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Comportamento de cristalização de lipídios estruturados obtidos a partir de gordura do leite e óleo de girassol; Crystallization behavior of structured lipids by chemical interesterification of milkfat and sunflower oil

RODRIGUES-RACT, Juliana Neves; COTTING, Lucia Nazareth; POLTRONIERI, Tatyane Pereira; SILVA, Roberta Claro da; GIOIELLI, Luiz Antonio
Fonte: Sociedade Brasileira de Ciência e Tecnologia de Alimentos Publicador: Sociedade Brasileira de Ciência e Tecnologia de Alimentos
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
581.53918%
A finalidade do estudo foi avaliar o comportamento de cristalização de misturas binárias de gordura do leite e óleo de girassol em diversas proporções, bem como de seus correspondentes lipídios estruturados obtidos por interesterificação química. Foram usados conteúdo de gordura sólida, consistência, ponto de amolecimento e microscopia sob luz polarizada para avaliar as misturas antes e após a interesterificação. A adição de óleo de girassol e a interesterificação modificaram a cristalização da gordura do leite, pelos efeitos de diluição e rearranjo dos triacilgliceróis. Arquivos de vídeo em formato WMV foram compilados para estudar a cristalização a 20 ºC. Os vídeos tornaram possível a observação da estrutura cristalina formada e representaram uma ferramenta de grande importância para a pesquisa de cristalização de óleos e gorduras.; The aim of this study was to evaluate the crystallization behavior of binary mixtures of milkfat and sunflower oil in different ratios and their respective structured lipids obtained by chemical interesterification. Solid fat content, consistency, softening point and polarized light microscopy were used to analyze the mixtures before and after interesterification. The addition of sunflower oil and the interesterification changed the milkfat crystallization...

Comportamento de cristalização de lipídios estruturados por interesterificação química de banha e óleo de soja; Crystallization behavior of structured lipids by chemical interesterification of lard and soybean oil

SILVA, Roberta Claro da; ESCOBEDO, Jonas Peixoto; GIOIELLI, Luiz Antonio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
579.67977%
The aim of this study was to evaluate the crystallization behavior of binary mixtures of lard and soybean oil in different ratios and their respective structured lipids obtained by chemical interesterification. Crystallization kinetics and polarized light microscopy were used to analyze the mixtures before and after interesterification. The addition of soybean oil changed the lard crystallization, by the effect of the dilution. Crystal diameter increased, while the number of crystals decreased, as a function of temperature. Interesterification resulted in the formation of fewer crystals, with larger diameter in comparison with the original mixtures.; FAPESP; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); CNPq

Physico-chemical properties of Brazilian cocoa butter and industrial blends. Part II - Microstructure, polymorphic behavior and crystallization characteristics

Ribeiro, A. P. B.; Correa Basso, R.; Goncalves, L. A. G.; Gioielli, L. A.; Oliveira dos Santos, A.; Pavie Cardoso, L.; Guenter Kieckbusch, T.
Fonte: INST GRASA SUS DERIVADOS; SEVILLE Publicador: INST GRASA SUS DERIVADOS; SEVILLE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
483.09367%
The microstructural behavior of industrial standardized cocoa butter samples and cocoa butter samples from three different Brazilian states is compared. The cocoa butters were characterized by their microstructural patterns, crystallization kinetics and polymorphic habits. The evaluation of these parameters aided in establishing relationships between the chemical compositions and crystallization behavior of the samples, as well as differentiating them in terms of technological and industrial potential for use in tropical regions.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [Proc. 2009/53006-0, Proc. 2010/18504 -7]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)

Thermal behavior of ara double dagger a oil (Psidium cattleianum Sabine)

Kobelnik, Marcelo; Cassimiro, Douglas Lopes; Dias, Diogenes dos Santos; Ribeiro, Clovis Augusto; Crespi, Marisa Spirandeli
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 1281-1286
ENG
Relevância na Pesquisa
472.6435%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); The ara double dagger A is a well-known fruit, which belongs to the Myrtaceae family, Psidium cattleianum Sabine species, frequently found in the southern region of Brazil. The extraction of ara double dagger a oil was carried out from seeds, and the fatty acid profile of this oil indicates the predominant presence of linoleic acid (81.38%). Thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (DSC) were used to characterize this oil. In addition, this oil was evaluated by DSC from 25 to -60 A degrees C, where the crystallization behavior was verified. Details concerning thermal decomposition as well as data of kinetic parameters of these stages have been described here. The kinetic behavior of the thermal decomposition was evaluated from several heating rates with mass samples of 5 and 20 mg in open crucibles under nitrogen and synthetic air atmospheres.

