Charged Bilayer Membranes in Asymmetric Ionic Solutions:
Phase Diagrams and Critical Behavior
Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan
Department of Chemistry, Graduate School of Science and Engineering,
Tokyo Metropolitan University, Tokyo 192-0397, Japan
Raymond and Beverly Sackler School of Physics and Astronomy,
Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel
We consider the phase separation in an asymmetrically charged lipid bilayer membrane consisting
of neutral and negatively charged lipids that are in contact with in/out ionic solutions having
different ionic strengths. The two asymmetric leaflets are coupled through electrostatic interactions.
Based on a free energy approach, the critical point and phase diagrams are calculated for different
ionic strength of the two solutions and coupling parameter. An increase of the coupling constant or
asymmetry in the salt concentration between the in/out solutions yields a higher phase separation
temperature because of electrostatic interactions. As a consequence, the phase-coexistence region
increases for strong screening (small Debye length). Finally, possible three-phase coexistence regions
in the phase diagram are predicted.