Small-angle X-ray scattering study of sol-gel-derived siloxane-PEG and siloxane-PPG hybrid materials

Hybrid organic-inorganic two-phase nanocomposites of siloxane-poly(ethylene glycol) (SiO3/2-PEG) and siloxane-poly(propylene glycol) (SiO3/2-PPG) have been obtained by the sol-gel process. In these composites, nanometric siloxane heterogeneities are embedded in a polymeric matrix with covalent bonds in the interfaces. The structure of these materials was investigated in samples with different molecular weights of the polymer using the smalt-angle X-ray scattering (SAXS) technique. The SAXS spectra exhibit a well-defined peak that was attributed to the existence of a strong spatial correlation of siloxane clusters. LiClO4-doped siloxane-PEG and siloxane-PPG hybrids, which exhibit good ionic conduction properties, have also been studied as a function of the lithium concentration [O]/[Li], O being the oxygens of ether type. SAXS results allowed us to establish a structural model for these materials for different basic compositions and a varying [Li] content. The conclusion is consistent with that deduced from ionic conductivity measurements that exhibit a maximum for [O]/[Li] =15.

Thermal degradation of geomembranes after exposure to heat

HDPE and PVC geomembranes are sensitive to changes in their properties when in contact with high temperatures. The effects of hot temperature on polymeric geomembranes are assessed by the ASTM D794 and ASTM D5721.This paper brings an analysis of degradation of the Poly Vinyl Chloride (PVC) and High Density Poly Ethylene (HDPE) geomembranes when exposed to conventional and air oven after specific periods.. Mechanical and physical properties were evaluated. OIT tests were also performanced to evaluate the level of oxidation degradation occurred on the HDPE geomembranes. Geomembranes of two thicknesses were tested: 1.0, 2.0 nun (PVC) and 0.8, 2.5 mm, (HDPE). The results obtained show, for example, that after the last period of exposure, the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to heat presented increases in deformation. OIT tests showed efficient to detect some level of degradation on the HDPE geomembranes.

Kinetic parameters of polymer degradation by SAPO-37

High density poly(ethylene) has been submitted to thermal degradation alone, and in the presence of silicoaluminophosphate SAPO-37. The processes were carried out in a reactor connected on line to a gas chromatograph/mass spectrometer in order to analyze the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature until 800 degreesC, under nitrogen dynamic atmosphere, with multiple heating rates. From TG curves, the activation energy related to degradation process was calculated using the Flynn and Wall multiple heating rate kinetic model for pure polymer (PE) and for polymer in the presence of catalyst (PE/S37). SAPO-37 showed good selectivity for low molecular mass hydrocarbons in PE catalytic degradation.

Controlled Cisplatin Delivery from Ureasil-PEO1900 Hybrid Matrix

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Micropatterned nanocomposite hydrogels for biosensing applications

This paper describes the use of Au nanoparticle (NP)-containing hydrogel microstructures in the development of electrochemical enzyme-based biosensors. To fabricate biosensors, AuNPs were conjugated with glucose oxidase (GOX) or horseradish peroxidase (HRP) molecules and were dispersed in the prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA). Vinylferrocene (VF) was also added into the prepolymer solution in order to lower operating potential of the biosensor and to prevent oxidation of interfering substances. The prepolymer solution was photolithographically patterned in alignment with an array of Au electrodes fabricated on glass. As a result, electrode arrays became functionalized with AuNP/GOX- or AuNP/HRP-carrying hydrogel microstructures. Performance of the biosensors was characterized by impedance spectroscopy, chronoapmerometry and cyclic voltammetry. Impedance measurements revealed that inclusion of Au nanoparticles improved conductivity of PEG hydrogel by a factor of 5. Importantly, biosensors based on AuNP-GOX complex exhibited high sensitivity to glucose (100μAmM -1cm -2) in the linear range from 0.1 to 10mM. The detection limit was estimated to be 3.7×10- 7M at a signal-to-noise ratio of 3. Biosensors with immobilized AuNP/HPR had a linear response from 0.5 to 5.0μM of hydrogen peroxide with sensitivity of 1.4mAmM -1cm -2. The method for fabricating nanoparticle-carrying hydrogel microstructures described in this paper should be widely applicable in the development of robust and sensitive electrochemical biosensors. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Use of hemoglobin as alternative to peroxidases in cholesterol amperometric biosensors

