and change in the relaxation times shows that the POSS addition is efficient to minimize imperfections in the microstructure of the epoxy resin.
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Xiao, Zhang. "PROBING POLYMER DYNAMICS USING HIGH THROUGHPUT BROADBAND DIELECTRIC SPECTROSCOPY." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1533127319642101.
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Alharbi, Abdulaziz. "Deformation of hexagonal boron nitride." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/deformation-of-hexagonal-boron-nitride(6c6013c4-8c17-4dec-b250-ed3f0baea7ed).html.
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Boron nitride (BN) materials have unique properties, which has led to interest in them in the last few years. The deformation of boron nitride materials including hexagonal boron nitride, boron nitride nanosheets (BNNSs) and boron nitride nanotubes have been studied by Raman spectroscopy. Both mechanical and liquid exfoliations were employed to obtain boron nitride nanostructures. Boron nitride glass composites were synthesised and prepared in thin films to be deformed by bending test in-situ Raman spectroscopy. Hexagonal boron nitride in the form of an individual flake and as flakes dispersed in glass matrices has been deformed and Raman measurement shows its response to strain. The shift rates were, -4.2 cm-1/%, -6.5 cm-1/% for exfoliated h-BN flake with thick and thin regions and -7.0 cm-1/%, -2.8 cm-1/% for the h-BN flakes in the h-BN/ glass (I) and glass (II) composites. Boron nitride nanosheets (BNNSs) shows a G band Raman peak at 1367.5 cm-1, and the deformation process of BNNSs/ glass composites gives a shift rate of -7.65 cm-1/% for G band. Boron nitride nanotubes (BNNTs) have a Raman peak with position at 1368 cm-1, and their deformation individually and in composites gives Raman band shift rates of -25.7 cm-1/% and -23.6 cm-1/%. Glass matrices shows compressive stresses on boron nitride fillers and this was found as an upshift in the frequencies of G band peak of boron nitride materials. Grüneisen parameters of boron nitride (BN) were used to calculate the residual strains in glass matrices of BNNSs nanocomposites as well as to estimate the band shift rates which found to be in agreement with the experimental shift rate of bulk BN and BNNTs.
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Yang, Yong. "Carbon dioxide assisted polymer micro/nanofabrication." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117591862.
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Thesis (Ph. D.)--Ohio State University, 2005.<br>Title from first page of PDF file. Document formatted into pages; contains xviii, 226 p.; also includes graphics (some col.). Includes bibliographical references (p. 206-226). Available online via OhioLINK's ETD Center
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Gnanasekar, Vignesh Kumar. "Evaluation of Thermal Stress in Carbon/Glass Hybrid and Glass Nanocomposite under Resistive Heating." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1450037103.
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Vaddi, Satya. "Flammability evaluation of glass fiber reinforced polypropylene and polyethylene with montmorillonite nanoclay additives." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2009r/vaddi.pdf.
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Thesis (M.S.)--University of Alabama at Birmingham, 2008.<br>Title from PDF title page (viewed Feb. 1, 2010). Additional advisors: Derrick R. Dean, Gregg M. Janowski, Selvum (Brian) Pillay (ad hoc). Includes bibliographical references (p. 76-82).
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Bosq, Nicolas. "Nanocomposites à matrice polymère : influence de silices nanostructurées sur la cristallisation, la transition vitreuse et les propriétés thermomécaniques." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00932853.
Full textAbstract:
Le but de ce travail est de comprendre l'influence des nanoparticules de silice sur les transitions physiques de matrices polymères de nature différente : l'alcool polyfurfurylique (PFA), le polytétrafluoroéthylène (PTFE) et le polydiméthylsiloxane (PDMS). Pour cela, les techniques d'analyse thermique conventionnelles (ATG, DSC, DMA) ont été couplées à des techniques atypiques (DSC multifréquence, FSC, UFSC).Dans le cas du PFA, les nanoparticules de silice ont entrainé une augmentation de la Tg ainsi qu'une amélioration des propriétés thermomécaniques. En outre, il a été démontré que la seule présence de silice suffit à favoriser les mécanismes de polymérisation. La cristallisation du PTFE à partir de l'état fondu a été étudiée pour la première fois sur une gamme de vitesse de refroidissement très large (jusqu'à 800 000 K.s-1). L'effet nucléant des nanoparticules de silice a également été mis en avant à faibles vitesses de refroidissement lors de l'étude de la cristallisation du PTFE chargé. Cependant, il s'est avéré qu'elle ralentit également la diffusion des chaines dans le milieu pour certaines vitesses. L'influence des nanoparticules de silice sur la transition vitreuse et la cristallisation du PDMS a finalement été étudiée. Les résultats ont montré que la silice n'induit pas d'effet significatif sur la transition vitreuse. D'autre part, la silice influence fortement la cinétique de cristallisation. Cet effet a été directement lié au fait que la silice favorise la nucléation sans influencer la diffusion des chaines.
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Leite, Álvaro Joel Moreira. "Advanced nanocomposites based on bioactive glass nanoparticles for biomedical applications." Doctoral thesis, 2019. http://hdl.handle.net/1822/66119.
