Lubrication with Oil-Compatible Polymer Brushes

Abstract

A polymer-brush-based, surface-modification strategy for friction and wear reduction in hard contact under boundary-lubrication conditions is proposed, specifically for a non-aqueous environment. Surface-initiated atom-transfer radical polymerization was employed for the synthesis of three different oil-compatible, hydrophobic polymer brushes based on alkyl methacrylates. This study presents polymerization kinetics, chemical characterization by means of Fourier-transform infrared spectroscopy and surface morphologies observed in atomic force microscopy. The lubrication properties of the anchored polymers were evaluated macroscopically by means of ball-on-disk methods and on the nanonewton scale by lateral force microscopy and showed significant reduction in friction up to contact pressures as high as 460 MPa. The frictional response of surface-grafted polymers is shown to depend strongly on the compatibility of the polymer with the chosen lubricating fluid.

Friction Modifier Additives

“…One solution is to grow polymers on surfaces by polymerization from initiators pre-attached the surface, socalled "grafting-from". Very dense polymer films can be formed in this way and these show low friction in both high and low speed conditions [199,200]. Unfortunately this approach does not provide the replenishment process generally required of lubricant additives and is thus a surface treatment rather than being delivered and maintained by the lubricant.…”

Challenges and developments of self-assembled monolayers and polymer brushes as a green lubrication solution for tribological applications

“…121 The pioneers of polymer brushes for tribology, Klein et al, also realised the importance of a good solvent to facilitate swelling and therefore better sliding performance. 278 The immersion of polymer brushes in good solvent allows brush swelling, known to help lubricate as illustrated in Fig.…”

“…Hence, in addition to SAMs, it is also a useful technique in measuring polymer brushes, see details later. 121,122,144 Since ellipsometry needs a model to t the raw data and normally does not take into account of surface roughness, small errors may be included in the thickness measurements. Ellipsometry is also used for investigating oxide thicknesses on silicon substrates.…”

Salt Dependence of the Tribological Properties of a Surface-Grafted Weak Polycation in Aqueous Solution

“…However, there are other routes to increase friction where stiff surfaces are required [3]. When lubrication is necessary, grafting polymers on surfaces may be applied for both oil-based [4][5][6] and aqueous [6][7][8][9] environments. Such grafted polymers are known as brushes [10] and are often used for modifying surfaces to improve material compatibility, to prevent aggregation (steric stabilization), or to add functionality.…”