Mixtures containing water and a PEO–PPO–PEO block copolymer, i.e. apolyoxyethylene–polyoxypropylene–polyoxyethylene glycol, have been investigated and the phase boundaries determined.
The phase diagram shows similarities with non-ionic surfactant systems of the n-alkyl-polyoxyethylene glycol family, with occurrence of different lyotropic liquid crystalline phases and of upper consolute boundaries.
Added sodium salts have a pronounced effect on the critical solution boundaries, which can be shifted upwards (downwards), depending on the counterion. A qualitative explanation of the above effects is given in terms of adsorption and/or depletion of the electrolytes at the polar-apolar interface of the aggregates formed by block copolymers.