Clouding behavior of ethylene oxide-propylene oxide (EPE and PEP) block copolymer solutions in water

The cloud point (CP) data on aqueous solutions of polyethylene oxide - polypropylene oxide block copolymers [PEO-PPO-PEO abbreviated as EPE and PPO-PEO-PPO abbreviated as PEP] and their mixtures at different concentrations are reported. The effect of several additives viz. electrolytes, hydrotropes and ionic surfactants on the CP of the copolymers is also examined. Electrolytes showed an increase/decrease in cloud point based on their,salting in' and 'salting out' action and follow the Hofmeister/lyotropic series. Hydrotropes increase CP by influencing water structure at much lower concentration than inorganic salts. Ionic surfactants produce a marked increase in the cloud point of copolymer solutions at concentrations much less than their critical micelle concentration; the effect was more for surfactants with greater hydrophobicity.