For decades, researchers have known that a voltage applied between two objects can increase their mutual stickiness — an effect called electroadhesion that has modern applications to robotic gripping. However, while theoretical treatments of the problem have considered the roughness of the two surfaces, they have neglected the detailed mechanics at play when the objects come into contact. There has also been disagreement over the precise relationship between the adhesive force and the magnitude of the voltage.

In The Journal of Chemical Physics, a researcher offers a mean-field approach to the problem, keeping track of the effect that the applied voltage has on the contact between two elastic surfaces. The theory suggests that an applied voltage draws rough surfaces toward one another, decreasing the gaps between their craggy faces and further concentrating the electric field between them. This, in turn, draws the surfaces even closer together.

The work builds on the author’s prior theoretical contributions to contact mechanics, which provides a way to calculate the average separation and the distribution of separations between two surfaces given a small pressure holding them together. An applied voltage serves to increase the effective pressure — and thus the friction — between two surfaces.

Numerical results, calculated for insulating surfaces of random roughness, indicate there is a critical voltage past which small increases can lead to relatively large decreases in surface separation and increases in the friction between surfaces. The author suggests that in addition to being relevant for studies of robotic gripping, the work may also aid in studying the interface between fingers and touchscreens.

Source: “The dependency of adhesion and friction on electrostatic attraction,” by B. N. J. Persson, The Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5024038.