Enhanced Adsorption of Epoxy-Functional Nanoparticles onto Stainless Steel Significantly Reduces Friction in Tribological Studies

Epoxy-functional sterically-stabilized diblock copolymer nanoparticles (~27 nm) are prepared via RAFT dispersion polymerization in mineral oil. Nanoparticle adsorption onto stainless steel is examined using a quartz crystal microbalance. Incorporating epoxy groups within the steric stabilizer chains results in a near two-fold increase in the adsorbed amount, Γ, at 20 °C (7.6 mg m-2) compared to epoxy-core functional nanoparticles (3.7 mg m-2) or non-functional nanoparticles (3.8 mg m-2). A larger difference in Γ is observed at 40 °C; this suggests chemical adsorption of the nanoparticles rather than merely physical adsorption. A remarkable near five-fold increase in Γ is observed for larger (~50 nm) epoxy-functional nanoparticles compared to non-functional nanoparticles (31.3 vs. 6.4 mg m-2, respectively). Tribological studies conducted at 60-120 °C confirm that the adsorption of epoxy-functional nanoparticles leads to a significant reduction in the friction coefficient.