Full textAbstract:
Tese de Doutoramento em Engenharia Biomédica<br>In biomedicine, there is a need to control the interaction of the biomaterials with the environment at
the nano level. Herein, bioactive nanocomposites based on natural polymers were designed to fulfil the
requirements of advanced tissue engineering. First, natural polymers from different sources were employed:
plant (cashew gum), animal (chondroitin sulphate, hyaluronic acid, and gelatin), and marine-derived (alginate
and chitosan). Moreover, their opportune functionalization by carboxymethylation, oxidation, or
methacrylation, were performed to tailor the final polymer properties and span their applicability. Then,
inorganic phases such as bioactive ions (Ca2+ and PO4
3-) or sol-gel derived bioactive glass nanoparticles
(BGNPs) were strategically conjugated with the polymeric matrices to endow a bioactivity behavior. Besides
the conventional exploited composition of BGNPs based in the ternary system (SiO2-CaO-P2O5), a quaternary
system consisting of doped strontium bioactive glass nanoparticle (Sr-BGNPs, SiO2-CaO-P2O5-SrO) and
hydrophobic bioactive glass nanoparticle (H-BGNPs) were also successfully developed. Despite maintaining
a bioactive performance, these novel nanoparticles improved osteogenic differentiation and allowed confined
bioactive coatings, respectively. The manufacturing of the nanocomposites was achieved through cuttingedge
and innovative micro and nanofabrication technologies: layer-by-layer (LbL); superhydrophobic surfaces
(SHS); liquid marbles; and 3D printing. Crosslinking agents including genipin, irgacure or CaCl2 were also
employed. The acquired know-how allowed the design of multifunctional bioactive systems ranging from ionic
enriched multilayered thin films, shape memory scaffolds, biomaterial high-throughput platforms, hydrogels
with nanostructured shells, and tailor-made hydrogel meshes. These nanocomposite systems were assessed
by standard hi-tech methods: AFM; contact angle; DLS and ζ-potential; DMA; EDX; FTIR; ICP; QCM-D;
rheology; SEM; XPS; XRD; μ-CT; RT-PCR; immunodetection; fluorescent microscopy and immunolabelling.
Moreover, the in-vitro biological performance was evaluated on human umbilical vein endothelial cells
(HUVECs); osteoblastic like cells (SaOs‑2); pre-osteoblast cell line (MC3T3-E1); human osteoblast-like cell
(MG-63); and human adipose stem cells (hASCs). Overall, these bioactive systems possessed increased
osteoconductive properties demonstrated by the establishment of bone-like mineralization in simulated
physiological environments. Moreover, they could smartly store and release therapeutic drug models.
Furthermore, the engineered systems showed superior biocompatibility, sustained cell viability, proliferation,
and early osteogenic commitment of pre‑osteoblastic cell lines and stem cells, potentiating bone cell
therapy. The work herein described could find direct purposes in bone tissue regeneration, but also expands
their applicability in the fields of biotechnology, materials science, and chemistry for applications in sensing,
drug screening, fabrication of 3D microtissues, and biomedicine.<br>Na biomedicina, o controlo da interação dos biomateriais com o meio ambiente à escala
manométrica tornou-se uma necessidade. Assim, nanocompósitos bioativos baseados em polímeros
naturais foram projetados para preencher os requisitos da engenharia de tecidos. Primeiro, utilizou-se
polímeros naturais de diferentes fontes: vegetal (goma de caju), animal (sulfato de condroitina, ácido
hialurônico, e gelatina) e derivados marinhos (alginato e quitosano). Além disso, foi realizada a sua
funcionalização oportuna por carboximetilação, oxidação ou metacrilação para adequar as propriedades
finais do polímero e ampliar seu uso. Posteriormente, fases inorgânicas, como os iões bioativos (Ca2+ e PO4
3-)
ou nanopartículas de vidro bioativas produzidas por sol-gel (BGNPs) foram estrategicamente conjugadas
com as matrizes poliméricas para as dotar de bioatividade. Além da composição convencional de BGNPs
baseados no sistema ternário (SiO2-CaO-P2O5), foi também desenvolvido um sistema quaternário de
nanopartículas de vidro bioativo dopadas com estrôncio (Sr-BGNPs, SiO2-CaO-P2O5-SrO) e nanopartículas de
vidro bioativas hidrofóbicas (H-BGNPs). Além de manter a bioatividade, estas novas nanopartículas
melhoraram a diferenciação osteogênica e permitiram revestimentos bioativos confinados. A produção dos
nanocompósitos realizou-se através de tecnologias inovadoras de micro e nanofabricação: “layer-by-layer”
(LbL); superfícies super-hidrofóbicas (SHS); berlindes líquidos; e impressão 3D. Agentes de reticulação como
a genipina, irgacure ou CaCl2 foram também empregues. Este conhecimento permitiu a concepção de
sistemas bioativos multifuncionais, desde filmes ultrafinos em multicamada enriquecidos com iões, scaffolds
com memória de forma, plataformas de alto rendimento para o rastreio de biomateriais, hidrogéis com
revestimentos nanoestruturados, e malhas de hidrogeis. Os nanocompósitos foram avaliados por métodos
padrão: AFM; ângulo de contato; DLS e potencial-ζ; DMA; EDX; FTIR; ICP; QCM-D; reologia; SEM; XPS; XRD;
μ-CT; RT-PCR; imunodetecção; microscopia de fluorescência e imunomarcação. O desempenho biológico in
vitro foi avaliado em células endoteliais humanas provenientes de veias umbilicais (HUVECs); células
semelhantes a osteoblastos (SaOs-2); linhas celulares pré-osteoblásticas (MC3T3-E1); células humanas
semelhantes a osteoblastos (MG-63); e células estaminais do tecido adiposo (hASCs). Na generalidade,
estes sistemas bioativos demonstraram propriedades osteocondutoras, expressas pelo aparecimento de
mineralização em ambientes fisiológicos simulados. Além disso, os sistemas foram capazes de armazenar
e libertar de forma inteligente modelos de fármacos. Os sistemas projetados mostraram ainda
biocompatibilidade, uma viabilidade celular sustentada, proliferação, e um compromisso osteogênico
precoce, potencializando a terapia de células ósseas. O trabalho aqui descrito encontra desígnios diretos na
regeneração do tecido ósseo, mas também expande a sua aplicação nas áreas de biotecnologia, ciência de
materiais e química para aplicações em triagem de drogas, construção de microtecidos em 3D e
biomedicina.
