RHEOLOGICAL STUDY OF TERNARY CUBIC PHASES

We have studied the theology of bicontinuous ternary cubic phases form ed by the system didode-cyldimethylammonium bromide (DDAB)/D2O/octane. The cubic samples have the appearance and texture of optically clear, isotropic, highly viscous gels. The microstructure of these cubic pha ses is such that the surfactant bilayer containing the paraffinic tail s and the oil may be visualized as decorating a minimal surface so tha t the latter constitutes the mid-surface bisecting the bilayer. Linear theology confirms that the dissipation becomes low at high acoustic f requencies and is consistent with the phenomenon of ''ringing'' in whi ch underdamped shear modes in the gel couple to sound via the gel surf ace. The frequency-dependent theology also reveals a universal scaling form bt the melting transition of the cubic phase, with the dynamical scaling observed at this point reminiscent of a percolation transitio n. Nonlinear theological response is consistent with the formation of dislocation or slip-planes in the cubic structure, parallel to the dir ection of shear. The experimental observations are related to the dyna mics of the water/surfactant/oil interface, and theoretical ideas are presented to account for the observed behavior. Our results suggest th at frequency dependent theology is a useful structural probe of the dy namics of ternary cubic phases;