Abstract
We have investigated the thermal fluctuations of giant unilamellar dimyristoylphosphatidlycholine vesicles in the presence of both non-ionic and ionic surfactants (peptides) with identical apolar chains. Using vesicle fluctuation analysis, the effects of ionic and non-ionic surfactants upon membrane bending rigidity in the case of no added salt have been determined and the electrostatic contribution thereby isolated. We interpret these experimental findings in terms of a mean-field free-energy model for the adsorption of charged surfactants to a lipid bilayer and couple these results to describe the electrostatic contribution to membrane bending rigidity. This experimental study demonstrates how electrostatics affect the elastic properties of unilamellar bilayers.