Relationship between layered structure and wear behavior of concentrated polymer brushes

Concentrated polymer brushes (CPBs)—super-low-friction polymeric coatings composed of densely grafted polymer chains on a solid substrate—hold great promise for use in mechanical tribological components such as bearings and seals. However, their durability must be further improved before they can be deployed across a wide range of tribological applications. This study investigated the relationship between the wear mechanisms of poly(methyl methacrylate)-CPBs (PMMA-CPBs) and their layered structure, which comprises dilute, middle, and concentrated layers. Using a custom-built surface force apparatus, we examined the influence of the counterface bearing steel material's relative vertical position on the wear process, particularly focusing on the role of the dilute layer in lubrication film formation. The results showed that thickening of the dilute layer during sliding contributes to the formation of the lubrication film, which reduces the wear rate of the PMMA-CPB. Furthermore, the wear volume of the PMMA-CPB was found to be proportional to the characteristic quantity δ 1/2 L , where δ is the indentation depth and L is the sliding distance, based on a modified version of Archard's wear model tailored for this study. The findings suggest that improving the durability of PMMA-CPBs can be achieved by controlling the layer structure, such as thickening the dilute layer to reduce indentation depth and increasing the hardness of the concentrated layer. These insights offer crucial design guidelines for enhancing the durability of PMMA-CPBs in tribological applications. • The wear behavior of PMMA-CPBs is governed by their layered structure under applied loads. • Friction causes thickening of the dilute layer and thinning of the concentrated layer. • The dilute layer induces vertical lift, forming a lubrication film that reduces wear. • A modified Archard’s wear model shows that indentation depth controls wear behavior. • Enhancing the dilute layer thickness and concentrated layer hardness improves durability.