Academic literature on the topic 'Sol-gel phase transition'
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Journal articles on the topic "Sol-gel phase transition"
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Bilge, Ayse Humeyra, Arif Selcuk Ogrenci, and Onder Pekcan. "Mathematical models for phase transitions in biogels." Modern Physics Letters B 33, no. 09 (March 30, 2019): 1950111. http://dx.doi.org/10.1142/s0217984919501112.
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It has been shown that reversible and irreversible phase transitions of biogels can be represented by epidemic models. The irreversible chemical sol–gel transitions are modeled by the Susceptible-Exposed-Infected-Removed (SEIR) or Susceptible-Infected-Removed (SIR) epidemic systems whereas reversible physical gels are modeled by a modification of the Susceptible-Infected-Susceptible (SIS) system. Measured sol–gel and gel–sol transition data have been fitted to the solutions of the epidemic models, either by solving the differential equations directly (SIR and SEIR models) or by nonlinear regression (SIS model). The gel point is represented as the “critical point of sigmoid,” defined as the limit point of the locations of the extreme values of its derivatives. Then, the parameters of the sigmoidal curve representing the gelation process are used to predict the gel point and its relative position with respect to the transition point, that is, the maximum of the first derivative with respect to time. For chemical gels, the gel point is always located before the maximum of the first derivative and moves backward in time as the strength of the activation increases. For physical gels, the critical point for the sol–gel transition occurs before the maximum of the first derivative with respect to time, that is, it is located at the right of this maximum with respect to temperature. For gel–sol transitions, the critical point is close to the transition point; the critical point occurs after the maximum of the first derivative for low concentrations whereas the critical point occurs after the maximum of the first derivative for higher concentrations.
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dos Santos, L. R. B., A. F. Craievich, C. V. Santilli, and S. H. Pulcinelli. "Sol phase and sol–gel transition in SnO2colloidal suspensions." Journal of Applied Crystallography 33, no. 3 (June 1, 2000): 609–13. http://dx.doi.org/10.1107/s0021889899012686.
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Sharma, H. BASANTAKUMAR, and Abhai Mansingh. "Phase transition in Sol-Gel processed barium titanate ceramics." Ferroelectrics Letters Section 23, no. 1-2 (August 1997): 37–43. http://dx.doi.org/10.1080/07315179708203404.
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Yan, Zhi-Chao, Chandra Sekhar Biswas, and Florian J. Stadler. "Rheological Study on the Thermoreversible Gelation of Stereo-Controlled Poly(N-Isopropylacrylamide) in an Imidazolium Ionic Liquid." Polymers 11, no. 5 (May 2, 2019): 783. http://dx.doi.org/10.3390/polym11050783.
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The thermoreversible sol-gel transition for an ionic liquid (IL) solution of isotactic-rich poly (N-isopropylacrylamides) (PNIPAMs) is investigated by rheological technique. The meso-diad content of PNIPAMs ranges between 47% and 79%, and molecular weight (Mn) is ~35,000 and ~70,000 g/mol for two series of samples. PNIPAMs are soluble in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([BMIM][TFSI]) at high temperatures but undergo a gelation with decreasing temperatures. The transition temperature determined from G’-G” crossover increases with isotacticity, consistent with the previous cloud-point result at the same scanning rate, indicating imide groups along the same side of backbones are prone to be aggregated for formation of a gel. The transition point based on Winter-Chambon criterion is on average higher than that of the G’-G” crossover method and is insensitive to tacticity and molecular weight, since it correlates with percolation of globules rather than the further formation of elastic network (G’ > G”). For the first time, the phase diagram composed of both G’-G” crossover points for gelation and cloud points is established in PNIPAM/IL mixtures. For low-Mn PNIPAMs, the crossover-point line intersects the cloud-point line. Hence, from solution to opaque gel, the sample will experience two different transitional phases, either clear gel or opaque sol. A clear gel is formed due to partial phase separation of isotactic segments that could act as junctions of network. However, when the partial phase separation is not faster than the formation of globules, an opaque sol will be formed. For high-Mn PNIPAMs, crossover points are below cloud points at all concentrations, so their gelation only follows the opaque sol route. Such phase diagram is attributed to the poorer solubility of high-Mn polymers for entropic reasons. The phase diagram composed of Winter-Chambon melting points, crossover points for melting, and clear points is similar with the gelation phase diagram, confirming the mechanism above.
