Calculation of the interaction energy between two parallel adsorbing planes immersed in a solution composed of molecules of different size

Abstract

The interaction between parallel planes, immersed in a solution from which r-mer molecules are adsorbed, is treated theoretically using the multilayer lattice model for adsorption from solution. The surface excess of the configurational free energy is calculated as a function of the plane separation. The model is applicable both in dilute and concentrated solutions. Results are presented for solutions composed of monomers plus dimers and monomers plus flexible tetramers. The influence of the following parameters is shown: strength of adsorption, segment interchange energy, and concentration of the solution.

Adsorption of r-mers with one end-segment preferentially adsorbed leads to a repulsive energy between the parallel planes at small separations. An increase in the length of the r-mer or in the quantity of r-mer adsorbed increases the repulsive energy at any separation.

Adsorption of r-mers with every segment preferentially adsorbed from solution gives an attractive energy which increases as the planes approach.