GSU View, 2010-01-28

Newsletter published by Governors State University 2007-current

СОЗДАНИЕ ВЫСОКОВОЛЬТНЫХ ИМПУЛЬСНЫХ КОНДЕНСАТОРОВ НА ОСНОВЕ КОМБИНИРОВАННОГО ПЛЕНОЧНОГО ДИЭЛЕКТРИКА

Research into feasibility of designing high-voltage pulse capacitors based on composite film dielectric systems is presented.Рассматриваются результаты исследований по созданию высоковольтных импульсных конденсаторов на основе комбинированных пленочных диэлектрических систем.Розглядаються результати досліджень зі створення високовольтних імпульсних конденсаторів на основі комбінованих плівкових діелектричних систем

Textural characteristics and organization of composites with fumed silicas and high-molecular weight compounds

Various composites with nanosilicas, as well as with other nanooxides, and polymers are of importance from a practical point of view. Detailed textural and morphological characterization, applied here to nanosilicas treated alone and in composites with a set of polymers (poly(vinyl pyrrolidone), poly(vinyl alcohol), poly(ethylene oxide), poly(ethylene glycol), polydimethylsiloxane, and polymethylsiloxane) and proteins (egg albumin, gelatin, and ossein), could be considered as a tool to evaluate the reorganization of hierarchical structures in composites from aggregates of nanoparticles, agglomerates of aggregates, to micro and visible particles. This analysis allows one to elucidate various changes in the porosity, accessible surface area, contributions of pores of different sizes and shapes and pore walls with silica or polymer/protein depending on a set of varied factors. Collected information could be used to forecast possible characteristics and properties of various composites with nanooxides. Among the factors affecting the properties and characteristics of the composites, a type, molecular weight, and content of a polymer and treatment conditions may play an important role. The presence of a large set of the factors makes difficult analysis of the composites using simplified approaches and methods. As a whole, selection of the composition and certain conditions of the composite preparation allows one to control all the textural characteristics of the final materials. For these purposes, the characteristics should be accurately estimated with minimum possible errors using well developed and adequate methods.</jats:p

Confined space effects on various liquids interacting with fumed nanooxides and porous silicas

Interfacial phenomena at a surface of porous and highly disperse adsorbents in the systems containing strongly and weakly bound and unbound liquids depend strongly on the confined space effects. These effects as well as the temperature behavior of liquids located in pores or voids between nanoparticles depend on many factors. They are the pore size distributions, pore volume, specific surface area, surface chemistry of adsorbents, chemical structure and molecular sizes of adsorbates, accessibility of pores vs. probe molecule sizes, as well as textural instability of adsorbents. This instability can appear, e.g., as compaction of fumed oxides under action of liquid adsorbates, especially water, or due to mechanochemical activation. The aim of this study is to analyze features of the interfacial phenomena upon interactions of fumed oxides (silica, alumina, alumina/silica/titania) and porous silicas (silica gels and precipitated silica) with polar (water, dimethyl sulfoxide), weakly polar (chloroform), and nonpolar (n-decane, aromatic benzene and toluene) liquid adsorbates depending on the morphological and textural characteristics of the adsorbents, various adsorbate characteristics, and temperature. The observed effects as well as related phenomena are important because they can differently influence the efficiency of practical applications of adsorbents under various conditions (temperature, pressure, concentrations) depending on the characteristics of adsorbents and adsorbates (liquids, solvents and solutes).</jats:p

Features of the morphology and texture of silica and carbon adsorbents

The morphological and textural characteristics of various silicas (93 fumed silicas and 56 porous silicas), different carbons (230), and porous polymers (53) are analyzed using probe (nitrogen, argon, benzene, n-decane, water) adsorption, small angle X-ray scattering (SAXS), and transition (TEM), scanning (SEM) electron and atom force (AFM) microscopies. There are certain correlations between pore volume (Vp) and specific surface area (SSA, SBET) for these materials. Synthesis and treatment temperatures affect this relationship since a linear Vp - SBET approximation scatter decreases with decreasing these temperatures. Silicas are composed of nonporous nanoparticles (NPNP), but activated carbons (AC) are composed of porous nanoparticles (PNP). For different materials, NP are weakly or strongly packed in secondary structures. However, there are general features of pore size distributions (PSD) for NP-based materials, e.g., minimal contribution of narrow mesopores of 3-5 nm in radius due NP-packing effects. For AC produced using the same chars and activation agents but with varied activation time, the textural characteristics demonstrate smooth changes with increasing burn-off degree: nanopores partially transform into narrow mesopores with opposite PSD shifts of broad mesopores and macropores. Comparison of adsorption (open pores accessible for probes) and SAXS (both open and closed pores) data for carbons shows that the difference decreases with increasing burn-off degree due to decreasing contribution of closed pores. Most clear pictures on the particulate morphology and texture could be obtained in parallel analysis using adsorption, SAXS, and microscopic methods with appropriate data treatments.</jats:p