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Turchetto, Alessandro, and Attilio Cesàro. "Gel-sol phase transition of poly(3-hydroxybutyrate) in dimethylformamide." Thermochimica Acta 269-270 (December 1995): 307–17. http://dx.doi.org/10.1016/0040-6031(95)02572-3.
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Sharma, H. Basantakumar, and Abhai Mansingh. "Phase transition in sol-gel-derived barium titanate thin films." Journal of Physics D: Applied Physics 31, no. 13 (July 7, 1998): 1527–33. http://dx.doi.org/10.1088/0022-3727/31/13/006.
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Shannigrahi, Santiranjan, R. N. P. Choudhary, H. N. Acharya, and T. P. Sinha. "Phase transition in sol-gel-derived Na-modified PLZT ceramics." Journal of Physics D: Applied Physics 32, no. 13 (January 1, 1999): 1539–47. http://dx.doi.org/10.1088/0022-3727/32/13/315.
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Gatelyte, Aurelija, Darius Jasaitis, Aldona Beganskiene, and Aivaras Kareiva. "Sol-Gel Derived Ferrites: Synthesis and Characterization." Advanced Materials Research 222 (April 2011): 235–38. http://dx.doi.org/10.4028/www.scientific.net/amr.222.235.
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In the present work, the sinterability and formation of nanosized yttrium iron garnet (Y3Fe5O12), yttrium perovskite ferrite (YFeO3), cobalt, nickel and zinc iron spinel (CoFe2O4, NiFe2O4 and ZnFe2O4, respectively) powders by an aqueous sol-gel processes are investigated. The phase purity of synthesized nano-compounds was characterized by powder X-ray diffraction analysis (XRD). The microstructural evolution and morphological features of obtained transition metal ferrites were studied by scanning electron microscopy (SEM). The possible application of these nanosized transition metal ferrites as ceramic pigments was demonstrated.
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Xu, Dong Ying, Zheng Fu Liao, and Hui Wang. "Sol-Gel Transition Kinetics of Konjac Glucomannan Dilute Solution by Fluorescence Technique." Advanced Materials Research 399-401 (November 2011): 1326–29. http://dx.doi.org/10.4028/www.scientific.net/amr.399-401.1326.
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Konjac glucomannan (KGM) has been widely used in pharmaceutical, chemical engineering, food industry, drug carrier delivery, etc. The sol-gel transition kinetics of KGM dilute solution was studied by steady fluorescence spectroscopy in this article. The results showed that the gel point of KGM solutions depend on the concentration of KGM, pH value and temperature. The sol-gel phase transition activation energy, ΔE, was calculated to be 83.1 kJ/mol based on first reaction kinetic model.
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Yu, Xia, Hui Chen, Xiang Shi, Pierre-Antoine Albouy, Jia Guo, Jun Hu, and Min-Hui Li. "Liquid crystal gelators with photo-responsive and AIE properties." Materials Chemistry Frontiers 2, no. 12 (2018): 2245–53. http://dx.doi.org/10.1039/c8qm00340h.
Full textDissertations / Theses on the topic "Sol-gel phase transition"
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Gasparoux, Jennifer. "Etude rhéo-acoustique de gels polymères polydiméthylsiloxanes." Montpellier 2, 2007. http://www.theses.fr/2007MON20037.
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Stegall, Stacy L. "Separation of Transition and Heavy Metals Using Stationary Phase Gradients and Chelation Thin Layer Chromatography / Evaluation of the Effectiveness of POGIL-PCL Workshops." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4779.
