SHEAR ORIENTATION OF A HEXAGONAL LYOTROPIC TRIBLOCK COPOLYMER PHASE AS PROBED BY FLOW BIREFRINGENCE AND SMALL-ANGLE LIGHT AND NEUTRON-SCATTERING

The shear orientation of the hexagonal liquid crystalline phase of a p oloxamer-type triblock copolymer (poly(ethylene oxide)-b-poly(propylen e oxide)-b-poly(ethylene oxide) (Pluronic L64))/water mixture was inve stigated by means of different techniques, namely, flow birefringence (Delta n), small-angle light scattering, and small-angle neutron scatt ering (SALS, SANS). The evolution of birefringence is discussed for di fferent types of shear. Oscillatory shear showed that birefringence di splayed small oscillations during the first cycles until the sample wa s shear aligned. Then the same an value was obtained as in creep exper iments. The degree of orientation depended on the strain. On a microsc opic length scale probed by SANS, the shear flow results in an alignme nt of rodlike micelles along the flow direction. SANS experiments with the incident beam along the now direction revealed that the 10 plane of the hexagonal lattice was aligned parallel to the flow-vorticity pl ane. On a mesoscopic length scale, studied by microscopy and SALS, a s tripe texture was observed. SALS showed that the texture was similar t o that obtained in low molar mass surfactants.