SHEAR-INDUCED MICELLAR CRYSTAL-STRUCTURES IN AN AQUEOUS TRIBLOCK COPOLYMER SOLUTION

Shear-induced structures have been observed in aqueous solutions of th e triblock copolymer PEO25PPO40PEO25 in the micellar crystalline regio n of the temperature-concentration phase diagram. A structure induced by steady shear, having two-dimensional (2D) hexagonal symmetry over m acroscopic dimensions, transforms reversibly to a crystalline structur e with different symmetry upon cessation of shear. Other structures ar e induced with oscillatory shear, including a 3D hexagonal phase with Bragg peaks that not only persist but sharpen with the cessation of sh ear. Over the range of temperature, concentration, and shear condition s investigated, no evidence for cubic or cubatic crystalline phases ha s been observed. [S1063-651X(98)50110-9].