Magnetic resonance study of the crystallization behavior of InF3-based glasses doped with Cu2+, Mn2+ and Gd3+

Franco, R. W A; Lima, J. F.; Magon, C. J.; Donoso, J. P.; Messaddeq, Y.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 3414-3422
ENG
Relevância na Pesquisa
473.1623%
The crystallization of fluoroindate glasses doped with Gd3+, Mn2+ and Cu2+ heat treated at different temperatures, ranging from the glass transition temperature (Tg) to the crystallization temperature (Tc), are investigated by electron paramagnetic resonance (EPR) and 19F nuclear magnetic resonance (NMR). The EPR spectra indicate that the Cu2+ ions in the glass are located in axially distorted octahedral sites. In the crystallized glass, the g-values agreed with those reported for Ba2ZnF6, which correspond to Cu2+ in a tetragonal compressed F- octahedron and to Cu2+ on interstitial sites with a square-planar F- co-ordination. The EPR spectra of the Mn2+ doped glasses exhibit a sextet structure due to the Mn2+ hyperfine interaction. These spectra suggest a highly ordered environment for the Mn2+ ions (close to octahedral symmetry) in the glass. The EPR spectra of the recrystallized sample exhibit resonances at the same position, suggesting that the Mn2+ ions are located in sites of highly symmetric crystalline field. The increase of the line intensity of the sextet and the decrease of the background line in the thermal treated samples suggest that the Mn2+ ions move to the highly ordered sites which contribute to the sextet structure. The EPR spectra of the Gd3+ doped glasses exhibit the typical U-spectrum of a s-state ion in a low symmetry site in disordered systems. The EPR of the crystallized glasses...

Avaliação e adequação do comportamento de gorduras equivalentes de manteiga de cacau para chocolates; Evaluation and adequacy of the behavior of cocoa butter equivalents for chocolate

Ingrid Franco de Oliveira
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/03/2013 PT
Relevância na Pesquisa
482.94508%
Gorduras equivalentes de manteiga de cacau (CBEs) são utilizadas nas formulações de chocolates, substituindo parte da manteiga de cacau (MC). Embora as CBEs sejam compatíveis com a MC é importante um estudo detalhado a fim de se conhecer as propriedades de cristalização, fusão e estabilidade dos cristais, uma vez que as mesmas alteram a qualidade dos chocolates. Este estudo objetivou aumentar o conhecimento sobre CBEs e propor alteração do comportamento de fusão e cristalização de uma CBE escolhida. Sendo assim, foram caracterizadas quatro CBEs, com base em uma MC usada como padrão. As análises utilizadas para a caracterização foram índices de qualidade e de identidade, composição em ácidos graxos, índice de iodo, índice de saponificação, ponto de fusão, teor de sólidos por Ressonância Magnética Nuclear (RMN), isoterma de cristalização a 17,5°C por RMN, eventos de cristalização por Calorimetria Diferencial de Varredura (DSC), eventos de fusão por DSC em quatro tempos de armazenamento a 25°C (0, 4, 8 e 24 horas) e análise por difração de Raios-X. Adicionou-se 0,3% de triestearato de sorbitana (STS) às CBEs e o efeito do STS foi avaliado por meio de isotermas a 17,5°C, eventos de fusão por DSC em quatro tempos de armazenamento a 25°C (0...

Estudo do efeito da composição dos ésteres de ácidos graxos de sorbitanas comerciais na cristalização de óleo de palma refinado; Study of the effect of the commercial sorbitan fatty acid esters composition on crystallization of refined palm oil

