Relaxation Kinetics of an L3(Sponge) Phase

Abstract

The kinetic response of an L3 (sponge) phase formed in the C12E5−n-decane−brine system is studied using the Joule-heating temperature jump (JHTJ) technique. The equilibrium state of the spongelike membrane is instantaneously perturbed, and the kinetic response is monitored using a multi-angle light scattering setup. These measurements yield a time-dependent scattering intensity as a function of temperature, scattering vector q, and concentration. We observed a single-exponential relaxation characteristic time, τm. The q dependence of the scattering amplitude shows an Ornstein−Zernike behavior, but we can identify two concentration regimes with respect to the relaxation behavior. For volume fractions Φm = 0.20, there is no detectable q dependence of the relaxation times, while for samples with Φm > 0.30, the relaxation times display the q-2 dependence typical of a diffusive process and with relaxation times consistent with those found in dynamic light scattering. At the intermediate concentrations, there is a transition from the q-independent to the q-2 dependence behavior. Analysis from each concentration regime reveals distinct differences in the dependence of τm on temperature and concentration, with an extraordinarily strong concentration dependence of τm (τm ≈ Φ-9) in the low concentration regime and a temperature dependence corresponding to a formal Arrhenius activation energy of 720 kJ/mol or 275 kT.