Dynamic Light Scattering of a Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Triblock Copolymer in Water

Abstract

Dynamic light scattering experiments have been performed at various temperatures on nongelling aqueous solutions of Pluronic F68 and on a concentrated sample that undergoes a temperature-induced sol−gel transition. At certain concentrations and temperatures the time correlation data revealed the existence of two relaxation modes: a single exponential at short time and a stretched exponential tail at long times, while at other conditions of temperature and concentration, a power law appeared at intermediate times in the profile of the decay of the correlation function. The results show that the power law behavior is not restricted to incipient gels but can also arise in moderately viscous solutions. The emergence of the power law is favored by elevated temperature and/or increased concentration. The width of the power law window depends on concentration and temperature. The value of the power law exponent is dependent on concentration, temperature, and scattering angle.