Shear effects on the morphology transition in a nonionic surfactant system

We report the small angle neutron scattering studies on the lamellar-to-gyr oid morphology transition in a nonionic surfactant system under shear flow condition. The morphology transition is suppressed by the shear flow when t he shear rate exceeds a critical value. This means that the shear field sup presses the undulation fluctuation of lamellar the structure above the crit ical shear rate. On the contrary when we applied shear flow in the gyroid p hase, the shear-induced gyroid-to-lamellar transition was observed above th e critical shear rate. The critical shear rate for the suppression of the u ndulation fluctuation agrees with the critical shear rate for shear induced gyroid-to-lamellar transition. (C) 1999 Elsevier Science Ltd. All rights r eserved.