Static and dynamic light scattering studies are presented on the temperature induced sol gel transition of an aqueous system of the non-ionic cellulose derivative ethyl hydroxyethyl cellulose in the presence of a cationic surfactant. In dilute solution coil expansion is observed with increasing temperature. In the semidilute range structural changes of the network are found when approaching the sol-gel transition. These effects are explained by an enhanced binding of surfactant to the polymer. The relaxation of the correlation function, in the semidilute regime~ is shifted towards longer times as the gelation threshold is approached. These results are interpreted in the framework of a model that has been constructed with the aid of the theoretical approach of Semenov. In this model the correlation function initially decays by a fast cooperative mode (single exponential ), followed by a non-exponential decay (reptation-like mode) at longer times. The cooperative relaxation time is only slightly influenced by temperature, whereas the reptation-like relaxation time exhibits a drastic increase during the gelation process. This effect is attributed to a slowing down of the motion of the individual chains in the gelation zone. Within the framework of the model the determination of the gel point seems possible.
Посилання на статтю:
Light scattering studies of the gelation process in an aqueous system of a non-ionic polymer and a cationic surfactant / Bo Nystrom* and Jaan Roots and Anders Carlsson+ and Bj6rn Lindman // Polymer. – 1992. – Vol 33. – P. 2875-2882.