Camilia Aoyagui dos Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/03/2013 PT
Relevância na Pesquisa
485.6565%
O óleo de palma possui lenta cristalização devido à alta energia livre de ativação de nucleação, atribuída às interações intermoleculares entre a estearina e a oleína e à presença dos diacilgliceróis. Aditivos podem ser adicionados ao óleo de palma na tentativa de modificar o seu comportamento de cristalização, adequando o seu uso aos processos industriais. Dentre esses aditivos se destacam os emulsificantes, que diferentemente da sua função usual, podem ser utilizados para alterar a estrutura cristalina e contribuir inclusive para a estabilidade de formas polimórficas desejadas nos óleos e gorduras onde são aplicados. Os ésteres de ácidos graxos de sorbitana têm demonstrado influência na morfologia dos cristais e na textura de misturas de óleos à base de palma. No entanto, estudos indicaram que os monoésteres de ácidos graxos de sorbitana disponíveis comercialmente possuíam diferentes composições em mono-, di- e triésteres de ácidos graxos de sorbitana. Esta variabilidade pode dificultar a comparação de resultados obtidos de cristalização de óleos e gorduras após adição destes emulsificantes entre os diversos estudos já realizados. O objetivo deste trabalho foi determinar a composição de vários ésteres de ácidos graxos comerciais...

Avaliação da incorporação de emulsificantes sobre as propriedades de cristalização de gorduras industriais; Evaluation of emulsifiers addition on the crystallization properties of industrial fats

Maria Aliciane Fontenele Domingues
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/09/2013 PT
Relevância na Pesquisa
478.41242%
A cristalização de gorduras é um fator crítico associado à estruturação e propriedades de grande parte dos alimentos. No Brasil, as questões controversas acerca do papel dos ácidos graxos trans na alimentação ocasionaram modificações progressivas na legislação e no uso industrial de gorduras, levando à substituição das gorduras parcialmente hidrogenadas por gorduras interesterificadas, fracionadas ou blends. Considerando que este processo de substituição foi ampliando, os problemas de comportamento de cristalização devido à não adequação das novas frações gordurosas são inúmeros e agravados, principalmente, pelas diferenças climáticas regionais e condições de transporte e estocagem. Logo, a adequação da cinética de cristalização destas bases gordurosas é de extrema importância para que o uso das mesmas possa ser ajustado às limitações dos processos industriais e para melhorar o controle de etapas de processamento que envolva recristalização da fração gordurosa, garantindo a qualidade do produto final. Caso contrário, os tempos de processamento e equipamentos já padronizados precisam ser alterados segundo as características da gordura utilizada. Emulsificantes são aditivos funcionais de extrema importância na indústria de alimentos...

Efeito da adição de monoésteres de sorbitana e de estearina da manteiga de cacau como modificadores de cristalização na produção de chocolate; Effect of sorbitan monoesters and cocoa butter stearin additions as crystallization modifiers in the chocolate production

Monise Helen Masuchi
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/04/2014 PT
Relevância na Pesquisa
490.1933%
O comportamento de cristalização da manteiga de cacau (MC) é um importante parâmetro estrutural no desenvolvimento de chocolates com significativa resistência à formação do fat bloom ¿ um defeito comum em chocolates, caracterizado pela superfície com aparência esbranquiçada e perda de brilho devido à recristalização lipídica local. Com o objetivo de controlar e estabilizar a formação cristalina da MC em chocolates, neste trabalho avaliou-se a influência da adição de monoésteres de sorbitana (monolaurato, monopalmitato, monoestearato e monooleato) e de estearina da manteiga de cacau (obtida por fracionamento da MC com solvente) no comportamento de cristalização e consistência, assim como na microestrutura e no polimorfismo da MC. Monoésteres de sorbitana em três diferentes concentrações (0,5; 1,0 e 1,5% m/m) foram adicionados em MC e seus possíveis efeitos como modificadores de cristalização foram avaliados. O monoestearato de sorbitana (SMS) apresentou-se como o estruturante mais efetivo entre todos os emulsificantes testados, cuja atuação foi atribuída a sua solubilidade em meio orgânico e capacidade de auto-montagem. A adição de 0,5% de SMS em MC promoveu aumento relevante na temperatura de início de cristalização da MC (de 19...

