ABSTRACT
Self-assembled monolayers (SAMs), formed by chemical adsorption of surfactant molecules on solid surfaces, can be used as boundary lubricants. The grafting of monolayers on a rigid substrate allows to control the surface chemistry and consequently the surface energy and reactivity without varying the roughness and the mechanical properties. The objective of this work was to illustrate the inuence of the nature of interfacial interactions on the sliding friction of polymers. Two different substrates were used: a hydrophilic substrate (hydroxylated silicon wafer) and a hydrophobic one (silicon wafer grafted with a CH3 terminated silane). Both substrates exhibit identical stiffness and roughness and differ only by their surface chemistry. Friction of model elastomers (crosslinked poly(dimethylsiloxane), PDMS) against both types of substrates was quantied, by using a translation tribometer for different normal forces and friction speeds. Experimental results indicate that the friction coefcients of PDMS against hydrophilic and hydrophobic substrates are different for low friction speed (with a greater friction coefcient for hydrophilic wafer). However, at higher speed, friction coefcients obtained with both types of substrates become identical. This work evidences the complex competition between interfacial interactions and polymer surface rheological behaviour.
