Structure regulation of nano-SiO₂ microcapsules and synergistic lubricating effect with PTFE in epoxy resin coating

In this study, hollow microporous silica nanospheres (HMS) with tunable particle size and hollow structure were synthesized by adjusting the ethanol-water ratio during hydrolysis and polycondensation. Results demonstrate that the HMS prepared at an ethanol-water ratio of 1:1.7 feature uniform spherical morphology, a diameter of 500–600 nm, high hollow ratio and an PAO6 loading capacity of 30 wt%. Furthermore, self-lubricating epoxy resin (EP) coatings modified with PAO6-laden HMS microcapsules (PSMS) and PTFE were fabricated by spin-coating to explore solid-liquid synergistic lubrication. Under a load of 20 N and a reciprocating frequency of 2 Hz, systematic tribological tests were conducted.15 wt% PSMS@EP coating has a friction coefficient (COF) of 0.042 and wear rate of 1.19 × 10 −6 mm 3 /Nm. When PSMS and PTFE are blended at a mass ratio of 1:1 with the total filler loading fixed at 15 wt%, the average COF of the EP coating is further reduced to 0.033, and the coating exhibits excellent load adaptability. Lubrication mechanism analysis reveals that friction and compression induce the sustained release of lubricating oil inside PSMS, which forms an interfacial oil film to suppress the adhesion of poorly bonded wear debris and maintain long-term lubrication. Meanwhile, PTFE forms a solid transfer film on steel balls via physical adsorption and tribochemical reactions. The liquid oil film and PTFE transfer film construct a stable solid-liquid coupled lubricating system reinforced by trace silica. Their synergistic effect converts direct friction between EP and steel counterpart into low-resistance interlayer shearing, enabling reliable long-term tribological protection.