Hole-mediated stability and permeability of bilayers

Abstract

Abstract Membrane, foam and emulsion bilayers are considered from a unified point of view as two-dimensional phases and their stability with respect to rupture and permeability with regard to molecular species is analysed with the help of the fluctuation theory of nucleation of holes in them. Molecular models of bilayers are described and both the thermodynamics and the kinetics of the ‘condensation’ of the two-dimensional ‘gas’ of vacancies in a bilayer are outlined. It is shown how the bilayer mean lifetime τ, the probability W of observing a foam bilayer in a thicker foam film and the bilayer diffusion permeability coefficient P d depend on the concentration C of monomer amphiphiles in the surrounding solution. The effect of various factors (particularly α-particle irradiation and an externally applied electric field) on τ and P d is also discussed. Experimental techniques for investigating foam films are described and experimental data on τ(C), W(C) and Pd(C) are presented for bilayers of lipids and s...