Photon Correlation Studies on the Micelles of a Poly (Oxyethylene) -Poly (Oxypropylene) -Poly (Oxyethylene) Block Copolymer in Aqueous Solution

Abstract

The micellar properties of the ABA poly(oxyethylene)- poly(oxypropylene)-poly(oxyethylene) block copolymer, Pluronic F127 have been examined by photon correlation and viscometric techniques. The hydrodynamic micellar radius calculated from diffusion data at the critical micelle concentration remains constant at 10.2 ± 0.1 nm over the temperature range. 35°–45 C. Viscometric studies have, however, shown a progressive dehydration of the micelles with temperature increase and it is clear that this dehydration must be accompanied by a concomitant increase in anhydrous volume such that the overall hydrated volume is unaffected by temperature change. Increase of solution concentration above about l0g d1^-l over this temperature range caused an apparent, marked increase of mean micellar size and of the polydispersity of micellar sizes. The relevance of these studies to the thermal gelation of this block copolymer is discussed.