Adriana A. Silva

Electrorheological and dielectric behavior of new ionic liquid/silica systems

New phosphonium-based ionic liquids, denoted, 11-carboxyundecyltriphenylphosphonium bromide (IL1) and octadecyltriphenylphosphonium iodide (IL2), were employed on the sol-gel synthesis to prepare new silica-based matrices. The fastest gelation during the sol-gel process was observed in hydrolysis/condensation of tetraethoxysilane in the presence of IL1. The confinement of ionic liquids (especially IL1) inside the silica networks was suggested by thermogravimetric analysis and Fourier transform infrared spectroscopy. The resulting ionogels present higher permittivity than pure silica and were used as the solid component for the development of new electrorheological fluids, presenting good ER behavior, mainly those prepared with IL1.

Characterization of nanostructured epoxy networks modified with isocyanate-terminated liquid polybutadiene

Polybutadiene-block-epoxy prepolymer (DGEBA-b-PBNCO) copolymers with multi-branched topological structure were prepared by reacting isocyanate-multifunctionalized liquid polybutadiene (PBNCO) with DGEBA prepolymer and used to develop nanostructured rubber-modified epoxy thermosets cured with triethylene-tetramine (TETA) as the aliphatic amine. The nanoscopic structure was obtained with the addition of as high as 20 phr of rubber component and successfully demonstrated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The glass transition temperature of the rubber-modified epoxy networks was slightly higher than the neat epoxy system. In addition, a unique combination of outstanding toughness and increased modulus and T(g) was achieved in these modified systems, which was attributed to the peculiar morphology associated with a strong interfacial adhesion imparted by the reaction between the isocyanate and hydroxyl groups present in the PBNCO and epoxy resin, respectively. The effect of the PBNCO on the gelation time of the epoxy/TETA system was investigated by rheological techniques. The NCO-functionalized polybutadiene decreased the gelation time, indicating an accelerating effect on the curing process, probably because of the urethane groups formed by the reaction between PBNCO and the epoxy resin during the PB-b-ER block copolymer preparation.

Nanostructured thermosets from ionic liquid building block–epoxy prepolymer mixtures

Ionic liquids based on trihexyl(tetradecyl)phosphonium combined with dicyanamide counteranion were used for the first time as functional additives to achieve epoxy networked polymeric materials which display a structuration at nanoscale (20–30 nm) with dramatic mechanical properties and a higher thermal stability (>400 °C). In fact, the curing process was studied by FTIR, DSC highlighting an increase of the conversion epoxide groups in function of the IL amount (5–30 phr) and the morphology has been revealed by transmission electronic microscopy (TEM) and atomic force microscopy (AFM).

Silica prepared in the presence of alkylphosphonium-based ionic liquids and its performance in electrorheological fluids

This work highlights the effect of silica particles prepared by a sol–gel process in the presence of different phosphonium-based ionic liquids on the electrorheological behavior of the corresponding suspension in silicone oil. The silica particles were prepared by hydrolysis/condensation of tetraetoxy silane (TEOS) in basic medium and in the presence of three different commercial ionic liquids: tri-isobutyl(methyl)phosphoniumtosylate (IL106), tri(n-butyl)(tetradecyl)phosphonium-dodecylbenzene-sulfonate (IL201) and trihexyl-(tetradecyl)-phosphonium-bis-2,4,4-(trimethylpentyl)-phosphinate (IL104). The resulting material was characterized by Fourier-transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and dielectric properties. The confinement of the ionic liquids inside the silica particles was suggested by thermogravimetric analysis. The presence of ILs also exerts a strong influence on the morphology and imparts good polarization ability to the silica. The electro-rheological response of the corresponding ionogel suspensions in silicone oil was investigated. A significant ER effect was observed for the fluid containing silica prepared in the presence of IL106. In fact, a very good response under the action of an electrical field corresponding to 3 kV mm−1 was achieved, with a shear stress value as high as 1215 Pa. This behavior may be attributed to the presence of the IL confined in the silica particles and also to the peculiar morphology which favors the formation of a columnar structure to a high extent.

Verdete de cedro do abaeté como fonte de potássio: caracterização, tratamento térmico e reação com CaO

The potassium is one of the most important macronutrients to the soil. However, in the Brazilian soils this nutrient becomes scarce due to the high acidity of tropical soils. Thus, the demand for alternative sources of potassium grows considerably. In this context, we performed a chemical and mineralogical characterization of a verdete from Cedro do Abaete, Minas Gerais, as well as an evaluation of the verdete thermal treatment, with or without addition of calcium oxide (CaO), in order to solubilize the potassium present in the rock. The characterization of this rock was developed by the techniques of X-ray diffraction (XRD), X-ray fluorescence (XRF) and infrared spectroscopy (IR). The evaluation of the XRF results showed that the rock has 6,95 mass% of K2O, related to the presence of glauconite. This was confirmed by the XRD due to the presence of characteristics peaks at 1.0, 0.45, 0.24 e 0.15 nm and the occurrence of IR bands at 3520, 3440, 1020 and 630 cm-1. There is also a high content of SiO2 (64,65%), indicative of the presence of quartz, which is characterized by an intense peak at 0.335 nm. During the thermal treatment, the verdete was heated for 2 hours at a temperature of 1200 oC. In order to increase the solubility of potassium present in the rock, reactions were carried out with CaO in proportions of 10, 20 and 30% by weight. The structural changes in the rock were followed by XRD and IR. The changes in the position of the characteristic bands of Si-O, in the IR spectra at around 1100 cm-1, and the disappearance of X-ray diffraction peaks, related to glauconite, confirmed the reaction between the rock and the CaO. The reaction with 20% of CaO allowed an extraction of 7.7 % of the potassium present in the sample.

Modeling controlled potassium release from phlogopite in solution: exploring the viability of using crushed phlogopitite rock as an alternative potassium source in Brazilian soil

The chemical and mineralogical properties of phlogopitite, a rock containing the mineral phlogopite, were studied aiming at employment as an alternative source of potassium. Mineralogical characterization of this rock was performed using X-ray diffractometry, X-ray fluorescence, scanning electron microscopy and infrared spectroscopy. According to the results, phlogopite contains approximately 82.6 g K2O kg-1 (ca. 9%). The kinetics involved in the release of the potassium ions from the mineral were examined using acidic solutions (nitric, citric, oxalic and Mehlich-1) and a salt solution (sodium tetraphenylboron, Na[B(C6H5)4]). The experimental results from the kinetic studies were used to determine the mathematical relationship between the concentration of potassium released and the reaction time.

Effect of sonication and clay content on the properties of unsaturated polyester/montmorillonite nanocomposites

The aim of this work is to evaluate the effect of sonication and clay content on the crosslinking and curing characteristics and the final properties of unsaturated polyester/montmorillonite nanocomposites. The Cloisite 30B clay (1, 3 or 5 wt.%) was dispersed in the resin by mechanical stirring and sonication at different ultrasonic amplitudes (20% and 30%). Amplitude is one of the most important parameter when reproducing sonication results. An increase in viscosity with clay incorporation, at 20% amplitude, was related to the better dispersion, corroborating differential scanning calorimetry results. The sequential diffractograms confirmed the influence of the clay on resin crosslinking and the curing process. An intercalated structure was observed for samples up to 3 wt.% of clay and an amplitude of 20% during sonication, corroborating the increase in flexural strength and lower values of coefficient of thermal expansion. Modulus increased with the incorporation of clay, whereas impact strength and linear burning rate declined.