Phase behaviour and rheological properties of the lamellar liquid crystals formed in dodecyl polyoxyethylene polyoxypropylene ether/water system

The temperature-composition phase diagram of the binary nonionic surfactant dodecyl polyoxyethylene polyoxypropylene ether/water system has been determined from 10 degrees C to 70 degrees C. Two domains of lamellar liquid crystal phase are found in the binary system as the concentration of the nonionic surfactant increases. The phase boundary of the lamellar phase in the phase diagram has been identified by differential thermal analysis. The steady and dynamic rheological properties of the lamellar liquid crystals have been studied. Steady shear rheology results indicate that the lamellar liquid crystals show shear-thinning behavior, and behave as a plastic system with the in parameter between 0.6 and 0.7 in the empirical equation. sigma = sigma(HB) + K gamma(m). Dynamic rheological results show that the lamellar phase exhibits a typical gel-like rheogram. With increase in surfactant content, the dynamic modulus increases, while with increases in temperature, the dynamic modulus decreases.