LAUSR

Liquid metal (LM) based thermal interface materials (TIMs) have the potential to dissipate the high heat loads in modern electronics and often consist of LM microcapsules embedded in a polymer matrix. The shells of these microcapsules consist of a thin LM oxide that spontaneously forms. Unfortunately, these oxide shells degrade heat transfer between LM capsules. Thus, rupturing these oxide shells to release their LM and effectively bridge the microcapsules is critical for achieving the full potential of LM-based TIMs. While this process has been studied from an electrical perspective, such results do not fully translate to thermal applications because electrical transport requires only a single percolation path. In this work, we introduce a novel method to study the rupture mechanics of beds comprised solely of LM capsules. Specifically, by measuring the electrical and thermal resistances of capsule beds during compression, we can distinguish between the pressure at which capsule rupture initiates and the pressure at which widespread capsule rupture occurs. These pressures significantly differ and we find that the pressure for widespread rupture corresponds to a peak in thermal conductivity during compression; hence this pressure is more relevant to LM thermal applications. Next we quantify the rupture pressure dependence on LM capsule age, size distribution, and oxide shell chemical treatment. Our results show that large freshly prepared capsules yield higher thermal conductivities and rupture more easily. We also show that chemically treating the oxide shell further facilitates rupture and increases thermal conductivity. We achieve a thermal conductivity of 16 Wm-1K-1 at a pressure below 0.2 MPa for capsules treated with dodecanethiol and hydrochloric acid. Importantly, this pressure is well within the acceptable range for TIM applications.