Theory of hydration forces. Nonlocal electrostatic interaction of neutral surfaces

Abstract

The nonlocal electrostatic contribution to the hydration (structural) repulsion of neutral hydrophilic surfaces separated by thin water layer is considered. This contribution arises from the form of the image–charge interaction of alternating positively and negatively charged polar groups attached to one of the surfaces with nonpolar background of another surface. Characteristic features of this interaction are shown to be determined by the lateral ordering of the polar groups. Similar features were found previously in generalized free-field model of the interaction. Both models are in a good quantitative agreement with the experimental data on lipid membranes, and give consistent physical explanation to observable dependences of amplitude and decay length of the hydration force on the nature and structure of the surfaces. This similarity makes it impossible to distinguish any particular mediator of the hydration force at the present state of the knowledge. At the same time it provides a quite general picture of the role of lateral structure of the surfaces in the hydration force.