Dynamic and Viscoelastic Properties during the Thermal Gelation Process of a Nonionic Cellulose Ether Dissolved in Water in the Presence of Ionic Surfactants

Abstract

Dynamic light scattering (DLS) and shear relaxation experiments have been performed at various temperatures on the thermoreversible gelling aqueous systems ethyl(hydroxyethyl) cellulose (EHEC)/sodium dodecyl sulfate (SDS) and EHEC/cetyltrimethylammonium bromide (CTAB). Both the shear relaxation modulus and the decay of the time correlation function are slowed down as the gel is formed. The DLS results indicate initially an exponential decay followed by a stretched exponential at longer times. The relaxation time of the fast mode decreases with increasing temperature, whereas the characteristic time of the stretched exponential increases as the gel evolves. The fast relaxation mode is found to be diffusive at all temperatures, while the slow mode exhibits a complex wave vector dependence. The characteristic features are the same for both systems, but the shear relaxation modulus measurements as well as the DLS experiments suggest that the level of chain association or entanglement is higher for the EHEC/SDS system than for the EHEC/CTAB system.