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Juang, Yih-Chern, and 莊佾宸. "Research on The Pultrusion of Glass Fiber Reinforced Vinyl Ester Nanocomposites." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23423756276289709462.
Full textAbstract:
碩士<br>中國文化大學<br>材料科學與奈米科技研究所<br>96<br>This research presents a proprietary process develop to manufacture pultruded glass fiber reinforced vinyl ester nanocomposites. First, we discussed the synthetic properties and processing probilities of mixing of nano inorganic fillers and vinyl ester（VE）, and dicussed cure kinetics to collocate derive of theory second. Finally, to discuss micro structure, mechanical, physical, thermal and electrical properties of pultruded glass fiber reinforced vinyl ester nanocomposites.
The result of experiment, it was found that 1~3 phr filler contents are suitable for pultrusion. The stabilization of viscosity of wet-out bath was set at 25℃. From gel test and FTIR analysis, VE had good reactive. With DSC analysis, VE had cured at 140℃, and calculused activation of energy Ea was 69kJ/mol, autocatalytic parament m was 0.645 and reactive series n was 1.477 by multiple of Matlab 7.0.1.
In aspect of micro structure of pultruded nanocomposites, it show elements of nano inorganic fillers in composites in XRD, it can observe better wet-out and combination of fiber, resin and nano inorganic fillers in SEM, lower surface roughness in AFM and not only had no inflection of function group C＝C in VE with adding nano inorganic fillers but also disperse in fiber and resin in Raman spectrum indentification.
In aspect of the mechanical properties, there had best flexural strength, flexural modulus, impact strength and hardness with 75.568vol% of glass fiber content and pulling rate at 40cm/min. It was found that 2phr nano Al2O3 contents and 1phr nano mica contents are the best, and 110℃, 3hr for postcure.In aspect of the physical properties, the density of pultruded nanocomposites increased with increasing nano inorganic filler contents, the void content decreased with increasing nano inorganic filler content. In aspect of the thermal properties, the weight loss of pultruded nanocomposites decreased with increasing nano inorganic filler contents, the thermal degraded temperature increased with increasing nano inorganic filler contents. It was found that 3phr nano Al2O3 contents are the best. Its thermal degraded temperature was 460.3℃, increased 11.5%. Therefore, It was found that 2phr nano Al2O3 contents are the best for storage modulus and tan δ, and 110℃, 3hr for postcure. Finally, In aspect of the electrical properties, It was found that 3phr nano Al2O3 contents are the best absorption and shielding effectiveness for electromagnetic absorption and shielding test.
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Liu, Jin-Wei, and 劉晉瑋. "Optimization of novel epoxy/glass fiber nanocomposites utilizing experimental design method." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/64168670942589251619.
Full textAbstract:
碩士<br>國立勤益科技大學<br>化工與材料工程系<br>99<br>In this study, novel nanocomposites are preparation and characterization. The Taguchi experimental design methodology is used to optimize the composition of a nanopowders/glass fiber epoxy resin material comprising nano-alumina, nano-silica, carbon black nanoparticle, epoxy resin, glass fiber and diluent. The effect of nanopowders and diluent addition on the corrosion resistance, thermal properties, and mechanical properties of the various samples are then observed.
The results show that the addition of nanopowders will affect the properties of glass fiber/epoxy composites, resulting in thermal stability, corrosion resistance, glass transition temperature, hardness, storage modulus increased. Overall, that nanocomposite comprising 2 wt.% nano-Al2O3, 2 wt.% nano-SiO2, and 2 wt.% carbon black nanoparticle reduced the thermal expansion coefficient (α1) by 17.55% and increased the thermal decomposition temperature by 5.84% compared to that of the sample with no nanopowders. That nanocomposite comprising 2 wt.% nano-Al2O3, 2 wt.% nano-SiO2, 2 wt.% carbon black nanoparticle , and 3.75 wt.% diluent has the best storage modulus ,water and corrosion resistance.
The experimental data generated in the Taguchi trials are processed using a regression analysis technique in order to derive analytical formulae relating the composition of the composite samples to their mechanical, thermal and corrosion properties. It is shown that the results obtained using the analytical formulae are in good agreement with the experimental observations. Thus, the derived formulae provide a quick and convenient means of predicting the mechanical and thermal response of glass fiber/ epoxy nanocomposites with a known composition without the need for experimental investigation.
