The tribological performance of the R1233zd refrigerant in extreme confinement between two hematite $${\text{Fe}}_{ 2} {\text{O}}_{ 3} \left( {01\overline{1} 2} \right)$$ surfaces is studied thanks to large-scale molecular dynamics simulations based on a force field previously parametrized from ab initio calculations. With atomically smooth surfaces, and a refrigerant film thickness as small as 2 nm, adsorbed layers of R1233zd molecules on $${\text{Fe}}_{ 2} {\text{O}}_{ 3}$$ surfaces resist to high pressures and high sliding velocities. In ultra-confined systems, friction behaves non-monotonously, reaching a global maximum when a single saturated layer is formed. Moreover, sliding simulations with a rough surface reveal total film breakdown for a local pressure around 13 GPa. Interestingly, the addition of a sliding velocity enhances the performance through a hydrodynamic lift-like mechanism: the higher the sliding, the higher the chance for refrigerant molecules to be entrained into the asperity contact.

The adsorption phenomenon of refrigerant R-1233zd(E) molecules on a hematite Fe2O3(011 (1) over bar2) surface is studied at the quantum level thanks to density functional theory + U (DFT + U) calculations employing a van der Waals functional combined with a spin-polarized system. The results show different adsorption sites on the solid surface depending on orientations of the molecule, characterizing strong interactions between the refrigerant molecule and both iron and oxygen atoms. A range of binding energy values of -0.92 to -0.22 eV is observed. These ab initio results are used to parametrize a force field at the refrigeranthematite interface for larger scale molecular dynamics simulations. Effects of these ab initio considerations on density and velocity profiles are studied, in the case of a confined fluid between two surfaces as in a lubricated contact. The high binding energy values induce a locking effect of the R-1233zd(E) molecules close to the hematite surface, showing a resistance to compression (P-z = 500 MPa) and shearing (v(s) = 20 m/s).