Effects of interfacial energy modifications on the tribology of UHMWPE coated Si

Abstract

This paper presents results on the tribological properties of ultra-high molecular weight polyethylene (UHMWPE) films on Si substrates modified by interfacial layers of different surface energies (hydrophobicity). Five different interfaces, namely bare Si (i.e. no interfacial modification), heated Si, Si/3-aminopropyltrimethoxysilane (Si/APTMS), hydrogenated Si (Si-H) and Si/octadecyltrichlorosilane (Si/OTS) were prepared on a Si substrate by physical and chemical methods that gave water contact angles of the interfaces as 21°, 46°, 52°, 71° and 104°, respectively. UHMWPE (6 νm thickness) was coated onto surface energy modified Si substrates by the dip-coating method. The tribological tests were conducted using a ball-on-disc tribometer with a 4 mm diameter silicon nitride ball as the slider. Bare Si, which was the most hydrophilic of all, and Si/OTS, the most hydrophobic interface, showed much lower wear resistance when compared with heated Si, Si/APTMS and Si-H interfaces, with Si-H interface giving the best result. The results of a scratch test for adhesion strength between the interface and UHMWPE were consistent with the tribological properties of the films. It is concluded that the wear performance of ultra-thin UHMWPE films on Si substrates could be extended by several orders of magnitude by suitably modifying the interfaces (different surface energies) of the silicon substrates. The coefficient of friction also follows a similar trend with Si-H interface giving the lowest value among all samples. © 2008 IOP Publishing Ltd.