Sophisticated molecular architectures can be produced with the layer-by-layer (LbL) method, which may combine distinct materials on the same film. In this study, we take advantage of this capability to produce cholesterol amperometric biosensors from LbL films containing hemoglobin (Hb) and cholesterol oxidase in addition to the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(ethylene imine) (PEI). Following an optimization procedure, we found that an LbL film deposited onto ITO substrates, with the architecture ITO(PEI/Hb)5(PEI/COx)10, yielded a sensitivity of 93.4 μA μmol L-1 cm-2 for cholesterol incorporated into phospholipid liposomes, comparable to state-of-the-art biosensors. Hb acted as efficient electron mediator and did not suffer interference from phospholipids. Significantly, cholesterol could also be detected in real samples from chicken egg yolk, with no effects from potential interferents, including phospholipids. Taken together these results demonstrate the possible fabrication of low cost, easy-to-use cholesterol amperometric biosensors, whose sensitivity can be enhanced by further optimizing the molecular architectures of the LbL films. © 2012 Elsevier B.V.

Synthesis of PTSH-modified CeO2 nanoparticles: Effect of the modifier on structure, optical properties, and dispersibility

CeO2 nanoparticles were synthesized by the precipitation method and modified with para-toluene sulfonic acid (PTSH), either in situ or post-synthesis. The presence of PTSH in the samples was confirmed by FTIR. PXRD and FTIR analyses showed that the post-synthesis PTSH modification altered the CeO2 structure, whereas the in situ modification maintained intact the crystalline structure and UV-vis absorbance properties. For both in situ and post-synthesis modifications, TEM images revealed the presence of nanoparticles that were 5nm in size. The dispersibility of the in situ PTSH-modified material in a hydrophilic ureasil-poly(ethylene oxide) matrix was investigated using SAXS measurements, which indicated that CeO2 nanoparticles modified with PTSH in situ were less aggregated within the matrix, compared to unmodified CeO2 nanoparticles. © 2013 Elsevier B.V.

Structural characteristics of P123-modified supercritical drying and hydrophobic ambient pressure drying aerogels

Supercritical drying (SCD) and hydrophobic ambient pressure drying (APD) aerogels were prepared from hydrolysis of tetraethoxysilane in solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123) in the range of composition below the threshold for the ordered mesoporous silica precipitation. APD was carried out after silylation of wet gels with trimethylchlorosilane (TMCS) or hexamethyldisilazane (HMDZ). The samples were analyzed by small-angle X-ray scattering and nitrogen adsorption. Wet gels are formed by mass-fractal domains, with fractal dimension close to 2, and larger pores superposing the pores belonging to the fractal structure in case of high P123 concentrations. Aerogels exhibit smaller-sized mass-fractal domains with larger mass-fractal dimension accounting for some porosity elimination on drying. The pore volume of the aerogels increases significantly with the P123 amount and it is even larger in the APD aerogels than in the SCD aerogels. © 2013 Elsevier B.V. All rights reserved.

Avaliação histopatológica em tecido conjuntivo subcutâneo de ratos de um cimento de ionômero de vidro experimental para forramento cavitário

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação e caracterização de sílicas mesoporosas

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

Calcinação e estabilidade térmica de Sílicas mesoporoas preparadas com Pluronic P123

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

Utilização de uma matriz híbrida orgânica-inorgânica na dinâmica de liberação controlada de fármacos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese, caracterização e estudo físico-químico de nanopartículas formadas pela interação de derivados hidrofílicos de quitosana com DNA

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Simulação de poli(etileno glicol) em água por dinâmica molecular

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Síntese, caracterização e estudos em solução de terpolímeros antififílicos termo-sensíveis ao pH: uma perspectiva para obtenção de sistemas transportadores de fármacos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)