Osmotic pressure and salt exclusion in electrostatically swollen lamellar phases

Measurements of osmotic pressure, mainly of electrostatic origin, are reported in the diluted regime of charged bilayers. The interlamellar distances (100–1000 Å) are measured using small-angle neutron scattering. The electrostatic repulsive pressure is evaluated within the framework of the Poisson–Boltzmann model, taking into account the conditions of ionic conservation and electrochemical equilibrium, and checked by Monte Carlo simulations in the grand canonical ensemble. The predicted phenomenon of salt ejection from the bilayers is evidenced by direct chemical analysis. Implications concerning the phase behavior of double-tailed surfactants are discussed.