KINETIC-STUDIES OF A SHEAR THICKENING MICELLAR SOLUTION

The time-dependent rheological behavior of a mixed micellar solution of tetradecyldimethylaminoxide and sodium dodecylsulfate with added salt is studied. Upon applying a constant shear flow, the shear stress begins to increase with time after an extraordinarily long initial induction period (on the order of tens of seconds) which is inversely proportional to the shear rate. The stress eventually reaches a plateau which fluctuates randomly over a narrow range, and the time required to achieve this decreases with shear rate according to a power law. The flow birefringence and extinction angle are also measured as a function of time. The unusually slow buildup of stress occurs only if the applied shear rate exceeds a critical value above which shear thickening takes place. It is suggested that shear induced coagulation among rodlike micelles as a kinetic process is consistent with the experimental observations. © 1993 Academic Press, Inc.