Study on microscale adhesion between solid surfaces with scanning probe

The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments. The adhesion forces between a flat tip with a diameter ～1.7 μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope (AFM). The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces. The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface. The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy. The adhesion measurements were carried out under ambient conditions, in a nitrogen-filled glove box, under distilled water, and under potassium chloride (KCl) solution. The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area. The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization, measurement methods and the environment. Under different environments, there are different interactions and factors affecting the adhesion force, and the dominant interactions and factors may be different too. The various interactions and factors are mutually coupled to determine the final adhesion force.