Adhesion force between particles and substrate in a humid atmosphere studied by atomic force microscopy

Using an atomic force microscope (AFM), adhesion forces between glass particles or AFM tips and hydrophilic or hydrophobic substrates were measured as a function of relative humidity (RH). The observed adhesion force between the glass particles and the hydrophilic substrate increased with RH due to strong capillary condensation. In contrast, the adhesion force between the glass particles and the hydrophobic substrate was found to be almost constant for all RHs, due to weak capillary condensation. The adhesion force between an AFM tip and a mica plate had a maximum value at a certain RH. This can be evaluated by calculating with consideration for the tip shape. On the other hand, the adhesion force for a silica plate increased drastically over a certain RH and could be explained due to the surface roughness of the silica plate. The presence of nanometer-scale roughness can play a critical role in the absolute value of the adhesion force between an AFM tip and the substrate in a humid atmosphere.