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Gradient surfaces exhibit a variation in functionality along the length of the surface. One method for preparing gradients is controlled-rate infusion (CRI). In Part 1 of this work, CRI was used to prepare gradients for the purpose of separating transition and heavy metals. Initial work on this project was focused on controlling the retention of the metal ions by varying the number of amine groups, aminoalkoxysilane concentration, and the infusion time. The retention factors of four metal ions varied predictably with increasing number of amine groups, increasing aminoalkoxysilane concentration, and increasing infusion time, producing small but useful changes in the retention factors. The continuation of this project involved the preparation of two-dimensional multi-component gradients on TLC plates, which were used to separate six transition and heavy metals. The retention, and thus the separation, was affected by the presence or absence of a gradient and the direction of the gradient.
Part 2 of this work focused on understanding the factors that motivated instructors in the early and late stages in the process of change. Instructors who attended the POGIL-PCL (Process-Oriented Guided Inquiry Learning in the Physical Chemistry Laboratory) workshops were asked to complete online surveys. The goals of the first survey were to understand the factors that initially interested instructors in POGIL-PCL, to determine if instructors enter the implementation stage, and to understand the factors that affect how instructors implement POGIL-PCL. Later surveys were designed to explore the development of the POGIL-PCL network and assess whether implementation is sustained over time.
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Ould, Ehssein Chighali. "Système instrumental pour la rhéologie ultrasonore." Cergy-Pontoise, 2006. http://biblioweb.u-cergy.fr/theses/06CERG0309.pdf.
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L'élaboration de fluides complexes (les produits de soins, ménagers ou agroalimentaires), constitue un enjeu économique important. En particulier, la mise au point de nouveaux matériaux à transition de phase s'avère en fait très complexe. Elle nécessite un suivi précis des caractéristiques viscoélastiques à l'aide de systèmes de contrôle non destructifs adaptés. Le dispositif expérimental original développé dans le cadre de cette thèse utilise un capteur piézoélectrique qui a été dimensionné de sorte à optimiser sa sensibilité. Pour extraire les caractéristiques du matériau, un nouveau modèle électrique a été développé. Il tient compte simultanément des évolutions électriques et mécaniques du matériau. Nous validons notre instrumentation et le modèle associé sur deux types matériaux : des matériaux élaborés par le procédé sol-gel (peu conducteurs) et des yaourts en formation (conducteurs)The development of complex fluids for care, domestic or agroalimentary products constitutes an important economic stake. The development of new materials with phase transition is in fact very complex. It requires an accurate follow-up of the viscoelastic characteristics by using a non destructive testing method. The present work describes an adapted electronic set-up. The experimental set-up is based on a piezoelectric quartz crystal resonator in contact with the material. The quartz electrical impedance is used to monitor and to extract the complex shear modulus of the material. A new electrical model of the loaded quartz is developed and validated with well-known viscous conductive fluids. This new experimental set-up is successfully applied to the gelation process monitoring of two typical materials. The first one is a silica gel, the second one is a dairy product made from acidified milk
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Boháčová, Zdeňka. "Polymerace za otevření kruhu laktonů a laktidů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2015. http://www.nusl.cz/ntk/nusl-233379.
