Modification of the lyotropic liquid crystalline microstructure of amphiphilic block copolymers in the presence of cosolvents

This article reviews the results of recent investigations on the macroscopic (phase behavior) and microscopic (microstructure) aspects of the role of cosolvents on the self-assembly of amphiphilic copolymers. A comprehensive account of the systematic studies performed in ternary isothermal systems consisting of a representative poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer (Pluronic P105, EO37PO58BEO37), water and a polar cosolvent (such as glycerol, propylene glycol or ethanol) is presented. The effect of cosolvents on the copolymer phase behavior is quantified in terms of the highest cosolvent/water ratio able to maintain the liquid crystalline structures. The effect of cosolvents on the microstructure of the lyotropic liquid crystals is quantified in terms of the degree of relative swelling per cosolvent content per copolymer content, a parameter that characterizes the given cosolvent and copolymer. The set of correlations on the cosolvent effects on the phase behavior or microstructure to the cosolvent physicochemical characteristics (such as octanol/water partition coefficient or solubility parameter) have led to the development of a hypothesis that accounts for the cosolvent effects on the self-assembly of PEO-PPO-PEO block copolymers and can be used to predict them. The rich structural diversity and the potential for a precise and convenient modification of the lyotropic liquid crystalline microstructure of the PEO-PPO-PEO block copolymers is discussed in comparison to the phase behavior of the low-molecular nonionic surfactants. (C) 2001 Elsevier Science B.V. All rights reserved.