A Nonionic Microemulsion with Adsorbing Polyelectrolyte

Structure and interactions were investigated when small amounts of a hydrophobically modified poly(sodium acrylate) (HMPA) were added to a droplet microemulsion−lamellar system comprising nonionic surfactant. As demonstrated by small angle neutron scattering and NMR self-diffusion the aggregate structure was unaffected by HMPA, accounting for a temperature shift in the phase boundaries. Viscoelastic gels are formed in the droplet microemulsion−HMPA mixtures above a certain polyelectrolyte concentration. HMPA is soluble in the lamellar phase at high dilution. Upon increasing the bilayer concentration a phase separation is induced where excess bilayers form a separate phase. The lamellar phase with HMPA collapses when adding salt, probably as a result of bridging. A viscous microemulsion solution can be transformed to a viscoelastic gel upon increasing the temperature. A dramatic change in surfactant aggregate structure is responsible for this spectacular effect.