Conformation of poly(ethylene oxide) in polymer-surfactant aggregates

The influence of sodium dodecyl sulfate (SDS) on the conformation of poly(ethylene oxide) (PEO) in water is studied using viscosity measurements and small-angle neutron scattering (SANS). The behavior, as a function of surfactant concentration above the critical aggregation concentration (CAC), can be described in terms of two separate regimes:  an initial regime in which micelles are attached to the coils but are noninteracting and a second regime in which there is interaction between the attached micelles. The latter is characterized by a strong increase in viscosity and other features similar to polyelectrolytes. On the contrary, in the initial regime, our results suggest a slight decrease in coil size under ambient conditions and a much more significant decrease at elevated temperatures. The cloud point of PEO in water exhibits a minimum as a function of surfactant concentration. We believe the minimum in the cloud point corresponds to a crossover from the noninteracting to the interacting regime.