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This is probably the first study about the drainage of curved liquid films in the presence of colloidal particles. The systems did not contain any surfactant. In the presence of monodispersed colloidal particles, thinning occurs in a stepwise manner (stratification). It has been shown that the size of the film is an important parameter in the stepwise thinning process. This investigation found a critical film size below which at least one layer of particles stays in the film at equilibrium; a "spot" (a thinner section of the film), even if formed, does not expand and is in equilibrium with the film. The area of the spot expands linearly with time. The rate of spot-area expansion increases linearly with the film perimeter and can be increased or decreased merely by changing the film size. The stepwise film thinning and the effects of film size and particle concentration on film stability are discussed on the basis of the diffusive-osmotic mechanism.

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The specific interaction between a model biomolecular pair, cholera toxin B oligomer (CTB) versus its receptor ganglioside GM1, was investigated using an atomic force microscope. Force versus separation curves in approach/retraction cycles between a GM1-coated tip and CTB were collected. On the basis of a statistically significant number of force curves measured at different points on the sample surface, attractive forces during retraction were frequently observed. As confirmed by the results of control experiments, the attractive force was correlated to the rupture force of the CTB-GM1 specific bond, a quantitative measure of the specific interaction. Using a GM1-coated tip, force maps were generated on the CTB-containing surface to illustrate the CTB distribution. By varying the approach/retraction rate at 0.5, 1.0, and 3.0 Hz, the mean adhesive forces of 0.49, 0.17, and 0.03 nN were measured. It allows the quantification of the characteristic interaction time needed for strong CTB-GM1 binding in the range of 7-20 ms when CTB and GM1 were separated at a distance shorter than 10 nm. A shorter interaction time dramatically decreased the strength of the binding. We also observed a strong influence of the ionic strength on the binding time. The specific bond formation was significantly delayed in the presence of electrolyte in the media. This is ascribed to the influence of the ionic strength on both long-range and short-range interactions.