Previsão de parâmetros de cristalização de blends de gorduras para uso específico por redes neurais artificiais; Prediction of crystallization parameters of fat blends for specific use by artificial neural network

Rita de Kássia de Almeida Garcia
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/07/2014 PT
Relevância na Pesquisa
479.74645%
Óleos e gorduras são submetidos ao processo de blending para alcançar características específicas, visando sua aplicação em variados produtos. Redes neurais artificiais (RNA) têm sido utilizadas para otimizar o processo de formulação de gorduras baseado no conteúdo de gordura sólida (SFC). Além do SFC, a cinética de cristalização das gorduras ou blends influencia diretamente nas condições de processamento, bem como nas características e qualidade dos produtos elaborados. Nesse contexto, o objetivo deste trabalho foi construir e treinar RNAs capazes de prever parâmetros de cristalização de blends de gorduras. Foram treinadas duas RNAs usando blends contendo gorduras interesterificadas de soja, óleos de soja, palma e palmíste como matérias-primas. No treinamento, além dos dados de SFC, foram utilizados os parâmetros de cristalização tempo de indução (T1), tempo médio (T2), tempo final (T3) e SFC máximo (%), obtidos pelas isotermas de cristalização a 25°C. Além disso, como avaliação, foi verificada a capacidade das RNAs em predizer os parâmetros de cristalização de formulações sugeridas pelas RNAs para aplicação em recheio de biscoitos e uso geral. Como resultados, as RNAs se mostraram capazes de prever os parâmetros de cristalização para os blends elaborados com as diferentes matérias-primas...

Physico-chemical properties of Brazilian cocoa butter and industrial blends. Part II - Microstructure, polymorphic behavior and crystallization characteristics

Ribeiro, A. P. B.; Correa Basso, R.; Goncalves, L. A. G.; Gioielli, L. A.; Oliveira dos Santos, A.; Pavie Cardoso, L.; Guenter Kieckbusch, T.
Fonte: Inst Grasa Sus Derivados; Seville Publicador: Inst Grasa Sus Derivados; Seville
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
480.51914%
The microstructural behavior of industrial standardized cocoa butter samples and cocoa butter samples from three different Brazilian states is compared. The cocoa butters were characterized by their microstructural patterns, crystallization kinetics and polymorphic habits. The evaluation of these parameters aided in establishing relationships between the chemical compositions and crystallization behavior of the samples, as well as differentiating them in terms of technological and industrial potential for use in tropical regions.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The role of defect microstructure in the crystallization behavior of metallocene and MgCl2-supported Ziegler-Natta isotactic poly(propylenes)

Alamo,Rufina G.
Fonte: Associação Brasileira de Polímeros Publicador: Associação Brasileira de Polímeros
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2003 EN
Relevância na Pesquisa
477.1052%
The intermolecular defect distribution of poly(propylenes) of the Ziegler-Natta (ZN) and metallocene (M) types is assessed by classical fractionation and analysis of the fractions by GPC and 13C NMR. In addition, the linear growth rates, a property sensitive to differences in defects distribution in the poly(propylene) chain, are used to infer the stereoblock-like intramolecular distribution of defects in industrial type ZN iPPs and their fractions. The behavior of fractions from a matched metallocene iPP provide direct evidence of the single-site nature of the catalyst. Metallocene poly(propylenes) enable a quantitative assessment of the molecular, thermodynamic and kinetic factors that govern the formation and concentrations of the a and g polymorphs. Short continuous crystallizable sequences and high crystallization temperatures favor the formation of this polymorph in homo poly(propylenes) and random propylene copolymers. Differences in the partitioning of the comonomer between the crystalline and non-crystalline regions leads to contents of the gamma phase that differ among the copolymers at any given crystallization temperature. Qualitatively these differences can be used to assess the degree to which a counit participates in the crystallite.

Study of crystallization behavior of poly(phenylene sulfide)

Nohara,Liliana B.; Nohara,Evandro L.; Moura,Andreza; Gonçalves,Joseane M. R. P.; Costa,Michelle L.; Rezende,Mirabel C.
Fonte: Associação Brasileira de Polímeros Publicador: Associação Brasileira de Polímeros
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
Relevância na Pesquisa
481.53918%
Poly(phenylene sulfide) (PPS) is an engineering thermoplastic polymer that presents high temperature resistance (glass transition temperature around 85 ºC and melting point at 285 ºC). These properties combined with its mechanical properties and its high chemical resistance allows its use in technological applications such as molding resins and as matrix for structural thermoplastic composites. During the manufacture of thermoplastic composites, the polymer is exposed to repeated melting, quenching and crystallization processes. The properties of semicrystalline polymers, such as PPS, depend on its crystallization behavior. This work deals with the PPS crystallization kinetics under different thermal cycles. This study was performed under isothermal conditions in a differential scanning calorimetry (DSC), coupled to Perkin Elmer crystallization software referred to as Pyris Kinetics - Crystallization. The results were correlated with microscopic analyses carried out in a polarized light microscope, equipped with a controlled heating and cooling accessory. In this case, the experimental conditions were the same adopted for the DSC analyses. From the results, parameters could be established to be used in the composite manufacture.

