LIGHT-SCATTERING-STUDIES OF A BLOCK POLY(OXYETHYLENE OXYPROPYLENE OXYETHYLENE) COPOLYMER IN WATER O-XYLENE MIXTURES

Laser light scattering was used to investigate the micellization, the supramolecular formation, and the pregelation process of a PEO-PPO-PEO copolymer (Pluronic L64) in water/o-xylene mixtures over the temperature range 21-45-degrees-C. Large aggregates could coexist with small micelles and unimers at high concentrations. It was found that the micellar size remained essentially the same from dilute to concentrated solutions. However, differing from PEO-PPO-PEO copolymers in pure water, the secondary large aggregates were formed by micelle association, not close-packing. The copolymer concentration and the amount of solubilized water determined both the number and the size of the secondary large aggregates. While the effect of temperature on the micelles was much smaller than that on the large aggregates, the amount and the size of the large aggregates decreased with increasing temperature. An open-association mechanism is proposed for the equilibrium between the micelles and the secondary large aggregates.