Celso Valentim Santilli

Microstructure and corrosion resistance of inorganic-organic (ZrO2-PMMA) hybrid coating on stainless steel

Abstract Zirconia–polymethylmetacrylate hybrids prepared by a sol–gel method were deposited by dip-coating on stainless steel to improve the resistance against wet corrosion. The effect of the concentration of polymethylmetacrylate and the number of coating applications on the microstructure and corrosion performance of coated samples was investigated. The microstructural properties of samples was analyzed by scanning electron and atomic force microscopy, adhesion tests and profilemeter measurements. The electrochemical corrosion was evaluated through potentiodynamic polarization curves at room temperature. Results show that the sample prepared with 17 vol.% of polymethylmethacrylate has a maximum corrosion resistance, smaller roughness, are hermetic and adherent to the substrate. This film increases the life time of the stainless steel by a factor 30.

Study of Hybrid Silica-Polyethyleneglycol Xerogels by Eu3+ Luminescence Spectroscopy

Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.

Formation of SnO2 gels from dispersed sols in aqueous colloidal solutions

Abstract Transparent SnO2 gels were obtained from SnCl4 aqueous solution. The sol formation from tin oxihydroxy peptization in different concentrations and by electrolyte addition in solution was measured. It was verified that the residual presence of chloride ions compromises the colloidal system stability. The sol-gel transition was investigated as a function of the quantity of solid particles in the aqueous environment and of aging time at 60°C by infrared spectroscopy and rheological measurements. The transition from plastic to pseudoplastic flow observed with the increase in loading suggests that a continuous and three-dimensional network formation is closely related to hydrogen bridges and/or hydrogen clusters, culminating in the gel formation.

Structural electrical and optical properties of undoped and indium doped ZnO thin films prepared by the pyrosol process at different temperatures

Abstract The influence of the substrate temperature on the structural features and opto-electrical properties of undoped and indium-doped ZnO thin films deposited by pyrosol process was investigated. The addition of indium induces a drastic decrease (by a factor ≈10 10 for samples deposited at 300 °C) in the electrical resistivity of films, the lowest electrical resistivity (6 mΩ-cm) being observed for the film deposited at 450 °C. Films are highly transparent (>80%) in the Vis-NIR ranges, and the optical band gap exhibits a blue shift (from 3.29 to 3.33 eV) for the In-doped films deposited at increasing temperature. Preferential orientation of the ZnO crystallites with the c -axis perpendicular to the substrate surface and an anisotropic morphology of the nanoporous structure was observed for films growth at 300 and 350 °C.

Optical characteristics of Er3+-Yb3+ doped SnO2 xerogels

Abstract Er 3+ doped SnO 2 xerogels have been obtained from aqueous colloidal suspensions. Emission and excitation spectra were obtained and allowed the identification of two main families of sites for Er 3+ . In the first one Er 3+ substitutes for Sn 4+ in the SnO 2 cassiterite structure. In the second Er 3+ are found adsorbed at the SnO 2 particle surface. For the first family of sites the technological important infrared Er 3+ emission about 1.5 μm is efficiently excited through absorption at the SnO 2 conduction band at 3.8 eV. On the other hand the emission due to adsorbed ions appears inhomogeneously broadened by the statistical distribution of sites available for Er 3+ ions at the surface of the particles. Moreover it is not excited by the host. The emission of this second family of sites could be also excited by an energy transfer mechanism involving Yb 3+ ions also adsorbed a posteriori at particles surface. Results are compared with spectra obtained for Eu 3+ doped samples.

SAXS study of the kinetics of formation of ZnO colloidal suspensions

We have investigated, by in situ small-angle X-ray scattering (SAXS), the kinetics of formation of zinc oxide colloidal suspensions obtained after refluxing alcoholic solution of zinc acetate and catalysed by lithium hydroxide. The experimental results demonstrate that the suspensions are composed of colloidal spheroidal particles with a multimodal size distribution. The average radius of the main mode, approximately 2 nm, is invariant but the number of these basic particles continuously increases for increasing hydrolysis reaction time. The other two modes correspond to particles with average radii close to 6 and 10 nm, respectively. The larger particles are formed by coagulation of the smaller ones.

