TRANSIENT AND STEADY FLOW OF A LAMELLAR LIQUID-CRYSTALLINE SURFACTANTWATER-SYSTEM

Transient and steady flow experiments were,carried out on liquid cryst alline samples of poly(oxyethylene) alcohol/water systems, at differen t temperatures and concentrations within the lamellar phase region. Fr om the experimental results we may deduce that the transient response is very complex, showing both a stress overshoot and an undershoot, de pending on the cooperative effects of shear rate, surfactant concentra tion, and temperature. Moreover, the steady flow behavior depends dram atically on the shear history of the samples. These results have been related to the appearance of a mechanically induced structure, favored by the proximity to phase transition regions (cubic-lamellar phase an d micellar-lamellar phase).