THE EFFECT OF SOLVENT POLARITY ON THE CONDENSATION OF HYDROLYZED TETRAETHYLORTHOSILICATE IN MICROEMULSION GELS

A study of the condensation of hydrolyzed tertaethylorthosilicate (TEOS) was conducted to investigate the influence of solvent polarity. A non-aqueous microemulsion was formed to which was added water (pH 1) and TEOS. The various condensation products were observed with ²9Si NMR of systems of differing amounts of formamide and decanol/decane at increasing time intervals. The solvent polarity of the solvent system was found to clearly influence the initial and final rates of condensation, despite the fact that the specific condensed moieties were the same in each of the systems studied.     

Some Fundamentals of the One-Step Formation of Double Emulsions

The recently introduced one-step process to form double emulsions is analyzed using generalized phase diagrams of water, ethylene oxide adduct surfactants, and hydrocarbons. With the process used, we found three factors to be involved in the successful formation of double emulsions. Temporary ultra-low interfacial tension allowed drops of irregular shape to exist, a large part of the emulsion formed a bicontinuous microemulsion at intermediate times, and the interfacial tension was temporarily reduced extremely by significant amounts of all three compounds transferred over the interfaces in different directions depending on the stage of the process.     

Sun Screen Microemulsions

Three sunscreen compounds, p-amino benzoic acid (PABA), octyl-di-methyl-p-amino benzoic acid (ODP), and 2-hydroxy-4-methyoxy-5-sulfobenzophenone (HMSB) were incorporated into a model microemulsion system stabilized by sodium dodecyl sulfate and pentanol.

The PABA acted as a hydrotrope supporting the stability of an oil-in-water microemulsion, while ODP had the opposite effect. HMSB, finally retained both the oil-in-water and the water-in-oil parts of the microemulsion system.     

ALFRED LOTTERMOSER -A Pioneer in the Application of Colloid Chemistry

These words by one of Lottermoser's collaborators are of a kind usually reserved for the truly great scientists. Alfred Lottermoser's scientific contributions and his leadership in developing the Institute for Colloid Chemistry at the Technical University in Dresden, Germany, without significant state support and during a time, 1922, when runaway inflation made such support worthless, are each sufficient for his name to remain important in the history of colloid chemistry. Together, they guarantee a place among the true greats.     

Role of liquid crystal in the emulsification of a gel emulsion with high internal phase fraction

A gel emulsion with high internal oil phase volume fraction was formed via an inversion process induced by a water–oil ratio change. The process involved the formation of intermediate multiple emulsions prior to inversion. The multiple emulsions contain a liquid crystal formed by the surfactant with water; this was both predicted by the equilibrium phase diagram as well as observed using polarization microscopy. These multiple emulsions were more stable compared to alternative multiple emulsions prepared in the same way with a surfactant that does not form liquid crystals. While the formation of a stable intermediate multiple emulsion may not be a necessary condition for the inversion to occur, the transitional presence of a liquid crystal proved to be a significant factor in the stabilization of the intermediate multiple emulsions. The resulting gel emulsion contained a small fraction of the liquid crystal according to the phase diagram, and it exhibited excellent stability.     

Silicon NMR Spectra from the Reaction Species Between Tetraethoxysilane and Calcium Nitrate Hydrate

NMR spectra were recorded of the silicon species obtained in the reaction between tetraethoxysilane and calcium nitrate hydrate in ethanol.

The tetraethoxysilane reacted with a maximum of three of the four waters of hydration of the calcium nitrate at room temperature within a few days. The fourth water reacted after extended times (33 days) at room temperature or at enhanced temperature (60°C) within 24 hours. Samples with less than sufficient water for a complete reaction showed the corresponding amount of unreacted tetraethoxysilane.

The calcium nitrate stayed colloidally dispersed within the ethanol silica gel and remained so even after the ethanol was removed.     

Efficiency enhancement in a microcavity solid-state dye laser with Bragg grating reflectors

Bragg grating reflectors placed along microcavity facets can improve the efficiency of a polymer dye laser built with such a microcavity. The impact of different reflector designs on the mode pattern and resonance frequencies of the microcavity is numerically simulated and analyzed. This rigorous physical model is based on solving the Maxwell equations and includes such material properties as absorption, dispersion, fluorescence and optical gain. In certain cases, an asymmetrical layout of the reflectors can be more preferable than the pair of reflectors located on opposite sides of the microcavity as it is implemented for typical design.