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Wu, Ming-Dao, and 吳明道. "Investigating the organoclay effect on mechanical behavior of glass fiber/epoxy nanocomposites." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/01015227588716035369.
Full textAbstract:
碩士<br>國立交通大學<br>機械工程系所<br>94<br>This research is aimed to investigate the organoclay effect on mechanical behaviors of the fiber/epoxy/organoclay nanocomposites. Tensile, flexure and fracture behaviors were considered in this study. To demonstrate the organoclay effect, three different loadings, 2.5, 5 and 7.5 wt% of organoclay were dispersed in the epoxy resin using mechanical mixer followed by sonication. The corresponding glass/epoxy nanocomposites were prepared by impregnating the organoclay epoxy mixture into the dry glass fiber through a vacuum hand lay-up process. For the tensile behaviors, the coupon specimens were tested in MTS machine in both longitudinal and transverse directions. The flexural properties were characterized using three point bending tests. In addition, the fracture behaviors of the fiber composites were determined from the double cantilever beam specimens. From the tensile tests, it was revealed that the longitudinal tensile strength decrease as the organoclay loading increases, on the other hand, the transverse tensile strength as well as the transverse tensile modulus increases with the increase of the organoclay. SEM observation on the transverse failure specimens indicates that the enhanced mechanism is due to the interfacial bonding between the fibers and the surrounding matrix modified by organoclay. The similar tendency was also found in the transverse flexural strength of the composites. From the mode I fracture tests It was indicated that with the increase of the organoclay, the corresponding fracture toughness of the composites decreases appreciably. In addition to the unidirectional lamina, the quasi-isotropic laminates with organoclay were prepared and tested in tension. Experimental results depict that the strength of the laminates is not affected appreciably by the organoclay.
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Bradley, Philip. "Characterisation of the structural properties of ECNF embedded pan nanomat reinforced glass fiber hybrid composites." Thesis, 2016. http://hdl.handle.net/10539/21162.
Full textAbstract:
A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering.
Johannesburg, May 2016<br>In this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications.<br>MT2016
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Srivastava, Sunita. "Structure And Dynamics Of Polymers In Confinement." Thesis, 2009. https://etd.iisc.ac.in/handle/2005/1051.
Full textAbstract:
The thesis describes the study of structure and dynamics of polymers in confined geometry. We study the finite size effect on the dynamics of non glassy and glassy polymers. Systematic measurement have been performed to address the issue of the possibility of entanglement and hence reptation dynamics of the polymer segments in confinement. The confinement effect on the glassy dynamics has been studied for Langmuir monolayers as well as for polymer nanoparticle hybrid systems. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in hybrid systems. The available theories explains the slowing down of the dynamics as the system is cooled from the liquid state in terms of increasing cooperative motion of the molecules. The size of the cooperative region is predicted to grow with reducing temperature. Experiments, theories and simulation in confined dimensions have been motivated to detect this length scale of the cooperatively rearranging region. The surface and interface effects on glass transition were studied using measurements based on modulated differential scanning calorimetry and small angle X ray scattering techniques. The dynamical heterogeneity in glassy polymers were studied using advanced X ray photon correlation spectroscopy techniques. Our studies presented in this thesis are also an small step to contribute to the existing experimental results on studying the surface, interface and finite size effects on the morphology and dynamics of confined systems. These effects were studied for, firstly ultra thin Langmuir monolayers and secondly polymer nanoparticle hybrid systems. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we presents our experimental results on surface morphology and surface dynamics in ultra thin Langmuir monolayer of polymers. Chapter 4 and Chapter 5 discusses the result based on polymer nanoparticle hybrid systems. We provide the summary of our result and the future prospective of the work in Chapter 6. In appendix we have shown the complete derivation of the equation used in Chapter 3 for understanding the surface morphology of Langmuir monoalyers on water surface.
Chapter 1 provides in detail the introduction to several aspects related with the dynamics of both glassy and non glassy polymers in confinement. It starts with brief introduction to structure and dynamics of polymers in bulk. In the next section we discuss the macroscopic viscoelastic behavior of materials followed by a very brief discussion on the common techniques used for such measurement. Further it discusses the theory and several available models present in literature to understand the dynamics of glass transition. This section is followed by discussion on surface and interface effects on structure and dynamics of such systems in confinement. Towards the end of this chapter we discuss the universal behavior of slow dynamic observed in soft glassy materials.
Chapter 2 contains the details of the experimental techniques which has been used for the study. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. The surface morphology and dynamics of Langmuir monolayer of polymers confined at air water interface, under compressive mechanical strain has been discussed in Chapter 3. The results presented for surface morphology are based on the studies using the combination of in situ grazing angle incidence small angle X ray scattering and ex situ atomic force microscopy measurements on monolayers transfered on silicon substrate. The issue of the presence of reptation motion in confinement has been addressed by performing systematic measurements as a function of surface concentration and molecular weight at fixed temperature. The glassy dynamical behavior has been studied on different glassy polymer layer as a function of surface concentration and temperature.
In Chapter 4 we show the glass transition behavior of polymer nanoparticle (PMMA gold) hybrid system based on thermal measurements. This chapter discusses the role of the existence of a length scale in deciding the dynamics of the glass transition temperature of polymers. The confinement effect was tuned by the variation of the inter particle spacing between the nanoparticles in the polymer matrix. It also discusses the model to understand the observed behavior of the glass transition temperature in terms of the tunability of the polymer particle interface and the effect of the interface morphology on the dynamics of glass transition temperature.
