DYNAMICS OF A THIN LIQUID-FILM WITH A SURFACE CHEMICAL-REACTION

The detailed description of the influence of a chemical reaction on th e dynamic behavior of a thin liquid film is of significant importance in many engineering and biological applications. In this paper, the dy namics of a thin liquid film on a solid substrate is followed until fi lm rupture or formation of local contacts. A surface chemical reaction between insoluble surfactant molecules (receptors) on the free surfac e of the film and binding sites on the solid substrate is considered. Asymptotic expansion of the equations for fluid motion with van der Wa als, capillary, and Marangoni forces leads to a model with three nonli near evolution equations describing the dynamics of the surface deform ation and the kinetics of free and bound receptors. Chemical and hydro dynamic modes are predicted and simulated numerically with different s tability regimes: for a simple linear surface reaction, the concentrat ion of receptors follows the deformation of the surface; for a nonline ar surface reaction with affinity enhanced at small distances, a clust ering of receptors is observed at the local points of contact. A compl etely new regime is also obtained where the rupture (or contact) time is delayed by several orders of magnitude, and the concentrations and film thickness may oscillate. This study could be relevant to biologic al applications where adhesion between cells and substrates can be mod eled by considering the dynamics of the thin film between them. The re sults are first compared with experiments on biological cells adhering to glass or other solid substrates where periodic patterns(wavelike m orphologies) are observed with a clustering of adhesion receptors at t he local contact points. A second possible application is the activati on of T lymphocytes, a major immunological cell type, which requires t he clustering of cell surface receptors by interaction of T-cell recep tors with surface-bound ligands. (C) 1996 Academic Press, Inc.