[26] Direct methods for measuring conformational water forces (hydration forces) between membrane and other surfaces

This chapter discusses direct methods for measuring conformational water forces between membrane and other surfaces. A number of techniques have been developed for measuring the forces among surfaces in liquids. The osmotic pressure technique allows for the measurement of repulsive forces among aligned clay sheets or lipid bilayers and various direct force measuring techniques allow for the full force laws to be measured between two surfaces. The interactions of biological surfaces can also be studied using some of these direct force-measuring techniques. The technique that has become standard in colloid science and has identified and quantified most of the fundamental interactions—such as attractive Van der Waals and repulsive double-layer forces, hydration forces, the hydrophobic interaction between two hydrocarbon surfaces in water, the steric interactions among polymer-covered surfaces, and adhesion forces—occurring among surfaces in aqueous solutions is described in the chapter. It also discusses the apparatus used to measure the forces between two lipid bilayers adsorbed on mica surfaces. Two methods are tried for adsorbing bilayers––namely, adsorption from solution and controlled deposition of two monolayers using a Langmuir–Blodgett trough.