Structural Polymorphism of Amphiphilic Block Copolymers in Mixtures with Water and Oil: Comparison with Solvent-Free Block Copolymers and Surfactant Systems

Abstract

This chapter discusses the phase behavior and microstructure of poly (ethylene oxide)-poly (propylene oxide) (PEO-PPO) block copolymers in water and oil. Binary or ternary mixtures of amphiphilic PEO-PPO block copolymers and one or two solvents selective for the PEO and/or the PPO blocks exhibit a very rich structural polymorphism. The microstructure resulting from the self assembly of the solvated block copolymers can vary from normal (PPO + oil core) micelles in solution, through all types of normal and reverse (PEO + water core) lyotropic liquid crystals (normal micellar cubic, hexagonal, and bicontinuous cubic, lamellar, reverse bicontinuous cubic, hexagonal, and micellar cubic), to reverse micelles in solution, as the relative volume fraction of the “PPO”-like (that is, PPO plus its selective solvent) components increases over that of the “PEO”-like components, and the polymer blocks swell to different extents, and thus modulate the interfacial “curvature.” Recent findings on the phase behavior and structure of solvated block copolymers are reviewed in the chapter. These results are placed in the context of the morphology observed in block copolymer blends and in surfactant–water–oil systems. The morphological versatility of block copolymers, which is promoted by the addition of selective solvents, has repercussions on aspects both fundamental and applied/practical.