Thermal Interface Materials with High Thermal Conductivity and Low Young’s Modulus Using a Solid–Liquid Metal Codoping Strategy

Abstract

Thermal interface materials (TIMs), as typical thermal functional materials, are highly required to possess both high thermal conductivity and low Young's modulus. However, the naturally synchronized change in the thermal and mechanical properties seriously hinders the development of high-performance TIMs. To tackle such a dilemma, a strategy of codoping solid fillers and liquid metal fillers into polymer substrates is proposed in this study. This strategy includes a large amount of liquid metals that play the role of thermal paths and a small amount of uniformly dispersed solid fillers that further enhance heat conduction. Through the synergistic effect of the liquid metal and solid fillers, the thermal conductivity can be improved, and Young's modulus can be kept small simultaneously. A typical TIM with a volume of 55% gallium-based liquid metal and 15% copper particles as fillers has a thermal conductivity of 3.94 W/(m•K) and a Young's modulus of 699 kPa, which had the maximum thermomechanical performance coefficient compared with liquid metal TIMs and solid filler-doped TIMs. In addition, the thermal conductivity of the solid−liquid metal codoped TIM increased sharply with an increase of liquid metal content, and Young's modulus increased rapidly with an increase of the volume ratio of copper and polymer. The high−low-temperature cycling test and large-size light-emitting diode (LED) application demonstrated that this TIM had stable physical performance. The synergistic effect of the solid fillers and liquid metal fillers provides a broad space to solve the classic tradeoff issue of the mechanical and thermal properties of composites.

Study of the Mechanism of Liquid‐Metal‐Assisted Thermal Interface Materials

“…During the process of mixing the LM with silicone oil, the element gallium on its surface is oxidized by oxygen, forming gallium oxide. The oxide on the surface of each LM particle and a layer of silicone oil adsorbed on the oxides due to hydrogen bonding [19,34,35] reduces the surface tension of the LM particles (the scientific name of the silicone oil used in the experiment is poly(dimethylsiloxane), hydroxy-terminated). Its molecular formula is HO-(C2H6OSi)n-H).…”

“…[ 6–10 ] More recently, LMs or LMs together with other solid high thermal conductivity powders were often added in the thermal pad, gel, and grease as fillers. [ 11–20 ] These studies have obtained good thermal conductivity and thermal resistance. Uppal et al added gallium and silver particle to silicone oil to prepare an Ag–LM–silicone oil composite.…”

“…The maximum thermal conductivity and minimum thermal resistance of their samples are 3.21 Wm −1 K −1 and 2.53 K cm 2 W −1 , respectively. [ 19 ] The thermal conductivity of LM is much lower than ceramic thermal fillers such as AlN (>200 Wm −1 K −1 ) and BN (>200 Wm −1 K −1 ). However, the incorporation of LM can make a much more significant impact than the thermal conductivity itself.…”

Patterned liquid metal embedded in brush-shaped polymers for dynamic thermal management

“…6,23,35,36 In the majority of the research studies, the distribution of LMs within a polymer matrix is achieved through the mechanical mixing of LMs and uncured polymers. For instance, Zhang et al 37 utilized 55% gallium-based LMs and 15% copper particles as fillers to make a composite with uncured Ecoflex, resulting in TIMs with a k value of 3.94 W m À1 K À1 and Young's modulus of 699 kPa. Nonetheless, the large interface thermal resistance between randomly dispersed LMs and the matrix, coupled with inefficient construction of thermal conduction pathways, greatly hindered the efficiency of heat transfer.…”

Exploring Lipoic Acid-Mediated Dynamic Bottlebrush Elastomers as a New Platform for the Design of High-Performance Thermally Conductive Materials

“…Typically, a large dose of the filler is an essential condition to achieve the critical thresholds for the construction of a thermal conductive network, which brings inevitable limitations. Often, the processing procedures (e.g., degassing) dealing with large viscosity precursors are complicated and energy-consuming; the large rigidity of the composites will be difficult to comply with the substrate, leading to an increase in interfacial thermal resistance and high packing force; the cost and density of the composite with large dose of metal fillers are high; etc.…”