A CONFINED COMPLEX LIQUID - OSCILLATORY FORCES AND LAMELLAE FORMATIONFROM AN L(3) PHASE

In this paper, we present the results from measurements of forces betw een macroscopic mica surfaces immersed in an L(3) (sponge) phase. Two different surfactant systems are investigated. As previously reported (Petrov, P.; et al. Langmuir 1994, 10, 988) for the AOT/brine/water L( 3) phase, two distinct regions in the force profile are observed: At l arge separations (40-120 nm), the force is oscillatory due to the stru cture in the bulk solution. In a confined space, at separations smalle r than similar to 30 nm, there is a topological transition to a layere d, lamellar-like structure with a force having huge repulsive barriers with a period of 3-3.5 nm, weakly dependent on concentration. The sam e characteristic forces are observed for an L(3) phase made of C(12)E( 5)/hexanol/water. The period of long-range oscillations, scaled by the thickness of the bilayer, is inversely proportional to the surfactant volume fraction and shows a uniform functional dependence for both L( 3)-phase systems, in accordance with the general scaling law. Model ca lculations of the force profile within the flexible surface model repr oduce and rationalize all qualitative observations and give a reasonab le quantitative estimate of the force. We derive generally applicable conditions for the appearance of a stable lens of lamellar phase betwe en curved surfaces in a bulk L(3) solution and calculate the force exp licitly, without invoking the Derjaguin approximation.