Systematic study of the effect of disorder on nanotribology of self-assembled monolayers

M. Chandross, E. B. Webb III, M. J. Stevens, G. S. Grest, and S. H. Garofalini, Phys Rev Lett, 93, 166103/1-4 (2004).

The adhesion and friction between pairs of ordered and disordered self-assembled monolayers on SiO2 are studied using molecular dynamics. The disorder is introduced by randomly removing chains from a well ordered crystalline substrate and by attaching chains to an amorphous substrate. The adhesion force between monolayers at a given separation increases monotonically with chain length at full coverage and with coverage for fixed chain length. Friction simulations are performed at shear velocities between 0.02-2 m/s at constant applied pressures between 200 and 600 MPa. Stick-slip motion is observed at full coverage but disappears with disorder. With random defects, the friction becomes insensitive to chain length, defect density, and substrate.

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