Dependence of Adhesion Force on Withdrawal Speed in Water

We measured the adhesion force between a sphere and a plane in water using a surface force apparatus that can measure the adhesion force with ultra-high accuracy. In particular, we focused on the relationship between the withdrawal speed and the adhesion force as one of the dynamic characteristics of the surface force. PDMS (Polydimethylsiloxane) was used as a spherical probe, and PEEK (Poly Ether Ether Ketone) and Si were used as plane samples. The results revealed that the adhesion forces depended on the withdrawal speed in water. This dependence was found to be qualitatively the same as that observed in a vacuum, indicating the influence of the viscoelasticity of PDMS on the adhesion forces. Furthermore, a comparison of the adhesion forces in air and water showed that they are dependent on the combination of materials. We deduced that the wettability of the material affected the adhesion forces. Specifically, the low affinity of the two surfaces to water resulted in hydrophobic attraction, while a hydration repulsion acts when one surface becomes hydrophilic.