DYNAMIC AND VISCOELASTIC PROPERTIES DURING THE THERMAL GELATION PROCESS OF A NONIONIC CELLULOSE ETHER DISSOLVED IN WATER-IN THE PRESENCE OFIONIC SURFACTANTS

Dynamic light scattering (DLS) and shear relaxation experiments have b een performed at various temperatures on the thermoreversible gelling aqueous systems ethyl(hydroxyethyl) cellulose (EHEC)/sodium dodecyl su lfate (SDS) and EHEC/cetyltrimethylammonium bromide (CTAB). Both the s hear relaxation modulus and the decay of the time correlation function are slowed down as the gel is formed. The DLS results indicate initia lly 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 exponen tial increases as the gel evolves.: The fast relaxation mode is found to be diffusive at all temperatures, while the slow mode exhibits a co mplex wave vector dependence. The characteristic features are the same for both systems, but the shear relaxation modulus measurements as we ll as the DLS experiments suggest that the level of chain association or entanglement is higher for the EHEC/SDS system than for the EHEC/CT AB system.