Chapter 5 is about the study of dynamics of polymer nanocomposites near glass transition as a function of temperature, wave vector and volume fraction of gold nanoparticles using X ray photon correlation spectroscopy. Based on our experimental results , we provide a phase diagram for dynamics in 2D space of temperature, wave vector and volume fraction for our PMMA gold nanoparticle hybrid samples.
Chapter 6 contains the summary and the future perspective of the work presented.
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Srivastava, Sunita. "Structure And Dynamics Of Polymers In Confinement." Thesis, 2009. http://hdl.handle.net/2005/1051.
Full textAbstract:
The thesis describes the study of structure and dynamics of polymers in confined geometry. We study the finite size effect on the dynamics of non glassy and glassy polymers. Systematic measurement have been performed to address the issue of the possibility of entanglement and hence reptation dynamics of the polymer segments in confinement. The confinement effect on the glassy dynamics has been studied for Langmuir monolayers as well as for polymer nanoparticle hybrid systems. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in hybrid systems. The available theories explains the slowing down of the dynamics as the system is cooled from the liquid state in terms of increasing cooperative motion of the molecules. The size of the cooperative region is predicted to grow with reducing temperature. Experiments, theories and simulation in confined dimensions have been motivated to detect this length scale of the cooperatively rearranging region. The surface and interface effects on glass transition were studied using measurements based on modulated differential scanning calorimetry and small angle X ray scattering techniques. The dynamical heterogeneity in glassy polymers were studied using advanced X ray photon correlation spectroscopy techniques. Our studies presented in this thesis are also an small step to contribute to the existing experimental results on studying the surface, interface and finite size effects on the morphology and dynamics of confined systems. These effects were studied for, firstly ultra thin Langmuir monolayers and secondly polymer nanoparticle hybrid systems. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we presents our experimental results on surface morphology and surface dynamics in ultra thin Langmuir monolayer of polymers. Chapter 4 and Chapter 5 discusses the result based on polymer nanoparticle hybrid systems. We provide the summary of our result and the future prospective of the work in Chapter 6. In appendix we have shown the complete derivation of the equation used in Chapter 3 for understanding the surface morphology of Langmuir monoalyers on water surface.
Chapter 1 provides in detail the introduction to several aspects related with the dynamics of both glassy and non glassy polymers in confinement. It starts with brief introduction to structure and dynamics of polymers in bulk. In the next section we discuss the macroscopic viscoelastic behavior of materials followed by a very brief discussion on the common techniques used for such measurement. Further it discusses the theory and several available models present in literature to understand the dynamics of glass transition. This section is followed by discussion on surface and interface effects on structure and dynamics of such systems in confinement. Towards the end of this chapter we discuss the universal behavior of slow dynamic observed in soft glassy materials.
Chapter 2 contains the details of the experimental techniques which has been used for the study. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. The surface morphology and dynamics of Langmuir monolayer of polymers confined at air water interface, under compressive mechanical strain has been discussed in Chapter 3. The results presented for surface morphology are based on the studies using the combination of in situ grazing angle incidence small angle X ray scattering and ex situ atomic force microscopy measurements on monolayers transfered on silicon substrate. The issue of the presence of reptation motion in confinement has been addressed by performing systematic measurements as a function of surface concentration and molecular weight at fixed temperature. The glassy dynamical behavior has been studied on different glassy polymer layer as a function of surface concentration and temperature.
In Chapter 4 we show the glass transition behavior of polymer nanoparticle (PMMA gold) hybrid system based on thermal measurements. This chapter discusses the role of the existence of a length scale in deciding the dynamics of the glass transition temperature of polymers. The confinement effect was tuned by the variation of the inter particle spacing between the nanoparticles in the polymer matrix. It also discusses the model to understand the observed behavior of the glass transition temperature in terms of the tunability of the polymer particle interface and the effect of the interface morphology on the dynamics of glass transition temperature.
Chapter 5 is about the study of dynamics of polymer nanocomposites near glass transition as a function of temperature, wave vector and volume fraction of gold nanoparticles using X ray photon correlation spectroscopy. Based on our experimental results , we provide a phase diagram for dynamics in 2D space of temperature, wave vector and volume fraction for our PMMA gold nanoparticle hybrid samples.
Chapter 6 contains the summary and the future perspective of the work presented.
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Silva, Henrique Pereira da. "Comportamento mecânico de compósitos de fibra de vidro/epoxy nano-reforçados." Doctoral thesis, 2014. http://hdl.handle.net/10316/28115.
Full textAbstract:
Tese de doutoramento em Engenharia Mecânica, na especialidade de Construção Mecânica, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra<br>Os materiais compósitos laminados de matriz polimérica têm propriedades vantajosas tendo
por isso uma ampla variedade de aplicações. Estes materiais são porém suscetíveis de
sofrerem delaminações que podem debilitar consideravelmente as estruturas. Na direção da
espessura do laminado as fibras não funcionam como um reforço efetivo, pelo que a
resistência entre camadas é sempre menor que a resistência no plano.
