Molecular Simulations\nof Thermal Transport across\nIron Oxide–Hydrocarbon Interfaces

The rational design of dielectric fluids for immersion\ncooling\nof batteries requires a molecular-level understanding of the heat\nflow across the battery casing/dielectric fluid interface. Here, we\nuse nonequilibrium molecular dynamics (NEMD) simulations to quantify\nthe interfacial thermal resistance (ITR) between hematite and poly-α-olefin\n(PAO), which are representative of the outer surface of the steel\nbattery casing and a synthetic hydrocarbon dielectric fluid, respectively.\nAfter identifying the most suitable force fields to model the thermal\nproperties of the individual components, we then compared different\nsolid–liquid interaction potentials for the calculation of\nthe ITR. These potentials resulted in a wide range of ITR values (4–21\nK m<sup>2</sup> GW<sup>–1</sup>), with stronger solid–liquid\ninteractions leading to lower ITR. The increase in ITR is correlated\nwith an increase in density of the fluid layer closest to the surface.\nSince the ITR has not been experimentally measured for the hematite/PAO\ninterface, we validate the solid–liquid interaction potential\nusing the work of adhesion calculated using the dry-surface method.\nThe work of adhesion calculations from the simulations were compared\nto those derived from experimental contact angle measurements for\nPAO on steel. We find that all of the solid–liquid potentials\noverestimate the experimental work of adhesion. The experiments and\nsimulations can only be reconciled by further reducing the strength\nof the interfacial interactions. This suggests some screening of the\nsolid–liquid interactions, which may be due to the presence\nof an interfacial water layer between PAO and steel in the contact\nangle experiments. Using the solid–liquid interaction potential\nthat reproduces the experimental work of adhesion, we obtain a higher\nITR (33 K m<sup>2</sup> GW<sup>–1</sup>), suggesting inefficient\nthermal transport. The results of this study demonstrate the potential\nfor NEMD simulations to improve understanding of the nanoscale thermal\ntransport across industrially important interfaces. This study represents\nan important step toward the rational design of more effective fluids\nfor immersion cooling systems for electric vehicles and other applications\nwhere thermal management is of high importance.