Inverse melting transition and evidence of three-dimensional cubatic structure in a block-copolymer micellar system

Abstract

Structural studies on aqueous solutions of PEO-PPO-PEO block copolymers show three phases as the temperature is varied. At low T, the tri-block units are dissolved Gaussian chains. As T is increased still more unimers aggregate in micelles, until a volume fraction of 0.52 is reached. The micelles then crystallize in a body-centered-cubic lattice. Upon the application of a small shear, the high-T polycrystalline phase abruptly transforms into a single crystal, characterized by only quasi-long-range order in bond length, but true long-range correlations in the bond angle.