A crack compensation strategy for highly stretchable conductors based on liquid metal inclusions

Liquid Metal-Based Self-Healing Conductors for Flexible and Stretchable Electronics

Flexible and stretchable electronics rely on compliant conductors as essential building materials. However, these materials are susceptible to wear and tear, leading to degradation over time. In response to this concern, self-healing conductors have been developed to prolong the lifespan of functional devices. These conductors can autonomously restore their properties following damage. Conventional self-healing conductors typically comprise solid conductive fillers and healing agents dispersed within polymer matrices. However, the solid additives increase the stiffness and reduce the stretchability of the resulting composites. There is growing interest in utilizing gallium-based liquid metal alloys due to their exceptional electrical conductivity and liquid-phase deformability. These liquid metals are considered attractive candidates for developing compliant conductors capable of automatic recovery. This perspective delves into the rapidly advancing field of liquid metal-based self-healing conductors, exploring their design, fabrication, and critical applications. Furthermore, this article also addresses the current challenges and future directions in this active area of research.

Ultrastretchable Electrically Self-Healing Conductors Based on Silver Nanowire/Liquid Metal Microcapsule Nanocomposites

Stretchable conductive nanocomposites are essential for deformable electronic devices. These conductors currently face significant limitations, such as insufficient deformability, significant resistance changes upon stretching, and drifted properties during cyclic deformations. To tackle these challenges, we present an electrically self-healing and ultrastretchable conductor in the form of bilayer silver nanowire/liquid metal microcapsule nanocomposites. These nanocomposites utilize silver nanowires to establish their initial excellent conductivity. When the silver nanowire networks crack during stretching, the microcapsules are ruptured to release the encased liquid metal for recovering the electrical properties. This self-healing capability allows the nanocomposite to achieve ultrahigh stretchability for both uniaxial and biaxial strains, minor changes in resistance during stretching, and stable resistance after repetitive deformations. The conductors have been used to create skin-attachable electronic patches and stretchable light-emitting diode arrays with enhanced robustness. These developments provide a bioinspired strategy to enhance the performance and durability of conductive nanocomposites.

Breakup-Free and Colorful Liquid Metal Thin Films via Electrochemical Oxidation

Thin-film metal conductors featuring high conductivity and stretchability are basic building blocks for high-performance conformable electronics. Gallium-based liquid metals are attractive candidates for thin-film conductors due to their intrinsic stretchability and ease of processing. Moreover, the phase change nature of liquid metal provides an opportunity to create conformal electronics in a substrate-free manner. However, thin liquid metal films tend to break during the solid-to-liquid transition due to the high surface tension of liquid metal. Here, we created breakup-free liquid metal thin films by the electrochemical oxidation of solid gallium films. We show that electrochemical oxidation can enhance the mechanical strength of the gallium oxide layer and its interfacial adhesion to the gallium core. When heated to the liquid state, the oxidized gallium films can maintain their structural integrity on various solid substrates, hydrogels, and even the water surface. The solid-liquid phase change-induced stiffness decrease allowed the gallium films to be conformably attached to various nonplanar surfaces upon heating or water transfer printing. Moreover, we also found that enhanced electrochemical oxidation can result in the formation of structure color due to nanoporous structures on the film surface. We also demonstrate the applications of oxidized liquid metal films in functional electronics, electrophysiological monitoring, and tattoo art.

Formation of inorganic liquid gallium particle-manganese oxide composites

Gallium (Ga) is a low melting point post-transition metal that, under mild mechanical agitation, can form micron and submicron-sized particles with combined fluid-like and metallic properties. In this work, an inorganic network of Ga liquid metal particles was synthesised via spontaneous formation of manganese (Mn) oxide species on their liquid metallic surfaces forming an all-inorganic composite. The micron-sized Ga particles formed by sonication were connected together by Mn oxide nanostructures spontaneously established from the reduction of a Mn salt in aqueous solution slightly above the melting point of Ga. The formed Mn oxide nanostructures were found to coalesce from the surface of the Ga particles into a continuous inorganic network. The morphology of the composites could be altered by varying the Mn salt concentration and by performing post-treatment annealing. The composites presented a shell of various Mn oxide nanostructures including wrinkled sheets, rods and nanoneedles, around spherical liquid Ga particles, and a liquid metal core. The photoelectric and optical properties of the composites were thoroughly characterised, which revealed decreasing bandgaps and valence band edge characteristics as a function of increased Mn oxide coverage. The photoluminescence properties of the composites could be also engineered by increasing the Mn oxide coverage. The all-inorganic liquid Ga composite could be formed via a straightforward reduction reaction of a Mn-rich salt at the surface of liquid Ga particles with tunable surface properties for future optoelectronic applications.