Langmuir 1985,1, 387-390
387
to maintain the particle in the center of the balance with the electrical field. Flow instabilities and vortex shedding which occur a t higher Reynolds numbers can result in transport of the particle out of the chamber. The flow experiments performed indicate that reasonably large flow rates can be used without losing the particle. This makes it possible to study convective mass transfer, and we have made measurements of mass transfer rates for pinene evaporating into flowing nitrogen. Furthermore, the electrodynamic balance can be used as a chemical reactor for gas-particle chemical reaction studies, for a reactive gas can be passed through the balance chamber.
theory used to determine the marginal stability curve is based on creeping flow. Experimentally, operation of the balance is aided by the effect of higher order terms on the drag. Because of higher order terms (see eq 54) a particle oscillating in the unstable regime experiences a larger drag force than that used in the derivation of the stability theory. The result is that it is frequently possible to operate in the unstable regions of Figure 2 without losing the particle. In fact, we have found it possible to increase the ac voltage beyond that corresponding to region 1of Figure 2 and have the particle undergo a large-amplitude oscillation, reach the next stable region, and become unstable again as the voltage is increased. The flow technique is not limited to low Reynolds numbers, so it is more appropriate to use for the study of aerodynamic drag over a fairly wide range of Reynolda numbers. The only limit to the flow method is the abilit;
Acknowledgment. This work was supported by the Defense Nuclear Agency under Contracts DNA 001-82-C0224 and DNA 001-84-C-0293.
Vesicles from Dimer Acid and Its Derivatives? Jiirgen-Hinrich Fuhrhop,*$ Winfried Kaufmann,t and Fred Schambils Institut fur Organische Chemie der Freien Universitat Berlin, 0-1000 Berlin 33, West Germany, and Forschungslaboratorium Henkel KGaA,
0-4000 Diisseldorf 1 , West Germany Received July 6,1984. In Final Form: February 1, 1985 Commercial dimer acid is the only nonexpensive a,w-dicarboxylicacid of appropriate chain length for the formation of vesicle membranes. The acid itself is water insoluble and does not form vesicles on sonication. Addition of cyclohexylamine or amide formation with aniline-2-sulfonic acid, however, converts dimer acid into a vesicle forming bolaamphiphile. Analogous results have been obtained by using esters of commercial dimer alcohol and pyromellitic acid. A stable gel, which produces a vesicular solution on dilution with water, is also described. Dimer acid derivatives constitute candidates for large-scale applications of vesicles.
Introduction Vesicles are sealed, extremely thin (110 nm) membranes of spherical shape, which enclose water volumes of approximately 1-1000 pm3.1v2 Various amphiphiles may aggregate to vesicles with critical concentrations in the range of
