Viscoelastic relaxation of bilayer lipid membranes. Frequency-dependent tension and membrane viscosity

Photon correlation spectroscopy has been used to study capillary waves on black lipid membranes of glycerol monooleate at temperatures above the lipid transition. For the first time the tension and viscosity of solvent-free bilayers have been observed to display a frequency dependence. The variations of both parameters can be accounted for by a Maxwell viscoelastic fluid model having a relaxation time of 37 microseconds. The equilibrium (omega = 0) tension is compatible with literature values. The present results do not suffice to precisely define the specific molecular processes involved, but relaxation times similar to the present are associated with certain phenomena in phospholipid vesicles. Bilayers containing hydrocarbon solvent do not show such relaxation, presumably due to their weaker intermolecular interactions.