The unique properties of per- and polyfluoroalkylic substances (PFASs) in terms of chemical stability, hydrophobicity, anti-adhesion and low friction make them popular materials also in tribology. However, their high chemical stability poses serious problems owing to their accumulation in the environment and in biological systems, and regulations in this area aim to their replacement. This step is not trivial but understanding the mechanisms behind their performance may help.

Here, I will summarize our atomistic modelling studies on the chemical and physical origin of some of the properties of PFAS that are relevant in a tribological context. I will begin by discussing how PFAS can be simultaneously polar and hydrophobic [1]. Then I will focus on the study of when and why fluorinated carbon interfaces exhibit lower friction than their hydrogenated analogues [2]. Finally, I will discuss the mechanism of film transfer and solid lubrication in PTFE-lubricated steel contacts [3].

[1] L. Mayrhofer, G. Moras, N. Mulakaluri, S. Rajagopalan, P. A. Stevens, M. Moseler, Fluorine-Terminated Diamond Surfaces as Dense Dipole Lattices: The Electrostatic Origin of Polar Hydrophobicity, J. Am. Chem. Soc. 138, 4018 (2016).
[2] T. Reichenbach, L. Mayrhofer, T. Kuwahara, M. Moseler, G. Moras, Steric Effects Control Dry Friction of H- and F-Terminated Carbon Surfaces, ACS Appl. Mater. Interfaces 12, 8805 (2020).
[3] S. v. Goeldel, T. Reichenbach, F. König, Leonhard Mayrhofer, G. Moras, G. Jacobs, M. Moseler, A Combined Experimental and Atomistic Investigation of PTFE Double Transfer Film Formation and Lubrication in Rolling Point Contacts, Tribol. Lett. 69, 136 (2021).