Relative humidity is not a direct factor to influence adhesion force between two silica surfaces

The dependence of adhesion force on relative humidity (RH) is ambiguous and demands clarification. The adhesion force behaviors between two silica surfaces were investigated with the continuous change of RH on an atomic force microscope. Results show that the variation of adhesion force is directly related to water-thin film and chemical properties of surfaces, instead of RH itself. With the continuous change of RH in a short duration, the adhesion force usually changes slightly without a characteristic trend. However, with a long duration at a new RH, the force magnitude can ultimately be changed effectively due to the variation of water-thin film thickness and chemical properties of surfaces. Especially, with a low new RH for some time, the adhesion force can become unusually large due to the bond-rupture of siloxane bonds. The unusually large force lasts for some time with the constant low RH, and then suddenly drops to a small force. Therefore, the duration at a new desired RH does matter in the investigation of RH dependence of adhesion force. The results may be useful for the investigation of the RH dependence and the anti-adhesion design of small-scale components.