Neste trabalho estudam-se compósitos de fibra de vidro do tipo E, costurada sob a
forma de tecido equilibrado tri-direcional e matriz epoxídica modificada com nano-argila
montmorilonita organicamente modificada (OMMT) ou nanotubos de carbono de parede
múltipla (MWCNT). A adição destes nanomateriais pretende melhorar as propriedades
interfaciais e assim contribuir para melhorar o comportamento mecânico destes materiais. No
fabrico dos compósitos trifásicos foi utilizado o processo de moldagem assistida a vácuo a
partir do empilhamento de dez camadas de fibra de vidro previamente impregnadas com
resina nano-modificada.
Para caracterizar e comparar a Tenacidade à Fratura Interlaminar dos compósitos, fibra
de vidro/epóxido foram realizados ensaios de Fratura Interlaminar, com solicitações de carga
em Modo I, Modo II e Modo Misto I/II. De uma forma geral a modificação da matriz com
nanopartículas resultou numa melhoria da Tenacidade à Fratura Interlaminar
independentemente do modo de solicitação. Foi ainda avaliada a influência da nano-argila e
do hidro-envelhecimento na Tenacidade à Fratura Interlaminar e no crescimento de fendas
subcríticas. Os resultados de descoesão subcrítica, apresentados sob a forma de curvas da/dt
versus G, mostraram que o envelhecimento promovido pela água nos compósitos com
nano-argila reduz a Tenacidade à Fratura Interlaminar em Modo I. Por outro lado, a dispersão
da nano-argila na matriz promove uma diminuição significativa da velocidade de crescimento
da fenda subcrítica. Foram ainda observadas as superfícies de Fratura Interlaminar dos
compósitos através de microscopia eletrónica e os mecanismos de ruina foram analisados e
discutidos.
Os efeitos da modificação da matriz com nanopartículas sobre o comportamento à
fadiga dos compósitos, fibra de vidro/epóxido foram avaliados através de ensaios realizados
com cargas cíclicas a amplitude constante, de tração-tração e de flexão em três pontos. A evolução do dano foi controlada pela variação da flexibilidade e variação de temperatura dos
compósitos. Os resultados são apresentados, sob a forma de curvas de gama de tensão versus
o número de ciclos até à rotura (Ds-Nf) e razão de fadiga versus número de ciclos até à rotura
(Ds/sut versus Nf). De um modo geral a adição de nanopartículas à matriz epoxídica resultou
em variações pouco significativas da resistência à fadiga. No entanto a razão de fadiga
aumentou com a presença de nano-argila e nanotubos de carbono de parede múltipla na matriz
epoxídica sugerindo que ambas as nanopartículas podem agir como barreiras à propagação de
fendas por fadiga.
Como complemento foi efetuado um estudo numérico, com recurso ao programa de
elementos finitos MARC-MENTAT 2013. Foram desenvolvidos modelos numéricos usando
elementos de interface coesivos para previsão da delaminação em provetes DCB e MMB de
compósitos de fibra de vidro/epóxido, solicitados em Modo I e Modo Misto I/II,
respetivamente. Para os provetes DCB as previsões numéricas foram comparadas com
resultados experimentais tendo-se observado uma boa concordância em termos de curvas
carga-deslocamento e comprimento de fenda-deslocamento. Quanto aos provetes MMB,
foram identificados dois estágios de propagação da fenda. Numa primeira fase a velocidade
de propagação da fenda é elevada, até se atingir o ponto de aplicação da carga de compressão.
Para além do ponto referido a velocidade de propagação da fenda diminui significativamente.<br>Composite materials with polymeric matrix have advantageous properties having so a great
diversity of applications. These materials are however prone to delamination that can
significantly weaken the structures. In the thickness direction of the laminate, the fibres do not
work as an effective reinforcement, and so that the strength between layers is always lower
than the strength in the plane.
This work studies glass fibre type E composites, sewn in the form of balanced
tri-directional fabric, with epoxy matrix modified with nano-clay organically modified
montmorillonite (OMMT) or multiwalled carbon nanotubes (MWCNT). The inclusion of
these nanomaterials aims to strengthen the interfaces of the laminate and thus contribute to
improve the mechanical behavior of these materials. Vacuum assisted moulding was used in
the manufacture of three-phase composites from the stacking of ten glass fibre layers, preimpregnated
with nano-modified resin.
To characterize and compare the Interlaminar Fracture Toughness of the glass
fibre/epoxy composites, Interlaminar Fracture tests were performed with Mode I, Mode II and
Mixed Mode I/II loadings. In general, the modification of the matrix with nanoparticles
resulted in an improvement of Interlaminar Fracture Toughness regardless of the loading
mode. The influence of the nano-clay and of the ageing in water on Interlaminar Fracture
Toughness and subcritical crack growth was also evaluated. The results of subcritical
debonding, presented in the form of da/dt versus G curves, showed that aging promoted by
water on nano-clay composites reduces the Interlaminar Fracture Toughness in Mode I
loading. On the other hand, dispersion of nano-clay in the matrix promoted a significant
decrease of subcritical crack growth rate. The surfaces of interlaminar fracture were observed
using electron microscopy and the failure mechanisms were analyzed and discussed.
