Mechanistic insights into the coupled frictional behavior of a spherical-platelet heterogeneous nanoparticle pair in PAO lubrication via molecular dynamics simulations--颗粒学报PARTICUOLOGY

Mechanistic insights into the coupled frictional behavior of a spherical-platelet heterogeneous nanoparticle pair in PAO lubrication via molecular dynamics simulations

Minseo So, Beomjoon Kim, Youngwoo Jo, Seok-Won Kang^*

Department of Automotive Engineering, Yeungnam University, 280 Daehak-ro, Gyeongsan, Gyeongbuk 38541, Republic of Korea

10.1016/j.partic.2026.02.017

Volume 111, April 2026, Pages 293-302

Received 17 November 2025, Revised 30 January 2026, Accepted 14 February 2026, Available online 6 March 2026, Version of Record 13 March 2026.

E-mail: swkang@yu.ac.kr

Highlights

• MD analysis elucidates PAO tribological behavior with TiO₂ at a MoS₂-coated interface.

• The MoS₂-coated interface sustains spherical nanoparticle rolling.

• TiO₂ alone fails to sustain rolling in PAO under sliding conditions.

• PAO–interface interactions are weaker on MoS₂ than on Fe surfaces.

• Reduced adsorption facilitates TiO₂ rolling and lowers the COF.

Abstract

In this study, atomistic molecular dynamics simulations are conducted under boundary-lubrication conditions to isolate the specific role of MoS₂ by comparing PAO 6 containing spherical TiO₂ nanoparticles with PAO 6 containing TiO₂/MoS₂ hybrid nanoparticles between Fe substrates. The simulations quantify the friction/normal forces, coefficient of friction (COF), interfacial interaction energies, and hydrocarbon number density within the adsorption layer. A single TiO₂ particle exhibits rolling during the early stage of rolling-dominated dynamics but progressively loses rolling thereafter when it cannot sufficiently displace the adjacent PAO layer. By contrast, the TiO₂/MoS₂ system sustains rolling throughout the simulation and maintains a lower COF at later stages, thus resulting in an overall 6.06% reduction in the average COF compared with the TiO₂ model. The mechanistic discriminator is interfacial adsorption: Relative to TiO₂ alone, the MoS₂-containing model shows ≈3× weaker PAO–Fe interactions, ≈32% lower interfacial PAO number density, and ≈29% fewer adsorbed chains in the interfacial layer, thus indicating reduced crowding and improved interfacial mobility. These results establish a unified view in which MoS₂ predominantly governs the interfacial separation/chemistry (adsorption moderation) while TiO₂ serves as a rolling spacer. Synergistically, they stabilize friction in PAO. Overall, this study provides mechanistic insights into friction reduction by spherical TiO₂ nanoparticles operating at MoS₂-modified metal interfaces in hydrocarbon-based lubricants, and elucidates how interfacial adsorption governs rolling persistence and, consequently, macroscopic tribological performance.

Graphical abstract

Keywords

Friction characteristics; Heterogeneous nanoparticle pair; Hydrocarbon adsorption; Molecular dynamics; Polyalphaolefin

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