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Medicínské aplikace tvoří z biodegradabilních alifatických polyesterů na bázi polylaktonů, polylaktidů a jejich kopolymerů velmi atraktivní skupinu materiálů. Metody přípravy těchto polymerů jsou založeny na polymeraci za otevření kruhu laktonů a laktidů. Mnoho organokovových sloučenin se vyznačují jako účinné a vysoce selektivní katalyzátory těchto polymerací, avšak je známo, že deriváty těžkých kovů jsou škodlivé pro lidský organismus. Z tohoto důvodu je v dnešní době rostoucí zájem o vývoj účinných „green“ polymeračních systémů pro syntézu biodegradabilních alifatických polyesterů. Předložená disertační práce se věnuje přípravě alifatických polyesterů založených na polykaprolaktonu, polylaktidu, polyglykolidu a zejména jejich kopolymeru pomocí organického katalyzátoru náležícího do skupiny N-heterocyklických karbenů (NHC) bez přítomnosti centrálního atomu těžkého kovu. Literární rešerše je zaměřená na pokroky v polymeraci za otevření kruhu (ROP) cyklických esterů (laktonů a laktidů) pomocí organických "metal-free" katalyzátorů. Nicméně, nebyly nalezeny žádné studie, kde se pro přípravu polyglykolidu nebo jeho kopolymerů využívá polymerace za otevření kruhu pomocí karbenových katalyzátorů. Experimentální část práce popisuje přípravu a vlastnosti 1,3-di-tert-butylimidazol-2-ylidenu (NHC-tBu) karbenu připraveného z jeho stabilní chloridové soli. Další část je zaměřena na přípravu polyesterů z cyklických monomerů, jmenovitě L-laktidu, D, L-laktidu, glykolidu a -kaprolaktonu pomocí NHC-tBu jako katalyzátoru. Byla zkoumána nová metoda přípravy termosenzitivního amfifilního triblokového kopolymeru na bázi biodegradabilního hydrofobního polylaktidu, polyglykolidu a biokompatibilního hydrofilního polyethylenglykolu (PLGA–PEG–PLGA) pomocí připraveného NHC-tBu. Dále byly studovány podmínky polymerace (například: přečištění monomeru, teploty polymerace, různé typy rozpouštědel, poměry rozpouštědla ku monomeru a nebo různé poměry iniciátoru ku katalyzátoru). Na závěr byl připravený PLGA–PEG–PLGA kopolymer srovnán s kopolymerem připraveným pomocí Sn(II)2-ethylhexanoátu. NHC-tBu se v přítomnosti PEG projevil jako účinný katalyzátor polymerace za otevření kruhu laktonu a laktidů. Připravené kopolymery dosahovaly vysoké konverze monomeru (70 – 85%) s polydisperzitou (Mw/Mn okolo 1,2). Byl připraven PLGA–PEG–PLGA kopolymer se dvěma fázovými přechody (sol-gel a gel suspenze) a gelační teplotou v rozmezí 35 – 43 °C. Změny polymeračních podmínek neměly ve většině případů zásadní vliv na chemické vlastnosti kopolymeru, jako jsou molekulová hmotnost nebo polydisperzita, ale měly významný vliv na visko-elastické vlastnosti.
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Michlovská, Lenka. "Syntéza a charakterizace multifunkcionalizovaných biodegradabilních kopolymerů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2014. http://www.nusl.cz/ntk/nusl-233392.
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Předložená disertační práce shrnuje současné poznatky v oblasti termosenzitivních biodegradabilních kopolymerů, které ve formě vodného solu gelují při teplotě lidského těla. Tyto polymerní materiály jsou použitelné v medicíně pro injekční aplikace jako nosiče léčiv či resorbovatelné implantáty pro regeneraci tkání. V experimentální práci byly pomocí vakuové linky syntetizovány termosenzitivní amfifilní triblokové kopolymery na bázi biodegradabilního hydrofobního polylaktidu a polyglykolidu a biokompatibilního hydrofilního polyethylenglykolu (PLGA–PEG–PLGA). Připravený PLGA–PEG–PLGA kopolymer se dvěma fázovými přechody sol-gel a gel-suspenze byl následně modifikován anhydridem kyseliny itakonové. Výsledný funkcionalizovaný ITA/PLGA–PEG–PLGA/ITA kopolymer obsahuje na koncích řetězců reaktivní dvojné vazby vhodné k další polymeraci či síťování a karboxylové skupiny pro případné modifikace biologicky aktivními látkami. Fyzikální i