Double-diamond phase in amphiphilic systems confined between parallel walls

Effects of confinement on the cubic bicontinuous phase with double-diamond symmetry (D) are studied. We focus on a slit geometry and on highly selecti ve external walls. We show that the period of the solvation force in differ ent systems containing amphiphilic molecules can be found on simple symmetr y grounds. The simple symmetry-based predictions are verified by explicit c alculations in a lattice model for oil-water-surfactant mixtures. The expli cit results obtained within the model allow for a detailed description of t he effects of the confinement on the structure of the D phase. The structur e of the D phase with the face of the unit cell parallel to the external wa ll is shown and discussed for slits ranging from very narrow to very large ones. (C) 2001 American Institute of Physics.