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Preparação e caracterização de nanocompósitos de LDPE e LDPE/EVA com partículas de Ag/TIO2 para aplicações antimicrobiais
(Universidade Federal de São Carlos, 2009-10-02) Olyveira, Gabriel Molina de; Pessan, Luiz Antonio; https://lattes.cnpq.br/8276650236213537; https://lattes.cnpq.br/1681746201551274
This study investigated the use of a charger inorganic (titanium dioxide) as a support for silver nanoparticles and evaluated the use of material obtained as filler in polymer for antimicrobial application.Silver nanoparticles-titanium dioxide were synthesized by the reduction method developed by Turkevich, also known as a method of citrate. Therefore, we used three different types of titanium dioxide in the colloidal synthesis and found that nanometer titanium dioxide showed better results for the deposition of silver nanoparticles. Silver Nitrate was reduced by sodium citrate with and without the presence of a surfactant (PVP-Polyvinylpyrrolidone) resulting in a stable suspension of nanoparticles of silver / titanium dioxide. We also tested NH4OH (ammonium hydroxide) to prevent the growth of nanoparticles during the reaction. Nanocomposite of LDPE and LDPE / EVA were produced by mixing in the molten state with the Ag nanoparticles-titanium dioxide resulting from the colloidal synthesis. By assessing the rheological, thermal and morphological analysis we found that compared with nanocomposite LDPE / EVA, LDPE nanocomposite showed better results with regard to dispersion of the charges, but nanocomposite LDPE / EVA showed better results in antimicrobial assays due to the polar nature the grouping of EVA able to bind more easily to inorganic fillers.
Caracterização ótica não-linear em cerâmicas ferroelétricas transparentes (CFT s) de PLZT: TR (TR = nd,Ho, Er, Tm e Yb)
(Universidade Federal de São Carlos, 2009-10-02) Milton, Flávio Paulo; Garcia, Ducinei; https://lattes.cnpq.br/5236758856687873
Lead titanate zirconate modified with lanthanum, or PLZT, is one the most ferroelectric compounds utilized in electronic devices, due to its versatility and low production costs in comparison with single-crystalline materials. When adequately prepared, this system presents good optical (high optical transmission) properties, in the visible and near infrared range, and can be electro-optically characterized. Recently, in the end of 90 s, it was verified its high potential as host of photoluminescent ions, as the lanthanide (rare-earth) family. The possibility to use its electro-optic properties (due to its ferroelectric characteristics) and its photoluminescent properties (achieved by the doping process) together ,enlarges the range of application of this system. In this way, the electro-optical characterization of doped PLZT ceramics becomes essential, besides the photonic characterization. In this work, the Senarmont compensator method for electro-optical characterization, or dynamic method, was instrumented, and the values of the induced (due to the quadratic electrooptic effect, Kerr) and permanent (due to the linear electro-optic effect, Pockels) birefringence were determined as a function of the temperature, wave-length and electric-field frequency, of the rare-earth (Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3) doped PLZT, with La/Zr/Ti=9/65/35, ceramics. The results shown a relationship between of the electro-optic (electro-optic coefficients, or birefringence values) and the dielectric, ferroelectric and structural properties (studied in others works) of the ceramics, that were related with the site occupancy and the structural defects due to the aliovalent dopant. It also can be identified two distinct birefringence dependence as a function of the electric field, for the same electro-optic effect (Kerr, or Pockels), identified as a function of the doping process. In the case of electro-optical characterizations in function of the variable frequency, was observed an agreement with the characterization ferroelectric results made in other works in GCFerr, being evidenced the reduction of electro-optical properties with increasing frequency, where if it observed the occurrence of anomalies in the Pockels response with direct influence on the response Kerr. The characterization as a function of wavelength showed the occurrence of two types of behavior depending on the dopant ion used, being one of them the reduction of the values of birefringence with increasing wavelength (the samples pure and doped ions neodymium (Nd) and ytterbium (Yb)), with a tendency to expected behavior in the literature, however, in the second was seen irregular increase birefringence with increase wavelength (for samples doped with ions holmio ( Ho), erbium (Er) and thulium (Tm),not existing relation with to the theoretical models adopted. In relation the characterization as a function of temperature, this was carried through in a temperature interval that understood the characteristic temperatures of systems relaxores (freezing temperature (TF), the maximum dielectric permittivity (TM (e)) and Burns (TB)), except for the sample doped with neodymium ions, whose freezing temperature is below interval worked. By the curve of birefringence (Δn) as a function of temperature was possible to determine the temperature of maximum birefringence for each of the samples, correlated them with each other. Through the curve (d Δn / dt) vs. T was possible to identify a relationship between the maximum variations, positive and negative birefringence with the temperature characteristics TF and TB.