Crystal growth of Ce-doped and undoped LiCaAlF6 by the Czochralski technique under CF4 atmosphere

Ce-doped and undoped LiCaAlF6 (LiCAF) single crystals 50 mm in diameter were grown by the Czochralski technique. The formation of inclusions and cracks accompanying the crystal growth was investigated. The dependence of lattice parameters on the temperature was measured for LiCAFand LiSrAlF 6 single crystals. Linear thermal expansion coefficients for both these crystals were evaluated. Higher transmission properties for LiCAFsingle crystals were achieved in the UV and VUV wavelength regions. # 2001 Elsevier Science B.V. All rights reserved.

Immobilization of streptavidin in sol–gel films: Application on the diagnosis of hepatitis C virus

Recent advances have accelerated the development of biosensors for the analysis of specific gene sequences. In this kind of biosensor, a DNA probe is immobilized on a transducer and the hybridization with the target DNA is monitored by suitable methodology. In the present work, the streptavidin (STA) was encapsulated in thin films siloxane-poly(propylene oxide) hybrids prepared by sol-gel method and deposited on the graphite electrode surface by dip-coating process. Biotinylated 18-mer probes were immobilized through STA and a novel amperometric DNA biosensor for the detection and genotyping of the hepatitis C virus (genotypes 1, 2A/C, 2B and 3) is described. The HCV RNA from serum was submitted to reverse transcriptase-linked polymerase chain reaction (RT-PCR) and biotin-labeled cDNA was obtained. Thus, the cDNA was hybridized to the target-specific oligonucleotide probe immobilized on the graphite electrode surface and following the avidin-peroxidase conjugate was added. The enzymatic response was investigated by constant potential amperometry at -0.45V versus Ag/AgCl using H(2)O(2) and KI solutions. HCV RNA negative and positive controls and positive samples of sera patients were analyzed and the results were compared to commercial kit. The proposed methodology appeared to be suitable and convenient tool for streptavidin immobilization and diagnose of HCV disease.

Controlled Cisplatin Delivery from Ureasil−PEO1900 Hybrid Matrix

The ability of assembling inorganic, organic, and even bioactive components in a single material unfolds an exciting direction in the development of novel multifunctional hybrid materials. Recently, we have observed that the hydrophilic/hydrophobic character of the organic polymeric moieties determines the swelling/diffusion control of the drug release. In this work, the antitumor cisplatin (CisPt) molecules incorporated into the ureasil-PEO (poly(ethylene oxide)) hybrid material was used as a probe for the in situ and simultaneous UV-vis and Raman spectroscopies monitoring of the kinetics of both the water uptake as well as the CisPt release by the hybrid matrix. Drug molecules were incorporated during the hydrolysis and polycondensation steps. The monolithic xerogel were analyzed by X-ray absorption spectroscopy and differential scanning calorimetry, while the drug release properties were monitored by Raman as well as UV-vis spectroscopies. The results show that the molecular structure of the CisPt is preserved in the one pot sol-gel route used in synthesizing the CisPt-loaded PEO1900 hybrid. The in situ monitoring of water uptake clearly points out the key contribution of the osmotic flow on the stepped profile of the CisPt delivered from the PEO1900 hybrid matrix.

Structural changes of biocompatible neutral microemulsions stabilized by mixed surfactant containing soya phosphatidylcholine and their relationship with doxorubicin release.

Depending on the composition, the mixture of surfactant, oil and water, may form supramolecular aggregates with different structures which can significantly influence the drug release. In this work several microemulsion (ME) systems containing soya phosphatidylcholine (SPC) and eumulgin HRE40 (EU) as surfactant, cholesterol (O) as oil phase, and ultra-pure water as an aqueous phase were studied. MEs with and without the antitumoral drug doxorubicin (DOX) were prepared. The microstructures of the systems were characterized by photon correlation spectroscopy, rheological behavior, polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). The results reveal that the diameter of the oil droplets was dependent on the surfactant (S) amount added to formulations. The apparent viscosity was dependent on the O/S ratio. High O/S ratio leads to the crystallization of cholesterol polymorphs phases which restricts the mobility of the DOX molecules into the ME structure. Droplets with short-range spatial correlation were formed from the ME with the low O/S ratio. The increase of the cholesterol fraction in the O/S mixture leads to the formation of ordered structures with lamellar arrangements. These different structural organizations directly influenced the drug release profiles. The in vitro release assay showed that the increase of the O/S ratio in the formulations inhibited the constant rate of DOX release. Since the DOX release ratio was directly dependent on the ratio of O/S following an exponential decay profile, this feature can be used to control the DOX release from the ME formulations.