Extremely low friction on gold surface with surfactant molecules induced by surface potential

Abstract

An extremely low friction state was observed on the gold surface induced by applying a specific negative potential in cationic surfactant solution. The friction force showed a remarkable reduction from 8.3 to 3.5 × 10−2 nN (reduced by 99.6%) with increasing the period of negative applied potential, and the final friction coefficient could reduce down to 3 × 10−4. The extremely low friction state was robust, and it also exhibited an excellent load bearing capacity, which cannot be damaged by a high load. Moreover, the extremely low friction state achieved under negative applied potential could keep stable even after the removal of potential, but failed in a short time, once a specific positive potential was applied. It was demonstrated that there was a stable electro-adsorption of surfactant molecules on the gold surface induced by applying a negative potential, leading to the formation of a bilayer structure on the gold surface. The hydration layers of the bilayer on the gold surface and micelles on the silica probe provided a shear plane with an extremely low shear strength, leading to the extremely low friction state on the gold surface. This study provides a method to achieve extremely low friction state by applied potential.