Effect of Preparation Methods on Crystallization Behavior and Tensile Strength of Poly(vinylidene fluoride) Membranes

Liu, Jie; Lu, Xiaolong; Wu, Chunrui
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 21/11/2013 EN
Relevância na Pesquisa
484.04316%
Poly(vinylidene fluoride) (PVDF) membranes were prepared by non solvent induced phase separation (NIPS), melt spinning and the solution-cast method. The effect of preparation methods with different membrane formation mechanisms on crystallization behavior and tensile strength of PVDF membranes was investigated. Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray diffraction (XRD) were employed to examine the crystal form of the surface layers and the overall membranes, respectively. Spherulite morphologies and thermal behavior of the membranes were studied by polarized light optical microscopy (PLO) and differential scanning calorimetry (DSC) separately. It was found that the crystallization behavior of PVDF membranes was closely related to the preparation methods. For membranes prepared by the NIPS method, the skin layers had a mixture of α and β phases, the overall membranes were predominantly α phase, and the total crystallinity was 60.0% with no spherulite. For melt spinning membranes, the surface layers also showed a mixture of α and β phases, the overall membranes were predominantly α phase. The total crystallinity was 48.7% with perfect spherulites. Whereas the crystallization behavior of solution-cast membranes was related to the evaporation temperature and the additive...

The Effect of Chain Structures on the Crystallization Behavior and Membrane Formation of Poly(Vinylidene Fluoride) Copolymers

Ma, Wenzhong; Yuan, Haoge; Wang, Xiaolin
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 19/05/2014 EN
Relevância na Pesquisa
481.53918%
The crystallization behaviors of two copolymers of PVDF were studied, and the effect of copolymerized chains on the crystallization behavior was investigated. The results indicated that both copolymers had a lowered crystallization temperature and crystallinity. The crystallization rate was improved by the copolymer with symmetrical units in PVDF chains, but hindered by asymmetrical units, compared with the neat PVDF. The symmetrical units in PVDF chains favored the β-crystals with fiber-like structures. According to the solubility parameter rule, methyl salicylate (MS) can be chosen as a diluent for PVDF copolymers. Both diluted systems had liquid-liquid (L-L) regions in the phase diagrams, which was due to the lowered crystallization temperature.

Crystallization behavior of poly(lactide)/poly(β-hydroxybutyrate)/talc composites.

TRI, Phuong Nguyen; DOMENEK, Sandra; GUINAULT, Alain; SOLLOGOUB, Cyrille
Fonte: Wiley Publicador: Wiley
EN
Relevância na Pesquisa
476.4276%
The authors thank Dr. Patrice Lefrançois (CNAM) for SEM observations. They are also grateful to Pr. Jack R. Plimmer USDA, Agricultural Research Service, USA for his discussions during this work.; The morphology and miscibility of commercial poly(lactide) (PLA)/poly(b-hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infra-red spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improve-ment, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger’s equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt.

Effect of changing the rare earth cation type on the structure and crystallization behavior of an aluminoborosilicate glass

Quintas, Arnaud; Caurant, Daniel; Majérus, Odile; Dussossoy, Jean-Luc; Charpentier, Thibault
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/04/2011
Relevância na Pesquisa
484.95312%
An aluminoborosilicate glass, containing high amount of rare earth (RE) accordingly to the following composition 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 - 12.19 Na2O - 4.84 CaO - 3.19 ZrO2 - 16.35 RE2O3 (wt.%), is currently under study for the immobilization of nuclear waste solutions. In this work, we wanted to investigate the effect of changing the RE cation type on the glass structure and on its crystallization behavior. For this purpose, a glass series was elaborated in which the nature of the RE is varying from lanthanum to lutetium. In this glass series, only little effect was observed on the glass structure. On the contrary, a strong impact was put in evidence on the crystallization behavior through different heat treatments. A slow cooling of the melt at 1^/circC/min, revealed significant crystallization of apatite Ca2RE8(SiO4)6O2 in sample containing rare earths with ionic radii close to that of calcium. Another heat treatment consisting of successive nucleation and growth stages, performed to force the crystallization in the bulk and reduce any surface crystallization effect, put in evidence the existence of a strongly heterogeneous second rare earth rich silicate phase for samples containing RE with low ionic radius (from Y to Lu).; Comment: 4 pages; XXIst International Congress on Glass (ICG 2007)...

