Oxide‐Mediated Formation of Chemically Stable Tungsten–Liquid Metal Mixtures for Enhanced Thermal Interfaces

Abstract

Modern microelectronics and emerging technologies such as wearable devices and soft robotics require conformable and thermally conductive thermal interface materials to improve their performance and longevity. Gallium‐based liquid metals (LMs) are promising candidates for these applications yet are limited by their moderate thermal conductivity, difficulty in surface‐spreading, and pump‐out issues. Incorporation of metallic particles into the LM can address these problems, but observed alloying processes shift the LM melting point and lead to undesirable formation of additional surface roughness. Here, these problems are addressed by introducing a mixture of tungsten microparticles dispersed within a LM matrix (LM‐W) that exhibits two‐ to threefold enhanced thermal conductivity (62 ± 2.28 W m−1 K−1 for gallium and 57 ± 2.08 W m−1 K−1 for EGaInSn at a 40% filler volume mixing ratio) and liquid‐to‐paste transition for better surface application. It is shown that the formation of a nanometer‐scale LM oxide in oxygen‐rich environments allows highly nonwetting tungsten particles to mix into LMs. Using in situ imaging and particle dipping experimentation within a focused ion beam and scanning electron microscopy system, the oxide‐assisted mechanism behind this wetting process is revealed. Furthermore, since tungsten does not undergo room‐temperature alloying with gallium, it is shown that LM‐W remains a chemically stable mixture.

Liquid Metal Composites

“…40 As illustrated in Figures 15B and 15C, after carrying out a series of analyses and experiments, researchers found that the thermal conductivity of LM is gradually enhanced with the increased volume fraction of doping different particles, including copper (Cu), Ag, Au, and carbon nanotubes. Recently, researchers proposed oxidationmediated preparation of LM-particle composites (Figure 15D), 139 which confirms that oxidation contributes to the formation of the LM particle (e.g., Ag and W [tungsten]) mixture. From the above, one can conclude that the thermal conductivity of LM composites can be effectively improved by doping particles with high thermal conductivity.…”

Solid–Liquid Composites for Soft Multifunctional Materials

“…[173][174][175] For example, tungsten can increase the thermal conductivity of LM by a factor of 3x. [176] Silver particles can also be added into eGaIn to increase electrical conductivity for printed electronics. [177] Solid particles can also modify the viscosity of LM, [178] and depending on the combination of solid and liquid particle materials chosen, the materials can alloy together forming intermetallic compounds, which can change the liquid nature of the filler into a solid or semisolid mixture.…”

A general approach to composites containing nonmetallic fillers and liquid gallium

“…Recent studies have achieved promising results on the preparation of GLM composites without a third medium or intermetallic compounds. It was found that tungsten does not form room temperature intermetallic compounds with Ga but reportedly can still be incorporated with Ga or EGaInSn by mixing in oxygen-rich environments (14). These findings suggest that there is still much to learn about GLM composites.…”