This paper presents an investigation of the effects of trace water on the charging of silica (SiO(2)) particles dispersed in a nonpolar medium. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and aggregation stability in such systems. One factor that is often overlooked in the preparation of nonpolar colloidal dispersions is the amount of water that is introduced to the system by hygroscopic particles and surfactants. The amount and location of this water can have significant effects on the electrical properties of these systems. For nonpolar surfactant solutions it has been shown that water can affect the conductivity, and it has been speculated that this is due to swelling of the polar cores of inverse micelles, increasing the fraction of them that are charged. Some studies have suggested that particle surface charging may also be sensitive to water content, but a clear mechanism for the process has not been fully developed. The situation with particles is further complicated by the fact that it is often unclear whether the water resides on the particle surfaces or in the polar cores of inverse micelles. The current work explores not only the effect of water content on reverse micelle and particle charging but seeks to differentiate between water bound to the particles and water located in the micelles. This is accomplished by measuring the solution conductivity and the electrophoretic mobility of silicon dioxide particles dispersed in solutions of Isopar-L and OLOA 11000. The water content is determined for both the dispersion and the supernatant after centrifuging the particles out. It is found that at equilibrium the majority of the water in the system adsorbs to the surface of the hygroscopic silica particles. In addition, the effect of water on particle electrophoretic mobility is found to be dependent on surfactant concentration. At small OLOA concentrations, additional water results in an increase in particle mobility due to increased particle charging. However, at large OLOA concentrations, additional water leads to a decrease in particle mobility, presumably as a result of increased electrostatic screening or neutralization. Thus, particle charging and electrophoretic mobility in an apolar surfactant solution are found to be highly sensitive to both the total water content in the system and to its concentration relative to the amount of surfactant present.

This paper examines the effects of temperature on the micellization and particle charging behavior of the Span surfactant series in an apolar environment. The critical micelle concentrations of each of six surfactants at five temperatures were measured by conductometric techniques. The thermodynamic properties of micellization were calculated using Gibbs-Helmholtz analysis. Magnesia particles were then dispersed in solutions of these surfactants, and their electrophoretic mobilities were measured at three temperatures. Preliminary small-angle neutron scattering (SANS) experiments were conducted to measure the size of aggregates (referred to as reverse micelles) of three of the surfactants. It was found that for all but one of the surfactants the critical micelle concentration (CMC) increased by as much as an order of magnitude across a 40 °C range of temperature. One of the surfactants exhibited a decrease in CMC upon increasing temperature, likely due to a decrystallization of the tails upon reverse micelle formation. The maximum particle mobilities decreased upon increasing temperature due to the increased electrostatic screening by charged reverse micelles at higher temperatures.

This paper examines the effects of solvent composition on the micellization behavior of the surfactant Aerosol OT (AOT). The critical micelle concentrations of AOT in the pure solvents methanol, ethanol, propanol, and isopropanol were measured using conductiometric techniques. These solvents were then mixed with water to create solvent spectra from pure alcohol to pure water in 12 increments. Critical micelle concentrations were measured at each solvent composition. Dynamic light scattering was used to verify the presence or absence of micelles in the solvent mixtures. It was found that inverse micelles exist over a range of solvent compositions where εeff < 48 with CMCs increasing with increasing solvent polarity. Micellization was found not to occur when 48 < εeff < 80. Regular micelles formed in pure water, with the measured CMC agreeing with the literature value of 2.25 mM.

The concurrent decomposition and deoxygenation of ethanol was accomplished in a stratified reactor with 50-80 ms contact times. The stratified reactor comprised an upstream oxidation zone that contained Pt-coated Al(2)O(3) beads and a downstream dehydration zone consisting of H-ZSM-5 zeolite films deposited on Al(2)O(3) monoliths. Ethanol conversion, product selectivity, and reactor temperature profiles were measured for a range of fuel:oxygen ratios for two autothermal reactor configurations using two different sacrificial fuel mixtures: a parallel hydrogen-ethanol feed system and a series methane-ethanol feed system. Increasing the amount of oxygen relative to the fuel resulted in a monotonic increase in ethanol conversion in both reaction zones. The majority of the converted carbon was in the form of ethylene, where the ethanol carbon-carbon bonds stayed intact while the oxygen was removed. Over 90% yield of ethylene was achieved by using methane as a sacrificial fuel. These results demonstrate that noble metals can be successfully paired with zeolites to create a stratified autothermal reactor capable of removing oxygen from biomass model compounds in a compact, continuous flow system that can be configured to have multiple feed inputs, depending on process restrictions.

This paper investigates the effects of reverse micellar core size on the particle charging behavior of a series of acidic surfactants in apolar media. A series of Span surfactants was dissolved in deuterated decane at concentrations above the critical micelle concentration. The structures of the reverse micelles were measured using small-angle neutron scattering. It was determined that as the tail length of the surfactant increased, the size of the polar reverse micellar core decreased. Tritailed surfactants formed reverse micelles with the smallest polar cores, with radii of ∼4 Å. The sizes of the polar cores were correlated with the particle charging behavior of the Span surfactant series, as measured in a previous study. It was found that reverse micelles with intermediate core sizes imparted the largest electrophoretic mobilities to the particles. Reverse micelles with very small cores did not offer a large enough polar environment to favor charge stabilization, while very large polar cores favored disproportionation reactions in the bulk, resulting in increased electrostatic screening.