RATIO OF FINAL INTERFACIAL CONCENTRATIONS IN EXCHANGE PROCESSES

In a recent paper (Dejardin, P.; et al. Langmuir, 1995, 11, 4001) fina l interfacial concentrations of fibrinogen and kininogen on glass were analyzed within a simple kinetic model which emphasizes that the rati o of final interfacial concentrations in a two-solute problem such as fibrinogen and kininogen (i) is independent of the type of excluded su rface factor as long as this is the same for both solutes and (ii) var ies linearly with the concentration of the displacer when the ratio of bulk concentrations is maintained constant. The slope is directly rel ated 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 ge neral 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 diffus ion 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 co nserved when convection occurs but with a smaller slope due to depleti on of the displacer at the interface, small curvature appearing when d iffusion only occurs. In both cases we expect an underestimation of th e ratio of the exchange constant over the conformation changes constan t.