Small-angle X-ray and nuclear-magnetic resonance study of siloxane-PMMA hybrids prepared by the sol-gel process

Transparent siloxane-polymethylmethacrylate (PMMA) hybrids were synthesized by the sol-gel process through hydrolysis of methacryloxyproyltrimethoxysilane (TMSM), tetramethoxysilane (TMOS) and polymerization of methylmethacrylate (MMA) using benzol peroxide (BPO) as catalyst. These composites have a good chemical stability due to the presence of covalent bonds between the inorganic (siloxane) and organic (PMMA) phases. The effects of siloxane content, pH of the initial sol and BPO content on the structure of the dried gels were analyzed by small-angle X-ray scattering (SAXS). SAXS results revealed the presence of an interference (or correlation) peak at medium q-range for all compositions, suggesting that siloxane groups located at the ends of PMMA chains form isolated clusters that are spatially correlated. The average intercluster distance - estimated from the q-value corresponding to the maximum in SAXS spectra - decreases for samples prepared with increasing amount of TMSM-TMOS. This effect was assigned to the expected increase in the number density of siloxane groups for progressively higher siloxane content. The increase of BPO content promotes a more efficient polymerization of MMA monomers but has no noticeable effect on the average intercluster distance. High pH favors polycondensation reactions between silicon species of both TMOS and TMSM silicon alcoxides, leading to a structure in which all siloxane clusters are bonded to PMMA chains. This effect was confirmed by Si-29 nuclear-magnetic resonance (NMR) measurements.

Study of the annealing temperature effect on the structural and luminescent properties of SrWO4:Eu phosphors prepared by a non-hydrolytic sol-gel process

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

Active planar waveguides based on sol-gel Er3+-doped SiO2-ZrO2 for photonic applications: Morphological, structural and optical properties

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

Broadband NIR Emission in Sol-Gel Er(3+)-Activated SiO(2)-Ta(2)O(5) Glass Ceramic Planar and Channel Waveguides for Optical Application

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

New strategies in the preparation of exfoliated thermoplastic starch-montmorillonite nanocomposites

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

Speciation of lead in seawater and river water by using Saccharomyces cerevisiae immobilized in agarose gel as a binding agent in the diffusive gradients in thin films technique

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

Thermo-Reversible Sol-Gel Transition of Surface Modified Titanium Poly Oxo Building Blocks

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

Corrosion protection of stainless steel by polysiloxane hybrid coatings prepared using the sol-gel process

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Characterization of nanosized ZnAl2O4 spinel synthesized by the sol-gel method

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

Thermo-reversible sol-gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol-gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 degrees C of titanium tetraisopropoxide (Ti((OPr)-Pr-i)(4)) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 degrees C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of approximate to 2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the then-no-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between -SO3 groups of p-toluene sulfonic acid. (C) 2009 Elsevier Ltd. All rights reserved.

Zirconia foams prepared by integration of the sol-gel method and dual soft template techniques

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Use of Saccharomyces cerevisiae immobilized in agarose gel as a binding agent for diffusive gradients in thin films

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

Characterization of Staphylococcus aureus isolates in milk and the milking environment from small-scale dairy farms of São Paulo, Brazil, using pulsed-field gel electrophoresis

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

Sol-gel synthesis of mesoporous CaCu3Ti4O12 thin films and their gas sensing response

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Use of Pyrosequencing and Denaturing Gradient Gel Electrophoresis to Examine the Effects of Probiotics and Essential Oil Blends on Digestive Microflora in Broilers Under Mixed Eimeria Infection

A protective digestive microflora helps prevent and reduce broiler infection and colonization by enteropathogens. In the current experiment, broilers fed diets supplemented with probiotics and essential oil (EO) blends were infected with a standard mixed Eimeria spp. to determine effects of performance enhancers on ileal and cecal microbial communities (MCs). Eight treatment groups included four controls (uninfected-unmedicated [UU], unmedicated-infected, the antibiotic BMD plus the ionophore Coban as positive control, and the ionophore as negative control), and four treatments (probiotics BC-30 and Calsporin; and EO, Crina Poultry Plus, and Crina PoultryAF). Day-old broilers were raised to 14 days in floor pens on used litter and then were moved to Petersime batteries and inoculated at 15 days with mixed Eimeria spp. Ileal and cecal samples were collected at 14 days and 7 days postinfection. Digesta DNA was subjected to pyrosequencing for sequencing of individual cecal bacteria and denaturing gradient gel electrophoresis (DGGE) for determination of changes in ileal and cecal MC according to percentage similarity coefficient (%SC). Pyrosequencing is very sensitive detecting shifts in individual bacterial sequences, whereas DGGE is able to detect gross shifts in entire MC. These combined techniques offer versatility toward identifying feed additive and mild Eimeria infection modulation of broiler MC. Pyrosequencing detected 147 bacterial species sequences. Additionally, pyrosequencing revealed the presence of relatively low levels of the potential human enteropathogens Campylobacter sp. and four Shigella spp. as well as the potential poultry pathogen Clostridiun perfringens. Pre- and postinfection changes in ileal (56%SC) and cecal (78.5%SC) DGGE profiles resulted from the coccidia infection and with increased broiler age. Probiotics and EO changed MC from those seen in UU ilea and ceca. Results potentially reflect the performance enhancement above expectations in comparison to broilers not given the probiotics or the specific EO blends as feed supplements.