Electrostatic free energy and shift of the phase transition for charged lipid membranes

For a charged membrane in an electrolyte solution the electrostatic free energy is derived treating the system as a diffuse double layer. The dependence of the energy on external parameters like surface charge density and temperature is obtained and the physical basis discussed. As an application the charges are shown to exert an electrostatic surface pressure on the lipid chain packing which leads to a shift in the phase transition of membranes. The results confirm the interpretation of experimental data as given by Träuble et al. in the accompanying paper.