Propriedades estruturais de géis de sílica preparados com adições de dodecil sulfato de sódio

This work aims to study the structural characteristics of silica gels obtained from the acid hydrolysis of tetraethoxysilane (TEOS) in water solutions with different concentrations of sodium dodecyl sulfate (SDS). The structural characteristics were studied in stages ranging from the wet gel to the dry stages of the gels (aerogels and xerogels). Aerogels were obtained by ambient pressure drying (APD) after silylation process using trimethylchlorosilane (TMCS) as silylating agent. Xerogels were obtained by conventional evaporating the liquid phase from non silylated gels. The samples were characterized by nitrogen adsorption and small angle X-ray scattering (SAXS). The structure of the wet gels and of the aerogels prepared with the surfactant exhibited characteristics of mass-fractal structures with fractal dimension D in the range 2.1-2.2 for the wet gels and 2.3-2.4 for the aerogels. The characteristic size  of the fractal domain reduces while the size a0 of the primary silica particle composing the fractal structure increases with the drying of the gels, in a process in which share of the porosity is eliminated. Aerogels exhibited typical values for the specific surface of 900 m2g-1 and of 3.5 cm3.g-1 for the total pore volume. These values are correspondingly comparable to those of the aerogels prepared by supercritical drying, since the silylation process replaces hydrophilic –OH groups by hydrophobic –Si-R3 ones, inhibiting the porosity elimination on drying. The silica particle size also increases lightly with the silylation because the attachment of the –Si-R3 groups on the silica surface. The pore size distribution curves of the aerogels are similar for all samples exhibiting a maximum in around 40 nm, independent the concentration of surfactant. This suggests that the characteristic size of 40 nm is due to the association of surfactant micelles... (Complete abstract click electronic access below)

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caracterização e aplicação da Blenda PEDOT : PSS/PVA na construção de eletrodos transparentes e dispositivos eletroluminescentes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Aplicação da membrana de látex natural (NRL) como suporte para cultura das células osteogênicas MC3T3-E1 para regeneração óssea guiada (GBR)

Pós-graduação em Biotecnologia - IQ

Aperfeiçoamento em equipamento para digestão de amostras por via úmida

Aperfeiçoamento em equipamento para digestão de amostras por via úmida. É descrito um aperfeiçoamento em equipamento para digestão de amostras por via úmida que emprega tubos de digestão (20) fechados não encapsulados e aquecimento condutivo que possibilita a rápida decomposição de amostras botânicas, alimentícias, clínicas, ambientais e similares, promovendo um gradiente de temperatura em direção à parte superior do tubo de digestão, permitindo que a temperatura da fase gasosa seja inferior à da fase líquida, de forma que as digestões são realizadas à pressão pouco elevada e, consequentemente, os tubos de digestão utilizados podem ter paredes menos espessas, permitindo o rápido aquecimento e resfriamento das amostras, bem como baixo custo de operação e manutenção, simplicidade, alta frequência analítica,; redução do consumo de reagentes e diminuição da geração de resíduos, dito equipamento provido de um gabinete (10) que evita a contaminação da atmosfera do laboratório por vapores ácidos e a perda dos componentes voláteis da amostra durante o aquecimento

Spontaneous symmetry breaking in a spin-orbit-coupled f=2 spinor condensate

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evolution of Goldstone mode in binary condensate mixtures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ra-226 and Ra-228 in mineral waters of southeast Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efficiency comparison of hyperbranched polymers as toughening agents for a one-part epoxy resin

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Contribution of different segments of the gastrointestinal tract to digestion in growing Saanen goats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Origin of spin incommensurability in hole-doped S=1 Y2-xCaxBaNiO5 chains

Spin incommensurability (IC) has been recently experimentally discovered in the hole-doped Ni-oxide chain compound Y2-xCaxBaNiO5 [G. Xu et al., Science 289, 419 (2000)]. Here a two orbital model for this material is studied using computational techniques. Spin IC is observed in a wide range of densities and couplings. The phenomenon originates in antiferromagnetic correlations across holes dynamically generated to improve hole movement, as it occurs in the one-dimensional Hubbard model and in recent studies of the two-dimensional extended t-J model. The close proximity of ferromagnetic and phase-separated states in parameter space is also discussed.

Análise estrutural de aerogéis via espalhamento de luz a baixo ângulo

The sol-gel process is a method for obtaining vitreous or vitro-ceramic materials which, are prepared a sol and by drying the liquid phase. This technique has been used extensively for the preparation of glassy gels, films, fibers and particles from the hydrolysis and polycondensation reactions of metal alkoxides. The usual methods for drying are: evaporation drying (xerogels), freeze drying (criogéis) and via supercritical CO2 extraction (aerogels). In the present work, we studied the preparation of silica gels by the sol-gel process from the hydrolysis of alkoxides tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTS). The hydrolysis was promoted from GPTS and TEOS in proportion (4: 1) under acidic conditions. The hydrolysis reaction was promoted inside a Becker at room temperature. After hydrolyses the prepared sol had pH 2, and kept under mechanical agitation for a period of 1 hour. In order to accelerate the polycondensation reaction, the pH was corrected to a value near 5 by slowly adding NH4OH. Then the sols were leaked in sealed polycarbonate containers and maintained for 20 days at 40°C for gelation. Silica aerogels were prepared via supercritical CO2 extraction of the wet gel at temperature and pressure higher than 31°C and 74 atm, in an autoclave specially developed for the process. The structural characteristics were studied in the dry gel (aerogel). Aerogels were then characterized by nitrogen adsorption and small angle light scattering. The nitrogen adsorption data were analyzed for the determination of the BET specific surface (SBET), the total pore volume Vp, the pore mean size (lP=4Vp/SBET), the particle mean size (lS) and the pore size distribution (PSD). And the data from small angle light scattering were analyzed to determine the correlation function (γ'), the area per unit volume (S/V), average pore size (l ) and the average particle size...

Aluminas macro-mesoporosas produzidas pelo método sol-gel para aplicação em catálise heterogênea

Pós-graduação em Química - IQ

Investigação das propriedades de transporte da fase ferroelétrica de Mott-Hubbard em condutores moleculares

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese de aluminas macro-mesoporosas pelo método sol-gel acompanhado de separação de fases

Pós-graduação em Química - IQ