FLOCCULATION BEHAVIOR OF EGG PHOSPHATIDYLCHOLINE LIPOSOMES CAUSED BY CA2+ IONS

The interaction between bilayer phospholipid membranes has been studie d through flocculation phenomena of phospholipid liposomes. Unlike lip osomes composed of other phospholipids, liposomes made of egg phosphat idylcholine (PC) have a strong resistance against aggregation. This ph enomenon can be attributed to the hygroscopic nature of the choline gr oup, i.e. the repulsion force that is the so-called ''hydration force' ' or the ''steric force'' with hydration is the origin of the phenomen on. By changing the diameter of the PC liposomes, we observed a differ ent flocculation behavior of the liposomes when the electrostatic surf ace potential of the liposomes is zero. For diameters above 320 nm, a weak flocculation occurred, but liposomes with diameters below 200 nm are stable as colloidal dispersions. This diameter dependency of flocc ulation has been explained by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory together with hydration forces.