Lamellar phase coexistence induced by electrostatic interactions

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 31; no. 2; pp. 207 - 214
• Main Authors: Jho, Y. S., Kim, M. W., Safran, S. A., Pincus, P. A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-02-2010; EDP Sciences
• Subjects: Biological and Medical Physics; Biophysics; Chemistry; Colloidal state and disperse state; Complex Fluids and Microfluidics; Complex Systems; Computer Simulation; Exact sciences and technology; General and physical chemistry; Lipid Bilayers - chemistry; Membrane Fluidity; Membranes; Models, Chemical; Models, Molecular; Nanotechnology; Phase Transition; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Soft and Granular Matter; Static Electricity; Surfaces and Interfaces; Thin Films; Surface Charge Density; Phase Coexistence; Condensed Phase; Intermembrane Spacing; Equilibrium Distance; Charge density; Water; Phase separation; Electrostatic interaction; Counter ion; Membrane; Numerical simulation; Entropy; Thermodynamic properties; Electrostatics; Free energy; Thermodynamic equilibrium
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2010-10567-5

Membranes containing highly charged biomolecules can have a minimal free-energy state at small separations that originates in the strongly correlated electrostatic interactions mediated by counterions. This phenomenon can lead to a condensed, lamellar phase of charged membranes that coexists in thermodynamic equilibrium with a very dilute membrane phase. Although the dilute phase is mostly water, entropy dictates that this phase must contain some membranes and counterions. Thus, electrostatics alone can give rise to the coexistence of a condensed and an unbound lamellar phase. We use numerical simulations to predict the nature of this coexistence when the charge density of the membrane is large, for the case of multivalent counterions and for a membrane charge that is characteristic of biomolecules. We also investigate the effects of counterion size and salt on the two coexisting phases. With increasing salt concentration, we predict that electrostatic screening by salt can destroy the phase separation.