Swelling of bilayer lipid membranes

Short-range repulsive (''hydration'') forces dominate the interactions of many bilayer membranes, as they approach a close contact, and play an important role in the membrane swelling. The physical origin of these forces has still not been completely understood, especially for ionic bilayers. This study presents an extension of the osmotic stress method for evaluation of the bilayer membrane swelling in humid environment. Zwitterionic dimyristoylphosphocholine (DMPC) and ionic dioctadecyldimethylammonium bromide (DODAB) multilayers are studied by means of low-angle X-ray diffraction and Fourier transform infrared spectroscopy. The effect of humidity on the swelling and organization of the DMPC and DODAB multilayers is compared. The physical origin of the established strong short-range repulsive forces in both lipid systems is discussed.