The mean bending modulus of bilayer is difficult to be measured directly in experiment but found relating to its bending rigidity. In this paper, the size of entropic stabilized vesicles, which were prepared by freeze-thaw cycle method, was investigated. It is observed that the diameters of these freeze-thaw vesicles decrease sharply and then gradually increase with salt concentration of hydration solution increasing. However, the sizes remain unchanging in the range of higher salt concentration when the charged component 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DOPG) is added in membranes. While the Zeta potential of membranes with various compositions presents the same trend of first rapid decreasing then to be steady. On the other hand, the size of multi-lamellar vesicles, prepared by hydration directly, keeps in a constant after quick decrease as salt concentration increasing. The results indicate that the electrostatic screening and properties of electrostatic double layer of the lipid bilayer are the dominant factor in low and high salt concentrations, respectively. The structure of lipid molecules and the membrane fluctuation of multi-lamellar vesicle would influence the properties of the electrostatic double layer in high salt concentration.

Key words: multi-component charged lipid membrane, freeze-thaw method, zeta potential, bending rigidity, electrostatic screening, electrostatic double layer