SOFT AND REPULSIVE: RELATIONSHIP BETWEEN LIPID MEMBRANE IN-PLANE FLUCTUATIONS, BENDING RIGIDITY, AND REPULSIVE UNDULATION FORCES

Abstract

Lipid membranes are soft and flexible bilayer surfaces that exhibit a substantial degree of in-plane fluctuations which become very strong near lipid phase transitions and in phase separation regions. The fluctuations couple to the out-of-plane motions as well as the large-scale mechanical modulii of the membrane leading to a thermal renormalization of, e.g., the bending rigidity. For multilamellar arrays of membranes, changes in the bending rigidity in turn lead to changes in the entropic repulsive undulation forces that act between the lamellae and which determine their swelling behavior. We briefly review recent results obtained from theoretical and experimental studies of phospholipid bilayers that clarify the relationship between lipid bilayer in-plane fluctuations (in density and composition), bending rigidity, and repulsive undulation forces. The results discussed derive from computer simulation calculations, field theory, as well as small angle neutron scattering.