The effects of modifying the matrix with nanoparticles on the fatigue behavior of the
composites were evaluated through constant amplitude tests, for traction-traction and three
point bending loadings. The damage evolution was studied by the analysis of flexibility
variation and temperature variation. The results are presented in the form of stress range
versus number of cycles to failure (Ds-Nf) and fatigue ratio versus number of cycles to failure
(Ds/sut versus Nf). In general, the addition of nanoparticles to the epoxy matrix results in
negligible variations of the fatigue resistance. However, the fatigue ratio increased with the presence of nano-clay and carbon nanotubes in the epoxy matrix, suggesting that both
nanoparticles can act as barriers to the propagation of fatigue cracks.
A numerical study was developed to complement the experimental analysis using the
finite element program MARC-Mentat 2013. Numerical models were developed using
cohesive interface elements for predicting delamination in DCB and MMB specimens of
composite glass fibre/epoxy, loaded in Mode I and Mixed Mode I/II, respectively. The
predictions obtained for the DCB specimens were compared with experimental results and a
good agreement was observed in terms of load-displacement and crack length-displacement
curves. In the MMB specimens two stages of crack propagation were identified. Initially, the
rate of crack propagation is relatively high, decreasing significantly beyond the point of
application of the compressive load.<br>FCT - Projeto nº PTDC/EME-PME/113695/2009
32
Maharana, Aditya Narayan. "Synthesis and Characterization of Glass Particulate – Epoxy Composite for Structural Application." Thesis, 2015. http://ethesis.nitrkl.ac.in/7323/1/Synthesis_Maharana_2015.pdf.
Full textAbstract:
The objective of this present project work is to prepare and study of the mechanical properties of glass particulate- epoxy composites. A vast amount of research was carried out involving different morphologies of the glass particulates, for e.g. spherical, flakes, rounded etc., for synthesizing epoxy-glass composites. But in this thesis, crushed laboratory waste glasses with acicular morphology were used as a reinforcement to prepare polymer matrix composite material. Five different compositions of the glass particulate, viz., 0, 5, 10, 15 and 20 vol% have been used in the present work. Detailed characterizations like density measurement, X-ray analysis was done for these composite materials, subsequently these polymer matrix composites with different content of glass particulate were subjected to various types of mechanical testing. It was found that tensile properties were increasing from 0 to 5 vol% of reinforcement content, after that a decreasing trend was observed. But other properties like flexural, impact, compression properties were decreasing as compared to the epoxy resin. This work also described about the comparison of the mechanical properties of composites before and after post curing, carried out at 100oC for 15 minutes.
33
Kumar, Dhirendra. "Study of Deformation and Erosion Behaviour of Epoxy-Glass Microballoon Based Syntactic Foam." Thesis, 2015. http://ethesis.nitrkl.ac.in/7143/1/Study_KumarD_2015.pdf.
Full textAbstract:
The present work is focused on the synthesis and study of the deformation behavior of epoxy resin/glass microballoonbased syntactic foams. Different densities syntactic foams with 0 to 40 volume percentages of glass microballoons were prepared by stir-casting method for the present investigation. The high viscosities of the resin-microballoons mixture (putty like consistency) beyond 40 volume percentage prevents processing of higher microballoon content syntactic foam. The effect of glass microballoon content on tensile, compression, flexural and impact properties were studied in detailes. The results show that specific tensile strengths of the foam was increased by about 34% along with the reduction in density (by about 38%), starting from pure resin to foams with 40% glass microballoon. It is also found that compressive strength of the foam decreases from 140 MPa (for pure resin) to 75 MPa (with 40 vol.% reinforcement). During tensile loading, deformation occurs predominantly through shear yielding of the resin matrix followed by debonding at the matrix-microballoon interface. The crushing of the glass microballoons and subsequent densification of the foams is responsible for large amount of plastic strain during compressive deformation. The erosion behavior of the syntactic foam is also investigated as a function of the different glass microballoons content. Three different erodent velocities (48, 70, 82 m sec-1) and three different angles of impingement (30o, 60o and 90o) are used as experimental parameters in the present investigation. The erosion rate is found to be highest for 40 vol.%reinforcementas compared to pure resin due to presence of larger amount of hollow glass microspheres.
34
Thomas, Ashley George. "Polymer and Glass-Ceramics Composite Scaffolds for Bone Tissue Engineering." Thesis, 2021. http://ethesis.nitrkl.ac.in/10282/1/2021_PhD_AGThomas_512CR1012_Polymer.pdf.
Full textAbstract:
The use of conventional bone repair techniques involving bone grafts has limited potential because of the likelihood of disease transmission and because of their limited supply. Bone tissue engineering is a potential alternative to overcome these limitations, which enables implant scaffolds to stimulate tissue formation directly in-vivo. It is a technique aimed at induced bone regeneration by combining different biomaterials and other functional materials. Arrays of biomaterials have been used in bone tissue engineering due to their attractive properties, such as osteo-conductivity and biocompatibility. The widely used materials include biodegradable polymers and ceramics such as hydroxyapatite, bioactive glasses and glass ceramics.
Natural polymers like alginate, gelatin and chitosan are attractive biomaterials because of their close resemblance with extra-cellular matrix components, thus making them highly biocompatible. However, these polymers suffer from poor bioactivity and low strength. Making a composite scaffold using the bioactive glass-ceramics and polymer can improve the toughness and mechanical stability of the scaffold while maintaining good bioactivity and biocompatibility.
