Clouding & micellar behavior of ethylene oxide-propylene oxide-ethylene oxide (EPE and PEP) block copolymers & their mixtures from aqueous solution

Surface tension, cloud point and viscosity techniques were used to examine micellar and phase behavior of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers (PEO-PPO-PEO abbreviated as EPE and PPO-PEO-PPO as PEP) and their mixtures at different concentrations in absence and presence of NaCl and urea. While the addition of NaCl lowered the CMC, cloud point and viscosity, the addition of urea showed the reverse trend. The presence of NaCl develops hydrophobicity of PPO moiety and reduces hydrophilicity of PEO moieties favoring micellization of the block copolymers at lower concentration than in water at ambient temperature. The increase in CMC, cloud point and viscosity of both the copolymers in the presence of urea is interpreted in terms of enhanced solubility of semipolar PPO moiety and also PEO moiety. Cloud point measurements were also performed for both the copolymers in presence of sodium halides (NaX, where X = F, Cl, Br and I).