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An equilibrium phase belonging to the family of bilayer liposomes in ternary mixtures of dimyristoylphosphatidylcholine (DMPC), water, and geraniol (a biological alcohol derived from oil-soluble vitamins that acts as a cosurfactant) has been identified. Electron and optical microscopy reveal the phase, labeled L tv , to be composed of highly entangled tubular vesicles. In situ x-ray diffraction confirms that the tubule walls are multilamellar with the lipids in the chain-melted state. Macroscopic observations show that the L tv phase coexists with the well-known L 4 phase of spherical vesicles and a bulk L α phase. However, the defining characteristic of the L tv phase is the Weissenberg rod climbing effect under shear, which results from its polymer-like entangled microstructure.

The forces between bilayers self-assembled onto mica from dilute aqueous solutions containing vesicles of mixed cationic surfactant cetyltrimethylammoniun tosylate (CTAT) and anionic surfactant sodium dodecylbgnzenesulfonate (SDBS) were measured using the surface forces apparatus. At large separations (D > 20 A) the forces can be described by the DLVO theory of repulsive electrostatic and attractive van der Waals forces; in dilute solution, the electrostatic repulsion is sufficient to make the net interaction ofthe mixed surfactant bilayers repulsive at all separations. The electrostatic force dominates any undulation or other long-range interactions and is sufficient to render the vesicles stable against aggregation in dilute solution. Although the net interactions between the mixed surfactant bilayers were monotonically repulsive, fusion of the bilayers could be induced at applied pressures orders of magnitude lower than for singlecomponent phospholipid or surfactant bilayers. At sufficiently high concentrations of added salt ('0.5 M), the electrostatic interactions were screened sufficiently that multilayers were trapped between the surfaces. The measured forces correlate well with the ternary phase diagram and thevesicle microstructures observed using freeze-fracture and cryo-electron microscopy.

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