MICELLE AND GEL FORMATION IN A POLY(ETHYLENE OXIDE) POLY(PROPYLENE OXIDE) POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMER IN WATER SOLUTION - DYNAMIC AND STATIC LIGHT-SCATTERING AND OSCILLATORY SHEAR MEASUREMENTS

The properties of aqueous solutions of low molecular weight triblock copolymers of PEO/PPO/PEO have been investigated, mainly by dynamic and static light scattering. At low concentrations (C < 10%) and temperature (< 25-degrees-C) the relaxation time distributions from dynamic light scattering show the coexistence of the monomer (R(H) almost-equal-to 18 angstrom), micelles (R(H) almost-equal-to 80 angstrom), and micellar aggregates in relative proportions which depend critically on temperature and concentration. Micelles are formed at about C = 5% at 25-degrees-C. At 40-degrees-C and above micelles are present at all concentrations used (C > 0.3%). At infinite dilution the hydrodynamic radius of the micelles is approximately constant over the temperature range 15-50-degrees-C. At finite concentrations the apparent micellar radius increases with increasing temperature. The growth into asymmetric particles with increasing concentration is stronger as demonstrated by ultracentrifugation and combining static and dynamic light scattering data. At higher concentrations, a solidlike gel is formed at a well-defined temperature as shown by oscillatory shear measurements. It is characterized by a dynamic correlation length which decreases monotonically with increasing concentration to about 20 angstrom.