Relating friction and adhesion for single smooth contact by means of models and experiments

The relation between adhesion and the friction force measurements for a single smooth contact has been studied by means of sliding and pull-off experiments in ambient as well as under high vacuum (HV) conditions. The experimental results have been analysed in several ways using contact models. First, it is shown how the appropriate adhesion regime can be determined based on the analysis of Maugis–Dugdale (M–D). Further, a modified M–D model incorporating meniscus forces are discussed. This model is able to calculate the contact radius for cases where meniscus forces due to the presence of water are dominating. The approach will be illustrated by means of adhesion and friction force measurements between a silicon ball and a glass flat surface (Si–glass interface) performed on a novel designed vacuum based adhesion and friction tester. Under HV conditions, meniscus forces are not dominating and only van der Waals interactions are present. Combining the models with the measured adhesion and friction force data, the work of adhesion and the shear stress present between the Si–glass interface can be determined. According to the theory, the extent of the adhesive zone increases with an increase in the relative humidity (RH). When comparing HV conditions with ambient conditions, it has been found that the adhesion as well as friction force is significantly lower under high vacuum conditions for the Si–glass interface. When comparing modelling results with experiments, it can be concluded that the trends from theoretical predictions are in good agreement with the measurements, both for the HV and ambient regime.