Corrosion-Resistant Functional Diamond Coatings for Reliable Interfacing of Liquid Metals with Solid Metals.

Interfacing of surfaces with gallium-based liquid metals – approaches for mitigation and augmentation of liquid metal adhesion on surfaces

Gallium-based liquid metals such as eutectic gallium-indium (EGaIn) offer a unique combinationof high conductivity, high deformability, and biocompatibility, making them promising candidates for applications in soft electronics and shape-programmable drug carriers. However, their performance is governed almost entirely by a rigid and spontaneously forming single-nanometer thick gallium oxide skin. While this shell can provide structural integrity and shape retention, it often leads to unwanted adhesion, suppressed flow, and electrical insulation. The dynamics of both oxide growth chemical kinetics and mechanical rupture complicate efforts to quantify the rheological properties and motivate precise interfacial control strategies. This dissertation addresses this challenge by developing chemical strategies to manipulateEGaIn across length scales - from single nanoparticles to microdroplets to macroscopic films. Through coordinated use of solvents, acids, and thiolated ligands, the oxide thickness, stiffness, and regeneration timescales of the oxide layer are tuned to enable controlled deformation, stabilization, or electromechanical activation on demand. Suppressing oxide regeneration lowers the interfacial modulus, replacing shell-dominated bending with more fluid-like yielding. The resulting thinner oxide enables sharper rupture events and faster conductivity switching, characteristics applicable in pressure sensitive electronics. At the nanoscale, conductive atomic force microscopy confirms that strong acidificationfollowed by thiolation in nonpolar media softens the oxide shell. This treatment lowers rupture thresholds and reduces the force required for electromechanical activation by approximately 40% relative to oxide-rich nanoparticles. A complementary microfluidic platform is established to engineer liquid metal architectures with tunable size, aspect ratio, and deformability by systematically varying solvent acidity and hydrodynamic pressure. In neat ethanol, the oxide is thickest and resists pinch-off, producing bending-dominated ruptures, whereas increasing acidity suppresses oxide regeneration and restores classical surface-tension-driven breakup. However, once the oxide shell fully dissolves, droplets rapidly coalesce back into bulk metal, making stable suspensions unattainable without interfacial reinforcement. To stabilize acidic dispersions, a thiol-PEG click complex is introduced to form a stericinterfacial boundary that prevents coalescence while preserving conductivity. The strain-promoted thiol-azide-alkyne cycloaddition (SPAAC) click complexation remains intact across a wide pH range. As a result, the same click-enabled interface can be applied to elongated drug carriers or spherical conductive droplets, depending on whether biochemical release or electronic connectivity is prioritized. Collectively, these findings establish that gallium oxide interfaces do not behave as inertbarriers but as chemically programmable mechanical skins. Depending on oxidation state and ligand coverage, the interface can transition from an elastic shell that bends, to a plastic layer that buckles, to a fully Newtonian surface that flows. Rather than viewing liquid metals as passive conductors, this work positions them as reconfigurable platforms for shape-adaptive drug carriers, stress-reporting sensors, and flow-activated electronic inks, where performance is engineered at the interface, not in the core.--Author's abstract

