Challenges:
The rapid advancement of electronics, thermal management systems, and flexible devices has heightened the demand for innovative materials that combine mechanical flexibility with efficient thermal conductivity. Liquid metal-elastomer composites have emerged as promising candidates in this field due to their unique ability to provide both softness and high electrical or thermal performance. These composites are integral to the development of flexible electronics, soft robotics, and advanced thermal interface materials, where strong and reliable bonding between the composite and various substrates is essential for device functionality and durability.
However, current approaches to adhering liquid metal-elastomer composites to substrates face significant challenges. Traditional adhesion methods often result in weak bonds that are prone to failure under mechanical stress, limiting the reliability and lifespan of the devices. Additionally, these methods typically lack versatility, making it difficult to achieve strong adhesion across different types of substrates such as metals, glass, and polymers. Furthermore, existing techniques do not allow for precise tuning of the composite’s mechanical and thermal properties, which is crucial for optimizing performance in diverse applications. These limitations hinder the broader adoption and effectiveness of liquid metal-elastomer composites in critical technological advancements
Solution:
A method enhances the adhesion of liquid metal-elastomer composites to various substrates through a two-step surface treatment process. Initially, the substrate surface is activated using oxygen plasma, creating a reactive surface. This is followed by functionalizing the activated surface with aminopropyltriethoxysilane (APTES), which introduces chemical groups that form covalent bonds with the elastomer chains of the composite. The composite consists of eutectic gallium-indium (EGaIn) droplets dispersed within an Ecoflex elastomer matrix. By adjusting the liquid metal droplet size (ranging from 2 to 60 µm) and volume fraction (up to 60%), the mechanical and thermal properties of the composite can be finely tuned. This technique achieves strong adhesion on various substrates, including metals, glass, and polymers, making it suitable for applications in electronics, thermal interface materials, and flexible devices where robust bonding is crucial.
This approach stands out due to its ability to significantly increase fracture energy—up to 7800 J/m²—by creating strong covalent bonds between the composite and the substrate. Unlike untreated samples, which exhibit much lower adhesion, this method ensures cohesive failure within the composite rather than at the interface, enhancing durability and reliability. The versatility in tuning the composite's properties independently of the substrate allows for customized solutions across different applications. Additionally, the process does not require additional mechanical support or encapsulation, simplifying fabrication and expanding its commercial potential. Its effectiveness across multiple substrates and its capacity to maintain superior thermal and mechanical performance under various conditions distinguish this technology in the field of liquid metal composites.
Advantages:
Potential Applications:
Strong bonding of liquid metal composite. a) Schematic representation of liquid metal composite adhesion without (left) and with (right) chemical anchoring. b) Fracture energy (Gc) versus displacement of representative LM composites (ϕ = 20%, d = 2 µm) undergoing peeling. c) Fracture energies of untreated and chemically anchored samples (ϕ = 20%, d = 2 µm). Error bars represent the standard deviation for n = 3. d) Strong LM composite adhesive supporting bricks of total mass 6.8 kg from a 15 mm wide, pre-cracked peel specimen.