Lattice theory of competitive binding: Influence of van der Waals interactions on molecular binding to a solid substrate and on adsorption from binary liquid mixtures
J Dudowicz, Jack F. Douglas, Karl Freed
The reversible binding of molecules to surfaces is one of the most important processes in condensed fluids, with the obvious applications in molecular separation of materials, chromatographic characterization, and material processing. Motivated in particular by the ubiquitous occurrence of binding processes in molecular biology and self-assembly, we have developed a Flory-Huggins type theory of competitive molecular binding to a solid substrate from binary mixtures of two small molecule liquids interacting by the van der Waals forces. The derived theory, in contrast to the existing theoretical frameworks, enables us to investigate the influence of van der Waals interactions on interfacial binding and selective molecular adsorption. The classic Langmuir theory of adsorption is recovered when all van der Waals interaction energies between the molecules in the bulk liquid phase and on the surface are formally set to zero. Illustrative calculations are performed for the binding of molecules to a solid surface from pure liquids and from their binary mixtures. The quantities analyzed include the surface coverage θ, the binding transition temperature Tbind, the individual surface coverages, θA and θC, and the relative surface coverages, σAC ≡ θA/θC or σCA ≡ θA/θC. The latter two quantities coincide with the degrees of adsorption directly determined from experimental adsorption measurements. The Langmuir theory is shown to apply formally under a wide range of conditions where the original enthalpies (h or hA and hC) and entropies (s or sA and sC) of the binding reactions are renormalized by the van der Waals interactions energies, in such a way that entropy-enthalpy compensation is followed, as in many experimental studies of molecular binding in mixed solvents. 2
, Douglas, J.
and Freed, K.
Lattice theory of competitive binding: Influence of van der Waals interactions on molecular binding to a solid substrate and on adsorption from binary liquid mixtures, Journal of Chemical Physics
(Accessed February 21, 2024)