ABSTRACT
Hydration forces, now known to dominate the interaction of all phospholipid membranes as they approach within 10 to 20 Å, remained unrecognized until relatively recent times. This is surprising, because the phospholipids that merge their hydrocarbon tails create bilayers covered with a phalanx of polar groups that must hold on to the solvent into which they would otherwise dissolve. The tenacity of holding this water is part of a natural tension in amphiphilic aggregates, a balance between the high energy of a hydrocarbon/water interface and the energy lowering adsorption of solvent. That water costs energy to remove. So, when two such surfaces come together, that cost translates into a strong force of repulsion. It has now been recognized as the dominant force between all hydrophilic surfaces.
