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 macroscopi c (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 c onsisting of a representative poly(ethylene oxide)-poly(propylene oxide)-po ly(ethylene oxide) (PEO-PPO-PEO) block copolymer (Pluronic P105, EO37PO58BE O37), water and a polar cosolvent (such as glycerol, propylene glycol or et hanol) is presented. The effect of cosolvents on the copolymer phase behavi or is quantified in terms of the highest cosolvent/water ratio able to main tain the liquid crystalline structures. The effect of cosolvents on the mic rostructure 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 microstructu re 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-assembl y 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 modifi cation of the lyotropic liquid crystalline microstructure of the PEO-PPO-PE O block copolymers is discussed in comparison to the phase behavior of the low-molecular nonionic surfactants. (C) 2001 Elsevier Science B.V. All righ ts reserved.