Nematic phases observed in amphiphilic polyelectrolyte–surfactant aggregate solutions

Abstract

A lyotropic phase transition is observed in a water-soluble polyelectrolyte–surfactant aggregate system (polymerized cetyltrimethylammonium 4-vinylbenzoate, or pC₁₆TVB). Unlike other oppositely-charged polyelectrolyte–surfactant aggregates at the stoichiometrically-matched charge point, these aggregates do not precipitate, and instead form isotropic–nematic biphasic solutions in water. The aggregates maintain amphiphilic behavior through the phase transition and appear to maintain the structure observed in dilute solution – that of rod-like aggregates (L/d ∼ 35 with d = 4 nm). Rheology, microscopy and small-angle neutron scattering are used to verify the nature of the phase transition and structure of the mesogen. The phase transition occurs at a concentration higher than that predicted by simple theory; however, flexibility, charge repulsion and polydispersity must be considered in this system.