Dynamical and structural aspects of the cold crystallization of poly(dimethylsiloxane) (PDMS)

Lund, Reidar; Alegría, Ángel; Goitiandia, Luis; Colmenero de León, Juan; González, Miguel A.; Lindner, Peter
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 572559 bytes; application/pdf
ENG
Relevância na Pesquisa
487.4593%
13 pages.; A detailed study of the dynamical and structural aspects of the cold crystallization behavior of highly flexible poly(dimethylsiloxane)(PDMS) is presented. In order to understand the complete behavior, before, under and after crystallization, a wide range of experimental techniques have been employed. A particular emphasis is made on the interplay between dynamical and structural effects and how the properties of the amorphous phase evolve during the crystallization. This is highlighted by combining mobility sensitive techniques, involving broadband dielectric spectroscopy (BDS) and differential scanning calorimetry, with neutron scattering: wide and small-angle neutron scattering (WANS/SANS) which are sensitive to the relative ordering of the atoms. In this way, we are able to compare the structure associated with crystal formation with the evolution and modification of the amorphous phase. The kinetics deduced from WANS points toward a classical nucleation and growth behavior closely following a Avrami-like growth with an exponent of about n = 3 which is expected for athermal nucleation from fixed centers followed by three-dimensional crystal growth. Furthermore, the amorphous phase (deduced from BDS) decays in parallel with the emergence of the crystalline phase (from WANS/SANS) without any shift in the characteristic relaxation time. However a careful comparison of the crystallization at short times indicates that the amorphous phase seems to be affected before any measurable crystallization is detected by WANS. Although this might be compatible with the existence of mesomorphic phase...

Pronounced asymmetry in the crystallization behavior during constant heating and cooling of a bulk metallic glass-forming liquid

Schroers, Jan; Masuhr, Andreas; Johnson, William L.; Busch, Ralf
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/11/1999
Relevância na Pesquisa
477.1052%
The crystallization behavior of the supercooled bulk metallic glass-forming Zr41Ti14Cu12Ni10Be23 liquid was studied with different heating and cooling rates. A rate of about 1 K/s is sufficient to suppress crystallization of the melt upon cooling from the equilibrium liquid. Upon heating, in contrast, a rate of about 200 K/s is necessary to avoid crystallization. The difference between the critical heating and cooling rate is discussed with respect to diffusion-limited growth taking classical nucleation into account. The calculated asymmetry of the critical heating and cooling rate can be explained by the fact that nuclei formed during cooling and heating are exposed to different growth rates.

Study of the crystallization behavior of polyethylene oxide in compatibilized and uncompatibilized polypropylene/polyethylene oxide blends

Iyer, Subramanian
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
586.359%
Compatibilization of incompatible isotactic polypropylene (iPP)/polyethylene oxide (PEO) is studied with an emphasis on the crystallization behavior of polyethylene oxide. An attempt is made to correlate the crystallization data for PEO obtained from optical microscopy, differential scanning calorimetry, x-ray diffraction, infrared spectroscopy and dynamic mechanical analysis. PEO and iPP are incompatible in the temperature range -50C to 200C. iPP was used as the matrix while PEO was used as the dispersed phase. Experimental observations demonstrated that PEO underwent fractionated crystallization in the blends in the temperature region from -10C to 40C when cooled at a rate of 10C/min. PEO domains nucleated homogeneously as well as heterogeneously in these blends. Larger domains (30-100 microns) crystallized at higher temperatures (heterogeneous nucleation), while smaller domains (10-60 microns) crystallized at lower temperatures (homogeneous nucleation). Heterogeneous nucleation occurred both thermally, and athermally. The graft copolymer, polypropylene-graft-maleic anhydride-graft-polyethylene glycol was used to increase compatibility between iPP and PEO. Three blends systems were studied; iPP and PEO, polypropylene-graft-maleic anhydride and PEO and polypropylene-graft-maleic anhydride-graft-polyethylene oxide and PEO. An increase in the concentration of PEO in the blends increased its crystallinity. However there was a decrease in the crystallinity of PEO...