Effects of Temperature, Surfactant Concentration, and Salinity on the Dynamics of Dilute Solutions of a Nonionic Cellulose Derivative

Abstract

The interaction between sodium dodecyl sulfate (SDS) and ethyl(hydroxyethyl)cellulose (EHEC) has been studied as a function of temperature in dilute aqueous solutions in the presence of various amounts of SDS and at some different levels of NaCl addition with the aid of dynamic light scattering (DLS). The DLS results suggest initially an exponential decay followed by a stretched exponential at longer times. The fast mode is always diffusive, and the results are presented in terms of the hydrodynamic radius. The slow mode exhibits a stronger and more complex wave vector dependence than the fast mode. The interaction between the polymer and surfactant gives rise to the formation of polymer−surfactant clusters at low levels of surfactant addition. The cluster size increases at low surfactant concentrations and passes through a maximum slightly above the critical aggregation concentration. In this process, the interplay between swelling and deaggregation of the clusters plays an important role. The position of the maximum is shifted toward lower SDS concentrations with increasing temperature. At low levels of surfactant addition, the growth of the aggregates is promoted by increasing temperature and salinity. As the surfactant concentration increases, the aggregates gradually become disrupted and the impact of temperature and salinity on the size of the polymer aggregates becomes small.