Gallium-based liquid metals (GLMs) are promising anode materials for lithium-ion batteries due to their low-melting point, fluidity, high-electrical and -thermal conductivity, and high-theoretical capacity for Li (769 mAh/g, Li2Ga). Notably, GLMs undergo a reversible liquid-to-solid-to-liquid transition during lithiation and delithiation, enabling a self-healing mechanism that mitigates surface defects. This mechanism extends the cycle life of anodes utilizing GLMs either as active materials( 1–6 ) or in combination with high-volume expansion materials such as silicon (~400%)( 7–9 ).Fundamental studies on the self-healing mechanism of GLMs are limited. Previous investigations have primarily relied on macroscopic characterizations such as X-ray diffraction (XRD) in bulk electrodes( 3,10 ) or in situ transmission electron microscopy (TEM) on individual GLM nanoparticles (NPs) in solid-state cells open to the environment( 6,11 ). In this work, we adopt a multi-scale approach to gain insights into the (de)lithiation mechanism. We conducted: (1) in situ TEM observations of GLM NPs on a TEM grid current collector to simultaneously track lithiation/delithiation dynamics across multiple nanoparticles; (2) cryogenic TEM where GLM NPs on a TEM grid are cycled in a lithium-ion battery electrolyte, and the grid is subsequently transferred to a cryo-TEM for high-resolution interfacial characterization of the GLM NPs; and (3) cryogenic focused-ion beam tomography to analyze structural changes in a composite electrode comprised of GLM NPs, Super P carbon, and PVDF binder on a Cu current collector over continuous cycles within a coin or pouch cell. By investigating GLMs at multiple length scales, this study advances the understanding of how the lithiation/delithiation mechanism of GLM NPs influences capacity fade in lithium-ion batteries. In a broader context, this study establishes a framework for future multi-length scale investigations into battery materials.References Jin, X. et al. Transferring Liquid Metal to form a Hybrid Solid Electrolyte via a Wettability-Tuning Technology for Lithium-Metal Anodes. Adv. Mater. 34, 2200181 (2022).Zhu, M., Li, S., Li, B. & Yang, S. A liquid metal-based self-adaptive sulfur–gallium composite for long-cycling lithium–sulfur batteries. Nanoscale 11, 412–417 (2019).Guo, X. et al. A Self-Healing Room-Temperature Liquid-Metal Anode for Alkali-Ion Batteries. Adv. Funct. Mater. 28, 1804649 (2018).Pu, J. et al. Liquid Metal-Based Stable and Stretchable Zn-Ion Battery for Electronic Textiles. Adv. Mater. 36, 2305812 (2024).Liu, G. et al. Soft, Highly Elastic, and Discharge-Current-Controllable Eutectic Gallium–Indium Liquid Metal–Air Battery Operated at Room Temperature. Adv. Energy Mater. 8, 1703652 (2018).Huang, C. et al. Alkali-ion Batteries by Carbon Encapsulation of Liquid Metal Anode. Adv. Mater. n/a, 2309732.Hapuarachchi, S. N. S. et al. Utilizing Room Temperature Liquid Metals for Mechanically Robust Silicon Anodes in Lithium-Ion Batteries. Batter. Supercaps 1, 122–128 (2018).Ju, Z. et al. Assembled MXene–Liquid Metal Cages on Silicon Microparticles as Self-Healing Battery Anodes. Nano Lett. 24, 6610–6616 (2024).Zhao, Z. et al. Liquid Metal Remedies Silicon Microparticulates Toward Highly Stable and Superior Volumetric Lithium Storage. Adv. Energy Mater. 12, 2103565 (2022).Wang, K. et al. Core-shell GaSn@rGO nanoparticles as high-performance cathodes for room-temperature liquid metal batteries. Scr. Mater. 217, 114792 (2022).Liang, W. et al. Nanovoid Formation and Annihilation in Gallium Nanodroplets under Lithiation–Delithiation Cycling. Nano Lett. 13, 5212–5217 (2013).

Gallium-based liquid metals (LMs) featuring both high conductivity and fluidity are ideal conductors for soft and stretchable electronics. However, their liquid nature is a double-edged sword in many key applications since LMs are inherently prone to mechanical damage. Although additional encapsulation is frequently used for the protection of delicate LM electrodes, it hinders the electrical interfacing with other objects for interconnection, sensing, and stimulation. Here, different from conventional patterning methods that deposit LM on or inside substrates, we for the first time report a simple strategy to create surface-embedded LM of eutectic gallium-indium (EGaIn) circuits with mechanical damage endurance. This was achieved by using direct magnetic printing to overcome the high surface tension of LM, allowing it to be passively filled into the laser-patterned microgrooves on soft substrates. We show that the surface-embedded LM circuits are resistant to mechanical erasure, washing, and peeling. We also show the applications of our surface-embedded LM electrodes in respiration monitoring and electrical stimulation of nerves. This work provides a simple and efficient way to create mechanically reliable LM microelectrodes, holding great promise for wearable and implantable bioelectronics.

