Gallium-based liquid metal alloy incorporating oxide-free copper nanoparticle clusters for high-performance thermal interface materials

•An oxide-free copper nanoparticle incorporation method was developed for gallium-based liquid metal matrix.•Liquid metal-copper nanoparticles composite shows ~180% enhancement of thermal conductivity compared to the untreated one.•The thermal percolation effect was investigated by a clustering model with a visualization test.•A high-quality interface between the liquid metal composite and a silicon substrate is demonstrated by X-ray photoelectron spectroscopy.•~20% lower junction temperature was shown compared to thermal grease with excellent thermal stability at high heat flux regime.