Pressure-Induced Phase Transitions of Hydrophobically Solvated Block-Copolymer Solutions

The structures of poly(2-(2-ethoxy)ethoxyethyl vinyl ether)-block-poly(2-methoxyethyl vinyl ether) in D2O have been investigated with small-angle neutron scattering (SANS) as a function of temperature T and pressure P. At ambient pressure, the solution underwent a two-step transition at 40 and 65 degrees C, both of which were convex-upward functions of P having a maximum around P0 approximately 150 MPa. The first transition was assigned to a microphase separation to form a bcc structure, and the second was to a macrophase separation. Pressurizing at 28 degrees C resulted in a macrophase separation with divergence at 350 MPa. At 45 degrees C, a reentrant microphase separation was observed by increasing P. Differences in the states of hydrophobic solvation in the low (P P0) are discussed based on the SANS structure factors.