title: AFM Studies on Liquid Superlubricity between Silica Surfaces Achieved with Surfactant Micelles.
abstract: By using atomic force microscopy (AFM), we showed that the liquid superlubricity with a superlow friction coefficient of 0.0007 can be achieved between two silica surfaces lubricated by hexadecyltrimethylammonium bromide (C16TAB) solution. There exists a critical load that the lubrication state translates from superlow friction to high friction reversibly. To analyze the superlow friction mechanism and the factors influencing the critical load, we used AFM to measure the structure of adsorbed C16TAB molecules and the normal force between two silica surfaces. Experimental results indicate that the C16TAB molecules are firmly adsorbed on the two silica surfaces by electrostatic interaction, forming cylinder-like micelles. Meanwhile, the positively charged headgroups exposed to solution produce the hydration and double layer repulsion to bear the applied load. By controlling the concentration of C16TAB solution, it is confirmed that the critical load of superlow friction is determined by the maximal normal force produced by the hydration layer. Finally, the superlow friction mechanism was proposed that the adsorbed micellar layer forms the hydration layer, making the two friction surfaces be in the repulsive region and meanwhile providing excellent fluidity without adhesion between micelles.
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Jinjin
authors.initials: J
authors.lastname: Li
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Chenhui
authors.initials: C
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Xinchun
authors.initials: X
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Weiqi
authors.initials: W
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
authors.forename: Jianbin
authors.initials: J
authors.lastname: Luo