The glass-ceramics (GC) in the system P2O5-Na2O-CaO-SiO2 was synthesized using sol gel technique. The GC showed to contain combeite crystalline phase which is important for bioactivity and bio-dissolution of the GC. The GC showed good bioactivity and biocompatibility. The GC powder was used in the fabrication of composite scaffold. Two types of scaffolds were fabricated where GC was used; (a) as filler in a polymer (chitosan, alginate and gelatin) matrix scaffolds prepared by freeze drying method, and (b) as a ceramic skeleton in the sponge replicated GC scaffolds those coated with three different polymers.
The composite scaffolds prepared by freeze drying showed highly macroporous (~80%) structures with good pore connectivity which is ideal for bone tissue engineering application. In general, composite scaffolds showed the improvement of different properties such as mechanical strength, bioactivity, cell adhesion, alkaline phosphatase activity and osteogenicity with increase in GC powder loading in polymer matrix of the scaffold. Among all, gelatin based scaffolds showed highest compressive strength exhibiting 5.8 MPa in the scaffold containing 5 wt% GC. Gelatin based scaffolds also showed excellent cell adhesion and proliferation compared to the other. Alginate-chitosan-GC based scaffolds showed improved strength compared to chitosan-GC based scaffolds and better cell proliferation compared to alginate-GC scaffolds.
Sponge replication was used to prepare GC scaffolds doped with 6 wt% titania through sintering of GC. The strength of the porous GC scaffold was improved by doping with titania which acts as a sintering additive. The strength of the scaffolds was further improved by coating with alginate, gelatin and chitosan. Among all, gelatin coated GC scaffolds showed highest compressive strength and relatively better cell adhesion properties. Microtomography was used for in-detail examination of pore characteristics in scaffolds. The scaffolds exhibited highly porous architecture with open pores. A clear understanding of pore size distribution was obtained. The scaffolds showed macoporous structure ideal for bone tissue engineering. The pore sphericity, orientation and interconnectivity were analyzed in details. The results demonstrated that the composite scaffolds are potential candidates for bone tissue engineering.
35
Putz, Karl William Green Peter F. "The dynamic mechanical response of polymer-based nanocomposites and network glasses." 2004. http://repositories.lib.utexas.edu/bitstream/handle/2152/2168/putzkw042.pdf.
Full text
36
Putz, Karl William. "The dynamic mechanical response of polymer-based nanocomposites and network glasses." Thesis, 2004. http://hdl.handle.net/2152/2168.
Full text
37
Olusanya, John Olumide. "Fatigue performance of nanoclay filled glass fiber reinforced hybrid composite laminate." Thesis, 2017. http://hdl.handle.net/10321/2464.
Full textAbstract:
Submitted in fulfilment of the requirements for the degree of Master of Engineering: Mechanical Engineering, Department of Mechanical Engineering, Faculty of Engineering and the Built Environment, Durban University of Technology, Durban, South Africa. 2017.<br>In this study, the fatigue life of fiber reinforced composite (FRC) materials system was investigated. A nano-filler was used to increase the service life of the composite structures under cyclical loading since such structures require improved structural integrity and longer service life. Behaviour of glass fiber reinforced composite (GFRC) enhanced with various weight percentages (1 to 5 wt. %) of Cloisite 30B montmorillonite (MMT) clay was studied under static and fatigue loading.
Epoxy clay nanocomposite (ECN) and hybrid nanoclay/GFRC laminates were characterised using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The mechanical properties of neat GFRC and hybrid nanoclay/GFRC laminates were evaluated. Fatigue study of the composite laminates was conducted and presented using the following parameter; matrix crack initiation and propagation, interfacial debonding, delamination and S–N relationship. Residual strength of the materials was evaluated using DMA to determine the reliability of the hybrid nanoclay/GFRC laminates.
The results showed that ECN and hybrid nanoclay/GFRC laminates exhibited substantial improvement in most tests when compared to composite without nanoclay. The toughening mechanism of the nanoclay in the GFRC up to 3 wt. % gave 17%, 24% and 56% improvement in tensile, flexural and impact properties respectively. In the fatigue performance, less crack propagations was found in the hybrid nanoclay/GFRC laminates. Fatigue life of hybrid nanoclay/GFRC laminate was increased by 625% at the nanoclay addition up to 3 wt. % when compared to neat GFRC laminate. The residual strength of the composite materials revealed that hybrid nanoclay/GFRC showed less storage modulus reduction after fatigue. Likewise, a positive shift toward the right was found in the tan delta glass transition temperature (Tg) of 3 wt. % nanoclay/GFRC laminate after fatigue. It was concluded that the application of nanoclay in the GFRC improved the performance of the material. The hybrid nanoclay/GFRC material can therefore be recommended mechanically and thermally for longer usage in structural application.<br>M
38
Chandran, Sivasurender. "Structure and Dynamics of Binary Mixtures of Soft Nanocolloids and Polymers." Thesis, 2013. https://etd.iisc.ac.in/handle/2005/3458.
Full textAbstract:
Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5).
In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively.
In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight.
In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.
39
Chandran, Sivasurender. "Structure and Dynamics of Binary Mixtures of Soft Nanocolloids and Polymers." Thesis, 2013. http://etd.iisc.ernet.in/2005/3458.
Full textAbstract:
Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5).
In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively.
In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight.
In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.