chemické síťování bylo dále sledováno jak z hlediska poměrů hydrofilního a hydrofobního řetězce, tak i z hlediska množství navázané kyseliny itakonové. Vodné roztoky syntetizovaného ITA/PLGA–PEG–PLGA/ITA kopolymeru gelují v rozmezí teplot 33 - 43 °C. Kritická gelační koncentrace byla 6 % a kritická gelační teplota 34 °C pro kopolymer s poměrem PLGA/PEG = 2,5. Čím je kopolymer více hydrofobní, tím geluje dříve a je více hydrolyticky stabilní. Tuhost gelu stoupá se zvyšujícím se poměrem PLGA/PEG a je závislá na typu rozpouštědla použitého při přečišťování kopolymeru. Připravené ITA/PLGA–PEG–PLGA/ITA makomonomerů byly síťovány pomocí modrého světla bez dalšího síťovadla. Hydrolytická stabilita vzorků modifikovaných pomocí ITA se výrazně zlepšila a zvýšila v přímé úměře jak s rostoucí dobou síťování, tak s množstvím dvojných vazeb na koncích řetězců. Vzorek s 63 mol% ITA síťovaný 40 minut ve vodě zcela zdegradoval po 32 dnech. Protonovou NMR relaxometrií bylo zjištěno, že když vzorek ve vodě nabotnal (po cca 12 hodinách), množství nevázané vody se začalo snižovat a postupně difundovat do kavit na povrchu vzorku a pomalu se měnit na slabě a pevně vázanou vodu na polymerní řetězce. Nicméně, termální stabilita chemicky síťovaných vzorků vzrůstala pouze do 20 minut síťování. Pomocí ATR-FTIR bylo prokázáno, že se přibližně 57 % dvojných vazeb kyseliny itakonové (při vlnové délce 1640 cm-1) přeměnilo na nové jednoduché RR'C-CHR'' vazby při vlnové délce 795 cm-1. Delší čas síťování (nad 30 minut) vedl ke změnám v chemické struktuře pomocí beta-štěpení řetězců a částečné rekombinaci dvojných vazeb. Díky vzniku nových dvojných vazeb v jiných částech řetězce se snížila termální stabilita z 242 °C na 237° C a teplota skelného přechodu z -2,2 na -5.8 °C. Předložená práce popisuje, jak složení polymeru, modifikace funkčními skupinami a fyzikální podmínky ovlivňují fyzikální a chemické síťování připravených amfifilních kopolymerů. Kontrola hydrolytické a termální stability hydrogelů je zapotřebí zejména při uvolňování léčiv a regeneraci tkání.
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Fischer, Hannes. "Estudos estruturais de xerogéis de óxido de níquel." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-09102001-185623/.
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Foram estudadas as características estruturais de xerogéis obtidos pelo método sol-gel a partir de soluções líquidas precursoras compostas de cloreto de níquel (NiCl2), butanol, água e ácido acético, secos em estufa e tratados a diferentes temperaturas entre 150 e 900ºC. Nos tratamentos isotérmicos a essas temperaturas os elementos voláteis se desprendem do material inicial e transformações estruturais acontecem. Analisaram-se os materiais porosos resultantes (xerogéis) mediante técnicas estruturais: espalhamento de raios X a baixo ângulo (SAXS), espectroscopia de absorção de raios X (XANES e XAFS), difração de raios X (XRD) e microscopia eletrônica de varredura. Complementaram-se estes estudos mediante análise química (espectroscopia de infravermelho), térmica (análise térmica diferencial), gravimétrica (perda de massa) e de densidade. Os resultados experimentais demonstraram que a estrutura porosa do material inicial à base de NiCl2 se transforma numa estrutura bifásica, também porosa, composta por uma fase rica em NiCl2 e outra em óxido de níquel (NiO), sendo que a fração de volume ocupada pela fase de NiO no material final aumenta com a temperatura de tratamento térmico. No caso de temperaturas acima de 500ºC, praticamente todo o volume da amostra se transforma e é ocupado pela fase NiO. Mostrou-se que a estrutura porosa presente em todos os materiais, estudada por SAXS, é composta por nanoporos (10-150Å) e mesoporos (maiores que 150Å), sendo que a fração de volume ocupada pelos mesmos depende da temperatura do tratamento térmico. Em particular os nanoporos somente estão presentes nas amostras tratadas