Spectral Investigation of Thermal Conductance at Solid/Fluid Interfaces

Escalating transistor densities are forcing power‐device hotspots above 1 kW cm⁻², a regime where the interfacial thermal conductance, rather than bulk boiling or convection conductance, bottlenecks two-phase cooling performance. The heat flux across a solid/liquid (SL) boundary is limited by the interfacial thermal conductance G, which in turn depends on how the solid lattice and the adjacent nanoscale liquid layers exchange energy. Spectral analysis (i.e., the study of atomic vibrations of interfacial atoms) has been utilised to analyse energy exchange for solid/solid interfaces, it has not yet been applied comprehensively to solid/liquid interfaces. The vibrational density of states (VDOS) is a popular spectral metric used to quantify thermal transport but has physical limitations and lacks generalisability.

We use high-fidelity molecular-dynamics (MD) simulations along with spectral analysis to examine three progressively more realistic systems: (a) a simple Lennard-Jones (LJ) SL interface, (b) the same LJ interface confined by a nanochannel that incorporates a liquid meniscus, and (c) metal/water interfaces whose wettability can be tuned by surface chemistry. In all three cases, the VDOS does not track the observed variation in G. In case a) our novel spectral metrics help us discover that the familiar exponential-to-linear crossover of G with surface wettability marks the point where the interfacial liquid solidifies, in contrast to previous hypotheses [1]. Introducing a meniscus in b) is shown to boost G at all wettabilities: our analysis reveals that the gradual increase at modest wettabilities originates from stronger out-of-plane vibrational coupling, whereas an abrupt jump on highly wetting walls is driven by newly activated in-plane modes [2]. Finally, for realistic metal/water interfaces we show that changes in G with wettability stem from how efficiently each metal utilises its own spectrum, while differences between metals reflect variations in mode-utilisation efficiency [3].

These spectral insights hint at simple design rules to resolve interfacial heat-transfer bottlenecks, such as promoting in-plane mode utilisation through hydrophilic coatings or exploiting nanoconfined menisci. Our results therefore are relevant to rationally engineered thermal interfaces for next-generation electronics, plasmonic devices and other high-heat-flux technologies.

References

[1] A. El-Rifai, S. Perumanath, M. K. Borg, and R. Pillai. Unraveling the Regimes of Interfacial Thermal Conductance at a Solid/Liquid Interface. J. Phys. Chem. C, 128, pp. 8408–8417, 2024.

[2] A. El-Rifai, L. Klochko, S. Perumanath, D. Lacroix, R. Pillai, and M. Isaiev. Spectral Mechanisms of Solid/Liquid Interfacial Heat Transfer in the Presence of a Meniscus. Phys. Chem. Chem. Phys., 27, 10185-10197, 2025.

[3] A. El-Rifai, S. Perumanath, and R. Pillai. Spectral Analysis of Thermal Conductance at Metal/Water Interfaces (in preparation).