HEXAGONAL-TO-LAMELLAR PHASE-TRANSITION INDUCED BY ADDITION OF A RANDOM HETEROPOLYMER TO THE SURFACTANT-WATER SYSTEM

We report on the microstructural study in a cross section of the terna ry phase diagram of pentaethylene glycol mono-n-dodecyl ether (C12E5)/ water/random heteropolymer defined by the surfactant-to-water ratio eq ual to unity and constant temperature of 21 degrees C. The transformat ion from a normal hexagonal to a lamellar phase is observed as a funct ion of increasing polymer content. The small-angle X-ray scattering re sults demonstrate the presence of a well-defined hexagonal structure u p to about 1 wt % of polymer content that transforms into a lamellar s tructure at 7.7 wt % of polymer, as evidenced by two harmonics present in the scattering spectrum. There is no two-phase region observed. Fr eeze fracture electron microscopy images demonstrate the presence of a hexagonal phase up to the polymer concentration of 1.0 wt % and a lam ellar phase for higher polymer concentrations (1.6 wt % and above). Th e polymer molecules are confined inside the surfactant bilayers of a l amellar phase. The textures seen using polarizing microscopy provide a strong supportive argument for a gradual change of topology with the addition of polymer.