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.

The formation of frost and ice can have negative impacts on travel and a variety of industrial processes and is typically addressed by dispensing antifreeze substances such as salts and glycols. Despite the popularity of this anti-icing approach, some of the intricate underlying physical mechanisms are just being unraveled. For example, recent studies have shown that in addition to suppressing ice formation within its own volume, an individual salt saturated water microdroplet forms a region of inhibited condensation and condensation frosting (RIC) in its surrounding area. This occurs because salt saturated water, like most antifreeze substances, is hygroscopic and has water vapor pressure at its surface lower than water saturation pressure at the substrate. Here, we demonstrate that for macroscopic drops of propylene glycol and salt saturated water, the absolute RIC size can remain essentially unchanged for several hours. Utilizing this observation, we demonstrate that frost formation can be completely inhibited in-between microscopic and macroscopic arrays of propylene glycol and salt saturated water drops with spacing (S) smaller than twice the radius of the RIC (δ). Furthermore, by characterizing condensation frosting dynamics around various hygroscopic drop arrays, we demonstrate that they can delay complete frosting over of the samples 1.6 to 10 times longer than films of the liquids with equivalent volume. The significant delay in onset of ice nucleation achieved by dispensing propylene glycol in drops rather than in films is likely due to uniform dilution of the drops driven by thermocapillary flow. This transport mode is absent in the films, leading to faster dilution, and with that facilitated homogeneous nucleation, near the liquid-air interface.

Liquid metal (LM)-based thermal interface materials (TIMs) have the potential to dissipate 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 forms spontaneously. 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 composed 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 W m −1 K −1 at a pressure below 0.2 MPa for capsules treated with dodecanethiol and hydrochloric acid. Importantly, this pressure is within the acceptable range for TIM applications.

typically boost the thermal conductivity of the overall composite an order of magnitude beyond the base polymer (i.e., k ≈ 0.2 W m -1 K -1 for polymers). [5] Unlike curing TIMs, which exhibit elastomeric qualities due to cross-linking, noncuring TIMs can be dispensed, reworked, and remain in a fluid-like state under thermal cycling. The application-space for TIMs is large with varying requirements for mechancial, thermal, and other properties. For a detailed perspective on TIMs, we refer the reader to a number of review articles. [1,[5][6][7] Commercially available TIMs show modest thermal conductivity values that typically only range from 0.5-3 W m -1 K -1 despite containing high conductivity additives. [6] The relatively poor thermal transport through TIMs stem from a number of factors including interior thermal interface resistance between the polymer and filler particles, interior thermal interface resistance at filler-filler interfaces, and exterior thermal contact resistance to the TIM. [1,5,6] Increasing the filler volume fraction increases thermal conductivity, but is also subject to practical limitations as this reduces mechanical deformability and increases stiffness. Thermal transport percolation is achieved at critical volume fractions of solid fillers, which creates thermal transport pathways because high conductivity filler particles are in direct physical contact with one another. [8] However, percolated particles generally interface with each other through point-like contacts. This issue serves as a primary bottleneck for overall TIM thermal performance, independent of the filler materials employed. Physical joining methods such as welding or sintering of filler particles can increase the contact area between fillers for improved thermal transport. [9] However, forming these rigid connections requires additional processing steps and does not completely address the issue of composite stiffness for moderate to high filler loadings.Emerging TIMs consisting of room-temperature liquid metals (LMs) seek to improve the composite thermal conductivity by addressing the issues affecting thermal resistance and mechanical compliance. [7,10] Gallium-based LMs and its eutectic alloys (i.e., eGaIn and eGaInSn) have thermal conductivity values between 16-30 W m -1 K -1 depending on their elemental composition. [11] Unlike gallium which melts at 30 °C, both Thermal interface materials based on room temperature liquid metals (LMs) are promising candidates for improving thermal management of flexible electronics, microelectronics packaging, and energy storage devices. However, use of these materials is limited by their corrosivity and reactivity. Here, the fabrication and thermal characterization of multiphase soft composites consisting of LM and non-reactive silicon carbide (SiC) particles that are either uncoated or Ag-coated (Ag-SiC) are demonstrated. The LM-SiC (and LM-Ag-SiC) mixtures show thermal conductivities approaching 50 W m -1 K -1 at 40 vol% particles. Corrosion issues with aluminum-based components are...

Polymer matrix composites containing room temperature liquid metal (LM) microdroplets offer a unique set of thermo-mechanical characteristics that makes them attractive candidates for high performance thermal interface materials. However, to achieve the desired level of the composite thermal conductivity, effective bridging of such fillers into interconnected percolation networks needs to be induced. Thermal percolation of the LM microdroplets requires two physical barriers to be overcome. First, the LM microdroplets must directly contact each other through the polymer matrix. Second, the native oxide shell on the LM microdroplet must also be ruptured. In this work, we demonstrate that both physical barriers can be penetrated to induce ample bridging of the LM microdroplets and thereby achieve higher thermal conductivity composites. We accomplish this through a synergistic combination of solid silver and LM fillers, tuning of the silicone oil “matrix” viscosity, and sample compression. We selected silver as the solid additive because it rapidly alloys with gallium to form microscale needles that could act as additional paths that aid in connecting the LM droplets. We systematically explore the impact of the composition (filler type, volume fraction, and matrix oil viscosity) and applied pressure on the thermal conductivity and multiscale structure of these composites. We reveal the microscopic mechanism underlying the macroscopic experimental trends and also identify an optimal composition of the multiphase Ag–LM–Silicone oil composite for thermal applications. The identified design knobs offer path for developing tunable LM-based polymer composites for microelectronics cooling, biomedical applications, and flexible electronics.