la6b01237_si_001.pdf (1.62 MB)
AFM Studies on Liquid Superlubricity between Silica Surfaces Achieved with Surfactant Micelles
journal contribution
posted on 2016-05-18, 00:00 authored by Jinjin Li, Chenhui Zhang, Peng Cheng, Xinchun Chen, Weiqi Wang, Jianbin LuoBy
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.