Interfacial Thermal Boundary Conductance and Percolation in BN and SiC Nanorod / Ethylene Glycol Nanofluids

In a working fluid loaded with ceramic nanorods, the rod–liquid interface contributes a large share of the thermal resistance. We report laboratory measurements of this interface for boron nitride (BN) and silicon carbide (SiC) nanorods dispersed in ethylene glycol (EG), and of how heat moves through the resulting suspensions. Time-domain thermoreflectance (TDTR) on model rod–liquid junctions gives a temperature-dependent thermal boundary conductance hK of 118 (BN) and 136 (SiC) MW m⁻² K⁻¹ at 300 K, rising to 172 and 198 MW m⁻² K⁻¹ at 400 K. These values lie between acoustic- and diffuse-mismatch limits. Non-equilibrium molecular dynamics (MD) gives 108 MW m⁻² K⁻¹ for BN/EG at 300 K, in agreement with TDTR within uncertainty. MD also shows a layered EG region with a 0.42 nm period near the rod surface, which is estimated to raise the local interfacial conductance by about 18 %. Spectral analysis indicates that the rod's low-frequency (2–6 THz) modes overlap the liquid's librational band. Hot-wire measurements show conductivity enhancements over EG of +30 % at 1.5 vol % and +39 % at 2.0 vol %. Above a percolation threshold φc = 2.1 vol %, the excess conductivity follows a power law with exponent t = 1.35, and the enhancement reaches +81 % at 4.0 vol %. Measured near-field radiative conductances across 2–12 nm gaps (22.5–780 W m⁻² K⁻¹) are negligible compared with interfacial conduction. In pressurised sealed cells at 240 °C, conductivity decreased by 3.0 % over 300 h, or about 1.4 % with an antioxidant additive. All values are laboratory measurements. The laboratory test programme began on 4 April 2025 at laboratories in Tokyo and Incheon; first results were obtained on 13 February 2026.