abaixo de 500ºC. A ordem local média ao redor dos átomos de Ni, determinada por EXAFS, corresponde ao esperado de sistemas bifásicos cujas frações de volume dependem da temperatura de tratamento, em concordância com os resultados de XRD. Investigaram-se as características dos materiais obtidos após os diferentes tratamentos térmicos em função de diferentes condições de preparação das soluções precursoras. Numa primeira série de experiências, variou-se o conteúdo de ácido acético na solução. Demonstrou-se que maiores concentrações de ácido acético promovem a formação de um material com estrutura mais compacta. Numa segunda série de experiências variou-se o conteúdo de água. Determinou-se que a quantidade de água afeta somente a estrutura dos materiais tratados a temperaturas inferiores à 500ºC.Structural properties of several xerogels obtained by the sol-gel procedure and heat treated at different temperatures between 150 and 900ºC were studied. The initial systems were dry gels prepared from liquid solutions composed of nickel chloride, buthanol, water and acetic acid. During the different isothermal treatments, volatile species leave the inicial material and structural transformations occur. The resulting porous materials (xerogels) were studied by means of several structural techniques: small angle X ray scattering (SAXS), X ray absorption spectroscopy (XANES and EXAFS), X ray diffraction (XRD) and scanning electron microscopy. These studies were complemented with chemical analysis (infrared spectroscopy), differential thermal analisis, mass loss and density measurements. The experimental results demonstrated that the porous structure of the starting material, based on nickel chloride, transforms in a also porous biphasic structure composed of nickel chloride and nickel oxide, respectively, rich fase. The volume fraction occupied by the nickel oxide rich fase of the final material increases with temperature of heat treatment. For temperatures above 500ºC, practically all the sample volume transforms and is occupied by the NiO phase. It was demonstrated that the porous structure of all materials, studied by SAXS, is composed of nanopores (sizes ranging from 10 to 150Å ) and mesopores (larger than 150Å), their fraction depending on the heat treatment temperature. Particularly, nanopores are only present in samples treated below 500ºC. The average local order close to nickel atoms, determined by EXAFS, corresponds to the expected one for biphasic systems whose volume fractions depend on treatment temperature, in agreement with XRD results. The structural properties of the several materials obtained after different heat treatments were studied as functions of preparation conditions of precursor solutions. In a first series of experiments, acetic acid content in the solution was varied. It was demonstrated that higher acetic acid content promotes the formation of more compact structures. In a second series of experiments, water content was varied. It was concluded that water content only affects the structure of the materials heat treated at temperatures below 500ºC.
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Lapp, Alain. "Synthese, conformation et interactions de molecules lineaires et ramifiees de polydimethylsiloxane : mise en evidence de lois d'universalite." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13108.
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Synthese du polydimethylsiloxane etudie et etude de l'hydrosilation se produisant au cours de la reticulation en solution semidiluee, relation entre la longueur de correlation et la concentration. Interactions a trois corps dans le styrene, solvant theta du pdmsi
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Legrand-Buscema, Caroline. "Préparation de SrBi2Nb2O9 par voie sol-gel : cristallisation des poudres et couches minces épitaxiées." Limoges, 2000. http://www.theses.fr/2000LIMO0034.
