Thermodynamics of the L3 (Sponge) Phase in the Flexible Surface Model

John Daicic , Ulf Olsson , Hakan Wennerström , Götz Jerke , Peter Schurtenberger

The thermodynamics of the L3 (sponge) phase is investigated within the flexible surface model. The well-established leading-order Φ3 scaling for the free energy density (where Φ is the surfactant volume fraction) requires modification in order to describe the narrow character of the phase and the observed sequence of phase transitions. We find that higher order contributions to the free energy density from the local curvature energy provide a straightforward mechanism to account for these features. The phase equilibria with the dilute solution on one side of the phase and the lamellar phase on the other are evaluated for a model binary (surfactant-solvent) system, and calculated phase diagrams are presented. Experimental evidence in support of the model comes from static light scattering experiments on the pseudo-binary system AOT-NaNO3-water. We calculate the forward scattering intensity along chosen dilution lines within the phase using the model, and predict that the scattering intensity varies significantly as we move from one phase boundary to the other at constant Φ. The experimental results confirm these predictions, and provide strong evidence in support of the proposed model.

Domaines: Articles anciens

John Daicic, Ulf Olsson, Hakan Wennerström, Götz Jerke, Peter Schurtenberger. Thermodynamics of the L3 (Sponge) Phase in the Flexible Surface Model. Journal de Physique II, 1995, 5 (2), pp.199-215. ⟨10.1051/jp2:1995123⟩. ⟨jpa-00248148⟩