A mechanism for the hydration force demonstrated in a model system

Abstract

The repulsive hydration force measured between polar surfaces originates from the strongly oriented boundary molecules in hydrogen-bonded liquids. The repulsion is due to the entropy lost (or enthalpy gained) as the surfaces approach, there being fewer configurations which are able to satisfy the boundary conditions without breaking the bond network of the fluid phase. The mechanism is illustrated by a six-vertex model for square ice which includes defects. Approximations for the bulk free energy, the net pressure and an estimate of a surface free energy are given. The calculated repulsions are exponentially decaying and of about the correct magnitude. Show more