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La tendance generale a la miniaturisation des dispositifs conduit de plus en plus a focaliser les recherches sur les materiaux fonctionnels en couches minces. Parmi ces materiaux, les ferroelectriques prennent une place de plus en plus importante notamment dans le domaine des memoires non volatiles. Si les pzt ont deja fait l'objet de nombreux travaux, les recherches sur les composes ferroelectriques a couches de bismuth ou phases d'aurivillius sont en plein essor en raison de leur resistance a la fatigue et de leur aptitude a conserver leur polarisation apres de nombreux cycles de fonctionnement. Dans le cadre general, et compte tenu de l'experience acquise au spcts dans ce domaine, le travail presente concerne une des phases d'aurivillius parmi les plus prometteuses, srbi 2nb 2o 9 (sbn), pour laquelle persistent encore des zones d'ombre concernant a la fois la fabrication, la nature des defauts structuraux, son epitaxie sur divers substrats monocristallins, ce dernier point etant etroitement lie a son utilisation dans les memoires (possibilite d'obtenir des couches ferroelectriques avec des orientations choisies de la polarisation par rapport au substrat). Sbn a ete prepare par voie sol-gel selon une technique deja utilisee au spcts. La cristallisation des xerogels, puis son orientation et l'epitaxie de couches deposees par centrifugation (spin-coating) ont ete etudiees a la fois par diffraction des rayons x et par microscopie electronique en transmission. La fabrication de la phase sbn cristallisee passe toujours par la formation d'une phase intermediaire de type fluorine de composition inconnue, certainement riche en bismuth, qui pourrait etre le precurseur des feuillets bi 2o 2 caracteristiques des phases d'aurivillius
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Silva, Maria Claudia. "Influence de l'organisation nanostructurale des précurseurs de zircone sur les processus de cristallisation et de transformation de phase." Limoges, 1996. http://www.theses.fr/1996LIMO0059.
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Ce travail concerne l'etude de nanopoudres de zircone obtenues par voie sol-gel dans systeme n-propoxyde de zirconium/n-propanol/acetylacetone/eau. Cette etude vise a preciser l'influence de l'organisation spatiale des particules elementaires presentes au sein des precurseurs sur les mecanismes de cristallisation et de transformation de phase se produisant ulterieurement lors de recuits. Dans cette optique, differents produits ont ete synthetises. En l'absence d'agent complexant, la formation de precipite est mise en evidence. Dans le cas contraire, un gel transparent est obtenu. Selon le type de sechage envisage pour le gel, deux autres produits sont alors elabores. Un sechage conventionnel en etuve permet d'obtenir un xerogel, tandis qu'un sechage en condition hypercritique en autoclave aboutit a la formation d'un aerogel. L'etude de l'organisation nanostructurale des precurseurs des trois produits en diffusion centrale de rayons x (dcrx) montre que ces produits different fortement. La cristallisation de ces differents precurseurs est etudiee ensuite. Les mecanismes de cristallisation mis en jeu apparaissent directement influences par l'organisation de particules elementaires au sein des agregats. La comparaison des processus de transformation de phase (zircone tetragonal zircone monoclinique) qui s'operent lors de recuits de poudres montre encore des comportements specifiques. Alors que la transformation de phase apparait assez progressivement pour le xerogel, voire tres progressivement dans le cas de l'aerogel, le precipite se caracterise par une transformation abrupte sur un laps de temperature restreint.
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Fehr, Carlos. "Etude des propriétés structurales des phases mésomorphes et cristallines de composés de type 4-n-alky-4'-cyanobiphényl confinés dans des milieux poreux à structure désordonnée." Montpellier 2, 2002. http://www.theses.fr/2002MON20141.
Full textBook chapters on the topic "Sol-gel phase transition"
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Munch, J. P., M. Delsanti, M. Adam, and D. Durand. "Sol-Gel Transition : An Experimental Study." In Phase Transitions in Soft Condensed Matter, 331–34. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-0551-4_35.
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Reher, E. O., R. Schnabel, and V. Schulze. "Use of Amplitude and Frequency Spectrometry for Determining the Sol-Gel Phase Transition." In Third European Rheology Conference and Golden Jubilee Meeting of the British Society of Rheology, 403–6. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0781-2_138.
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Tang, Dian, Xiao Kang Wang, and Teng Zhang. "Phase Transitions in Binary SnO2-CeO2 System Prepared by a Sol-Gel Method." In Solid State Phenomena, 555–60. Stafa: Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/3-908451-25-6.555.
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Tadeu Cestarolli, Dane, and Elidia Maria Guerra. "Vanadium Pentoxide (V2O5): Their Obtaining Methods and Wide Applications." In Transition Metal Compounds - Synthesis, Properties, and Application. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96860.
