Potential-Dependent Friction On A Graphitic Surface In Ionic Solution

Applied potential can control the friction on electrical conductor surfaces in both air and liquid environments. Using a three-electrode electrochemical cell filled with aqueous ionic solution under atomic force microscopy, a potential-dependent friction phenomenon was observed on a graphitic surface. With an applied positive potential on the graphitic surface, the friction force increased over that observed under neutral applied potential and increased with increasing positive potential. With the applied negative potential on the graphitic surface, lubricity was observed compared to the case with the neutral potential on the graphitic surface. The applied potential also changed the interaction force between the probe and graphitic surface, where the positive potential resulted in a stronger attractive force, while the negative potential induced a stronger repulsive force. The mechanism of the friction and interaction force modulation under the applied potential was ascribed to the rearrangement of hydrated cations and anions on the graphitic surface under different potentials, resulting in electrostatic forces and hydrogen bonds varying as a function of potential. This study demonstrates that the friction on a graphitic surface can be modulated by the surface potential in aqueous ionic solutions, which may provide a novel method for reducing friction in aqueous environments.