Phase and rheological behavior of the allyldimethyldodecylammonium bromide water system

The temperature-composition phase diagram of water and the polymerizable surfactant, allyldimethyldodecylammonium bromide (ADDAB), is reported. At room temperature, dried ADDAB is a triclinic crystal with four molecules of surfactant (and approximately one trapped water molecule) per elementary cell. Upon heating, dried ADDAB follows the sequence: crystal-->smectic phase-->isotropic phase. At room temperature, ADDAB and water form a micellar (L-1) solution up to 53 wt% surfactant. Above this concentration and up to 89 wt%, an hexagonal (H-1) phase forms. At even higher concentrations, an isotropic highly viscous phase forms (V). Upon heating, the hexagonal phase changes into the L-1 solution whereas the V phase transforms into a lamellar (L) phase. In the high ADDAB concentration region, three types of water were detected by Fourier transform infrared spectroscopy: free; interfacial; and bound water. Steady shear and dynamical rheological functions show discontinuities at the phase boundaries suggesting that they are sensitive probes to investigate phase behavior. (C) 1998 Elsevier Science B.V. All rights reserved.