MINIMIZING COSOLVENT REQUIREMENTS FOR MICROEMULSION FORMED WITH BINARY SURFACTANT MIXTURES

The role of alcohols in microemulsion formation is primarily two-fold. They function as cosolvents by modifying surfactant partitioning between the aqueous and oleic phases and they function as cosurfactants stabilizing microemulsion to the exclusion of unbounaed structures such as liquid crystals, gels or precipitates. Given the freedom of choice among surfactants and their mixtures, the former role of the alcohol can easily be obviated. However, the latter requirement is more fundamental and not so easily removed. This study provides guidance in the purposeful construction of mixtures of synthetic surfactants which can minimize or eliminate alcohol requirements, depending on temperature and salinity. The approach Involves mixing straight tailed (high solubilization parameter) species with mid-chain branched (low cosolvent requirement) species in a spectrum of mole ratios and identifying the minimum alcohol concentration for stable microemulsion. A number of acceptable systems were found.     

Sandwich pairs in critical point theory

Since the development of the calculus of variations there has been interest in finding critical points of functionals. This was intensified by the fact that for many equations arising in practice the solutions are critical points of functionals. If a functional is semibounded, one can find a Palais-Smale (PS) sequence

These sequences produce critical points if they have convergent subsequences (i.e., if satisfies the PS condition). However, there is no clear method of finding critical points of functionals which are not semibounded. The concept of linking was developed to produce Palais-Smale (PS) sequences for functionals that separate linking sets. In the present paper we discuss the situation in which one cannot find linking sets that separate the functional. We introduce a new class of subsets that accomplishes the same results under weaker conditions. We then provide criteria for determining such subsets. Examples and applications are given.

     

Use of LIBS for rapid characterization of parchment

Parchment from different sources has been analyzed by laser-induced breakdown spectroscopy (LIBS) for determination of Ca, Na, K, Mg, Fe, Cu, and Mn. The LIBS results were compared with results from inductively coupled plasma spectroscopy (ICP) and good correlation was obtained. Rapid distinction between modern and historical samples was achieved by discriminant analysis of the LIBS data. Animal type recognition was also possible on the basis of Mg/Cu emission peak ratio and Mg depth profiling.     

New Laser Multiphoton Ionization Methods for Environmental Analysis

We report first attempts of applying laser multiphoton ionization to analysis of trace pollutants in environmental samples, including soils, aerosols and ambient air. A fast conductivity technique was developed for such on-line analysis and was applied to several (organic and inorganic) environmental samples. Matrix effects were investigated and compensation methods were suggested. Limits of detection in the ppb range are reported for polycyclic aromatic hydrocarbons (PAH) compounds.