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 µm 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.

Molecular Orientation, Crystallinity, and Topographical Changes in Sliding and their Frictional Effects for UHMWPE Film

“…The cleaning and coating procedures are provided in Ref. [3,26]. The thickness of the UHMWPE film used in this study was 12.3 lm and its initial roughness (R a ) was 0.56 lm, measured within a scan area of 10 lm 9 10 lm using an AFM.…”

“…The setup has been described in detail elsewhere [3,26]. A cleaned silicon nitride ball 4 mm in diameter with a surface roughness of 5 nm (as provided by the supplier) was used as the stationary counterface.…”

“…The molecular orientation of PTFE has been widely studied by Tabor's and Tanaka's groups [24,25] in 1970s in which they showed the polymer molecule orientation along the sliding direction. Recently, we have studied UHMWPE as a thin film and investigated its friction and wear properties on different substrates, different thicknesses, and different surface energies using continuous sliding tests [2,3,26]. Our studies have shown that the crystallinity and molecular orientation of the polymer changes as the sliding progresses in one direction.…”

Tribological Properties of Ultra-Thin Functionalized Polyethylene Film Chemisorbed on Si with an Intermediate Benzophenone Layer

“…In recent studies, many polymer films on Si substrate have shown low friction and high wear performance [12][13][14][15]. In our previous studies, we have applied different surface modification techniques to ultra high-molecular-weight polyethylene (UHMWPE) film and extended the wear durability by several orders [16][17][18], showing that polymer films are very promising coating materials in lowering friction and improving wear durability of Si substrate. However, for the application of such coatings in micro/nanodevices such as MEMS (microelectro-mechanical systems), it is also important that the thickness of the coating is controlled and brought down to only few nanometers.…”

TRIBOLOGY OF UHMWPE THIN FILMS ON Si WITH INTERFACIAL LAYERS AND MODIFICATIONS

“…The critical load as a function of different interfaces; and the scratching velocity is 0.1 mm/s and the scratch length is 1 cm 33. …”