Investigation of the L-3 phase in systems containing calcium dodecyl sulfate, alcohol, and water

An isotropic, clear phase at high alcohol content is found in a system comp osed of calcium dodecyl sulfate, water, and an alcohol of medium chain leng th, like pentanol. hexanol, heptanol, or octanol. This phase is located in that region of the phase diagram in which L-3 phases are classically formed . Most ionic surfactants, however, only form sponge phases when the ionic c harge of the surfactant molecules is sufficiently shielded by excess salt. At 5% surfactant and octanol as cosurfactant, the L-3 phase disappears if m ore than 5% of the calcium ions are substituted by sodium. Calcium dodecyl sulfate, in some aspects, behaves like a nonionic or double-chain surfactan t. The phase discussed in this article is completely transparent, has low v iscosity, and exhibits neither birefringence nor yield stress. Viscosity, e lectrical conductivity, and freeze-fracture electron microscopy indicate th e sponge structure of the phase. In contrast to typical L-3 phases, small-a ngle neutron-scattering experiments show a peak the position of which is ne arly unshifted compared with that of the neighboring lamellar phase.