Mariño, FátimaGiner-Rajala, ÓscarLópez Iglesias, EnriquetaAmigo Pombo, Alfredo JoséFernández Pérez, Josefa2025-06-242025-06-242025-05-14Applied Surface Science Volume 706, 15 October 2025, 163528https://hdl.handle.net/10347/42323This study aims to examine the effect of particle size on stability and tribological performance of two iron oxide nanoparticles (Fe3O4 NPs), with diameters of 14 and 19 nm respectively, modified with octadecyltrichlorosilane, OTS, as lubricant additive in a polyalphaolefin (PAO6) at three concentrations (0.007, 0.015, 0.030 wt%). From the temporal evolution of the refractive index, it can be inferred that the stability times of the nanodispersions containing silanized nanoparticles are longer than those of their uncoated counterparts, increasing with NPs size. The optimal concentration for both nanoparticle sizes was 0.015 wt%. The PAO6 + 0.015 wt% Fe3O4-OTS (19 nm) nanodispersion led to wear reductions of up to 59 % (longitudinal sectional area), compared to that of PAO6. The tribological mechanism likely involves the formation of a tribofilm and the mending effect. Measurements of density and three transport properties of nanolubricants at the optimum concentration show no significant variation compared to those of PAO6.eng© 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by- nc-nd/4.0/ ).Attribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/e-transmission fluidNanoadditiveTribological mechanismFunctionalizationNanoparticle coatingjournal article10.1016/j.apsusc.2025.1635281873-5584open access