Effect of molecular structure of self-assembled monolayers on their tribological behaviors in nano- and microscales

The tribological behavior of self-assembled monolayers (SAMs) of ω-functional n-alkanethiol compounds were experimentally investigated at the nanoscale using friction force microscopy (FFM) and at the microscale using a microtribometer. Molecularly thin and well-ordered films of the surfactants with different terminal groups and chain length were prepared on gold substrates, gold-coated atomic force microscope (AFM) tips and steel balls by the spontaneous adsorption of the surfactant molecules. Nanoscale adhesion and friction forces between the films and gold-coated AFM tip were measured by FFM whereas microscale friction and wear properties between the films and gold-coated steel balls and uncoated steel balls were measured by the microtribometer. The nano- and microscale tribological behaviors between the films are compared and discussed in terms of the chemical structure such as terminal group and chain length of the film molecules. This investigation revealed that the molecular structure of the films significantly affects their tribological behaviors both in nano- and microscales.