Tribological properties of Langmuir-Blodgett films on silicon surface in microscale sliding contact

Microtribological properties of Langmuir - Blodgett ( LB) films transferred from behenic acid ( BehA), 2,4- heneicosanedione ( HD) and its copper complex (( HD)(2)Cu) onto silicon surface were examined. To better understand the wear resistance performance of these LB monolayers, a comparison was made with a chemically grafted octadecyltrichlorosilane ( OTS) monolayer. Auger electron spectroscopy ( AES) was used for identification of the chemical composition of the monolayers, worn areas and counterpart surfaces. We observed that the studied LB films in microscale sliding contact exhibited stable friction properties comparable to OTS, and better wear performance than OTS at high contact pressure. The tribological properties of these LB monolayers were explained in terms of molecular packing density and molecular transfer to the counterpart surface. The relationship between the wear resistance of the studied LB films and the degree of molecular packing of the surfactants indicated that the wear properties of the LB films are strongly associated with the degree of molecular packing. We suggest that the steady low friction and high wear resistance of the BehA monolayer may partly be attributed to the transfer of the amphiphilic molecules to the counterpart surface in the contact region.