RATIO OF FINAL INTERFACIAL CONCENTRATIONS IN EXCHANGE PROCESSES

In a recent paper (Dejardin, P.; et al. Langmuir, 1995, 11, 4001) final interfacial concentrations of fibrinogen and kininogen on glass were analyzed within a simple kinetic model which emphasizes that the ratio of final interfacial concentrations in a two-solute problem such as fibrinogen and kininogen (i) is independent of the type of excluded surface factor as long as this is the same for both solutes and (ii) varies linearly with the concentration of the displacer when the ratio of bulk concentrations is maintained constant. The slope is directly related to the balance for a fibrinogen molecule between the probability to be exchanged over the probability to become irreversibly adsorbed. We show in this paper that this type of linear relation could be of general validity as it is deduced from several models allowing the same kind of interpretation. We analyze the simplest one through numerical simulations of transport to the interface, as convection and/or diffusion could modify the expected foregoing result. Computation indicates departure from this behavior as a result of transport processes under static or flowing conditions in a capillary, linear variation being conserved when convection occurs but with a smaller slope due to depletion of the displacer at the interface, small curvature appearing when diffusion only occurs. In both cases we expect an underestimation of the ratio of the exchange constant over the conformation changes constant.