Shear-induced micellar crystal structures in an aqueous triblock copolymer solution

Abstract

Shear-induced structures have been observed in aqueous solutions of the triblock copolymer ${\mathrm{PEO}}_{25}{\mathrm{PPO}}_{40}{\mathrm{PEO}}_{25}$ in the micellar crystalline region of the temperature-concentration phase diagram. A structure induced by steady shear, having two-dimensional (2D) hexagonal symmetry over macroscopic dimensions, transforms reversibly to a crystalline structure with different symmetry upon cessation of shear. Other structures are induced with oscillatory shear, including a 3D hexagonal phase with Bragg peaks that not only persist but sharpen with the cessation of shear. Over the range of temperature, concentration, and shear conditions investigated, no evidence for cubic or cubatic crystalline phases has been observed.