on the type of the surfactant system, the surfactant The formation of shear induced structures (SIS) of a mixed concentration, and the temperature. micellar solution of tetradecyldimethylaminoxide and sodium do-Above q crit , the flow properties change dramatically. The decylsulfate is studied by light scattering experiments under shear viscosity increases and the solutions show birefringence. The (rheo-optical method). In the shear rate-as well as in the timeextinction angle of the birefringence spontaneously dedependent measurements we found an aggregation process taking creases to zero degrees (1), pointing to structure completely part in the SIS formation. Below the critical shear rate for the aligned in the direction of flow. The magnitude of q crit is occurrence of SIS, the shear rate dependent experiments show an lower than the rotational diffusion coefficient D rot (L) of indiincreased scattering intensity, indicating micellar associates.
vidual micelles of the length L. Meaning that the alignment Above the critical shear rate, we found structures oriented in the direction of flow. The time dependent measurements show that of the SIS can not be a process of just the orientation of the the SIS formation can be regarded as a process which can be individual micelles. From rheological measurements, a time divided into three stages: induction-aggregation-orientation. dependence of the increasing viscosity above q crit was de-After the aggregation, we found a temporal process in which the tected as follows. After the solution is subjected to a shear orientation increases to reach complete orientation in the direction flow q ú q crit , a delay time in the range of some seconds of flow. ᭧ 1997 Academic Press up to several minutes depending on q was observed. The Key Words: shear induced structures; light scattering; aggregaviscosity increases only after this delay time (6). tion; micelles; shear.
Our experience in laser light scattering under shear on dilute polymer solutions (8) shall now be used on SIS forming aqueous surfactant solutions. We use a ''static'' light