Full textAbstract:
The first synthesis of pentoxide vanadium (V2O5) as gel completed 135 years in 2020. Since its first synthesis, the V2O5 has attracted attention over the years in different areas in science and technology. There are several possibilities to obtain V2O5 resulting in different structures. Among these methods, it is possible to mention the sol–gel, hydrothermal/solvothermal synthesis, electrospinning, chemical vapor deposition (CVD), physical vapor deposition (PVD), template-based methods, reverse micelle techniques, Pechini method and electrochemical deposition that can be considered as the great asset for its varied structures and properties. Progress towards obtaining of different structures of V2O5, and phases have been resulted in lamellar structure with wide interlayer spacing, good chemical and thermal stability and thermoelectric and electrochromic properties. Throughout this advancement, its performance for industrial applications have made a strong candidate in electrochromic devices, photovoltaic cell, reversible cathode materials for Li batteries, supercapacitor, among others. This chapter will be to assist an updated review since the first synthesis up to current development.
Conference papers on the topic "Sol-gel phase transition"
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Jaiswal, Shivendra Kumar, and Jitendra Kumar. "Sol-Gel Synthesis and Magnetic, Optical and Impedance Behaviour of Strontium Ferrite Powder." In ASME 2011 International Manufacturing Science and Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/msec2011-50067.
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An attempt has been made to synthesize SrFeO3-δ powder by sol-gel process involving oxalate formation, its digestion for 4h, drying at 150°C for 24h, and decomposition at 800°C for 10h. The resulting powder is shown to a) exhibit a single phase with a perovskite-type cubic structure and lattice parameter a = 3.862±0.002A˚, b) contain irregular shape particles, and c) display optical absorption peaks corresponding to charge transfer from oxygen to iron (3.73 and 3.41eV), t2g to eg transition of Fe3+ (1.57eV), and crystal field (3d-3d) charge transfer of Fe3+ (1.25eV). Impedance over a wide frequency range of 20Hz-2MHz at 118–318K has contributions from two parallel ‘RC’ circuits belonging to bulk and grain boundaries with the later displaying significant space charge polarization. The relaxation time of polarization follows an Arrhenius behaviour (τ = τo exp[Ea/kBT]) with τo as ∼10−8s and activation energy Ea as ∼50meV. Further, the sample having magnetic character with transition temperature as 853K, coercivity (Hc) = 3748Oe and magnetization 0.09 μB per iron atom (at 17kOe). The zero field cooled and field cooled magnetization versus temperature data in conjunction with constricted hysteresis loops near the origin suggest core-shell morphology for the particles, core being antiferromagnetic with net uncompensated moment and shell conforming to disordered disposition of spins.
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Grzenda, Michael, Arielle Gamboa, James Mercado, Lin Lei, Jennifer Guzman, Lisa C. Klein, Andrei Jitianu, and Jonathan P. Singer. "Parametric Control of Melting Gel Morphology and Chemistry via Electrospray Deposition." In ASME 2021 16th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/msec2021-63347.
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Abstract Melting gels are a class of hybrid organic-inorganic, silica-based sol-gels which are solid below their glass transition temperatures, near room temperature, but show thermoplastic behavior when heated. While this phase change can be repeated multiple times, heating the gel past its consolidation temperature, typically above 130 °C, initiates an irreversible reaction that produces highly crosslinked glassy organic/inorganic materials via hydrolysis and polycondensation. This ability makes melting gels uniquely compatible with processing techniques inaccessible to other sol-gels. By properly tuning their properties, it should be possible to create protective coatings for electronics and anti-corrosive coatings for metals that are highly hydrophobic and insulating. However, melting gel consolidation reactions are highly dependent on charge interactions, raising the question of how these materials will respond to a processing technique, like electrospray deposition (ESD), which is dependent on charge delivery. In this study, we focus on the role that substrate temperature and charge polarity play on film morphology, consolidation chemistry, and surface properties when processing via ESD. Optical images, film thickness measurements, and FTIR were used to characterize the sprayed melting gel with the goal of developing a robust processing space for producing highly cross linked, hydrophobic, dielectric coatings.