The surface and adhesion forces between chitosan- coated mica surfaces in an acetic acid buffer solution were measured using a surface force apparatus （SFA）. The force- distance profiles were obtained under different pressure conditions. It was found that the chitosan was adsorbed on the mica surface and formed a stable nanofilm under acid conditions. The adsorbed chitosan nanofilms induced a short- range monotonically steric force when two such surfaces came close in the acid buffer. The adhesion forces between the two chitosan-coated mica surfaces varied with the loads. Strong adhesion between the two chitosan-coated mica surfaces was observed at high pressure. Such pressure-dependent adhesion properties are most likely related to the molecular configurations and hydrogen bonds reordering under high confinement.
The forces between two molecularly smooth mica surfaces are measured in monovalent and divalent cations electrolyte solutions by a surface force apparatus （SFA）. The properties of K＋, Na＋, and Mg2＋ between molecularly smooth mica surfaces are investigated. The Derjagui-Landau- Verwey-Overbeek （DLVO） force and the hydration force are detected in the experiment. The results show that in lower concentrations of a monovalent electrolyte solution （about 10-4 mol/L）, the force curves are completely in good agreement with those computed by the DLVO theory. However, additional short-range repulsive forces which deviate from the DLVO theory are observed when the concentrations of cations are above the critical bulk concentration, which is different for each electrolyte. The results show the properties of these cations on both the screening effect adsorbed on the mica surface and the hydration in solution. From the results, the interaction energy between two hydrated ions of potassium or sodium can also be estimated.
