Abstract:
The phase diagram of the mixed zwitterionic/anionic surfactant system hexadecyldimethyl-
ammoniopropancsulphonate/sodium dodecyl sulphate/water has been determined in the aqueous
region (>90.0 % water) by optical microscopy and low angle X-ray scattering; the phases observed
were an isotropic surfactant solution and a hexagonal liquid crystalline phase. Some aqueous
solutions were found to be viscoelastic and the composition boundaries of solutions with these
properties were parallel to the phase boundaries. N.m.r. was used additionally to study the structure
of the viscoelastic solutions and the results are interpreted using a model which involves the existence
of both normal spherical micelles and cylindrical micelles in equilibrium.
