FORCES BETWEEN MACROSCOPIC SURFACES IN A SPONGE PHASE

We present measurements of forces between macroscopic mica surfaces immersed in a series of AOT-NaNO3-water samples of a sponge (L3) phase. We observe a long ranged oscillatory force which exhibits two distinct regions. At large separations, 400-1200 angstrom, the period of the oscillations is concentration dependent and the effect is due to structure in the bulk solution. In a confined space, at separations smaller than approximately 300 angstrom, there is a topological transition to a layer structure with a force having huge repulsive barriers with a period of 30-35 angstrom, virtually independent of concentration.