Jéssica Alves Marins

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.

Flexible magnetic membranes based on bacterial cellulose and its evaluation as electromagnetic interference shielding material.

Flexible magnetic membranes with high proportion of magnetite were successfully prepared by previous impregnation of the never dried bacterial cellulose pellicles with ferric chloride followed by reduction with sodium bisulfite and alkaline treatment for magnetite precipitation. Membranes were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating magnetometer, field emission scanning electron microscopy (FEG-SEM) and impedance spectroscopy. Microwave properties of these membranes were investigated in the X-band (8.2 to 12.4 GHz). FEG-SEM micrographs show an effective coverage of the BC nanofibers by Fe3O4 nanoparticles. Membranes with up to 75% in weight of particles have been prepared after 60 min of reaction. Magnetite nanoparticles in the form of aggregates well adhered to the BC fibers were observed by SEM. The average crystal sizes of the magnetic particles were in the range of 10±1 to 13±1 nm (estimated by XRD). The magnetic particles in the BC pellicles presented superparamagnetic behavior with a saturation magnetization in the range of 60 emu g(-1) and coercive force around 15 Oe. These magnetic pellicles also displayed high electrical permittivity and a potential application as microwave absorber materials.

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.

New electrorheological fluid obtained from mercaptosilsesquioxane-modified silicate suspensions.

Ormosil based on mercaptosilsesquioxane-modified silicate (SiO2/SSQ-SH) particle was prepared by sol-gel process involving a co-condensation of the hydrolyzed 3-mercaptopropyl-trimethoxysilane (MPTMS) and tetraetoxysilane (TEOS). The resulting material was characterized by (29)Si solid nuclear magnetic resonance spectroscopy ((29)Si NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FEG-SEM) and small angle X-ray scattering (SAXS). The (SiO2/SSQ-SH) particle presents a hierarchical structure, extending from micro to nanoscale and consisting of three structural levels. This SiO2/SSQ-SH particle was used for the first time as the dispersed phase in silicone oil suspension to develop a new electro-rheological fluid with a very good response under the action of electrical field from 1 to 4 kV/mm, whose values are comparable to those exhibited by other conventional ER fluids, under the influence of electric field.