We report the fabrication and characterization of a reversible resonant frequency tunable antenna based on liquid metal actuation. The antenna is composed of a coplanar waveguide fed monopole stub printed on a copper-clad substrate, and a tunnel-shaped microfluidic channel linked to the printed metal. The gallium-based liquid metal can be injected and withdrawn from the channel in response to an applied air pressure. The gallium-based liquid metal is treated with hydrochloric acid to eliminate the oxide layer, and associated wetting/sticking problems, that arise from exposure to an ambient air environment. Elimination of the oxide layer allows for reliable actuation and repeatable and reversible tuning. By controlling the liquid metal slug on-demand with air pressure, the liquid metal can be readily controllable to connect/disconnect to the monopole antenna so that the physical length of the antenna reversibly tunes. The corresponding reversible resonant frequency changes from 4.9 GHz to 1.1 GHz. The antenna properties based on the liquid metal actuation were characterized by measuring the reflection coefficient and agreed well with simulation results. Additionally, the corresponding time-lapse images of controlling liquid metal in the channel were studied.

Gallium-based liquid metals (GBLMs) have both high fluidity and electrical conductivity and have recently raised great hopes with the promise of realizing soft electronics. By soft electronics, we mean electronic components that can retain their function while being bent and elongated. However, a nanometer-thick oxide skin forms on the GBLM surface, causing atypical interfacial behaviors, and the underlying physics remains unclear. Here, we present the results of a combined experimental and theoretical investigation of the dependence of contact angle of liquid phase eutectic gallium–indium (EGaIn) with oxide skin on van der Waals attraction. Our experiments showed that when EGaIn has an oxide skin, only the static advancing contact angle, not the equilibrium and static receding contact angles, can be specified. We suggest a mathematical model that explains how the static advancing contact angle of EGaIn depends on van der Waals force and the tension exerted on the oxide skin, elucidating the physics that determines the contact angle of EGaIn with the oxide skin in microscopic analysis. Our study helps us to better understand the interface of GBLMs, providing new insight into microfabrication techniques for GBLMs.

Gallium-based room-temperature liquid metals have enormous potential for realizing various applications in electronic devices, heat flow management, and soft actuators. Filling narrow spaces with a liquid metal is of great importance in rapid prototyping and circuit printing. However, it is relatively difficult to stretch or spread liquid metals into desired patterns because of their large surface tension. Here, we propose a method to fabricate a particle-based porous material which can enable the rapid and spontaneous diffusion of liquid metals within the material under a capillary force. Remarkably, such a method can allow liquid metal to diffuse along complex structures and even overcome the effect of gravity despite their large densities. We further demonstrate that the developed method can be utilized for prototyping complex three-dimensional (3D) structures via direct casting and connecting individual parts or by 3D printing. As such, we believe that the presented technique holds great promise for the development of additive manufacturing, rapid prototyping, and soft electronics using liquid metals.

This work discusses the attributes, fabrication methods, and applications of gallium‐based liquid metal particles. Gallium‐based liquid metals combine metallic and fluidic properties at room temperature. Unlike mercury, which is toxic and has a finite vapor pressure, gallium possesses low toxicity and effectively zero vapor pressure at room temperature, which makes it amenable to many applications. A variety of fabrication methods produce liquid metal particles with variable sizes, ranging from nm to mm (which is the upper limit set by the capillary length). The liquid nature of gallium enables fabrication methods—such as microfluidics and sonication—that are not possible with solid materials. Gallium‐based liquid metal particles possess several notable attributes, including a metal–metal oxide (liquid–solid) core–shell structure as well as the ability to self‐heal, merge, and change shape. They also have unusual phase behavior that depends on the size of the particles. The particles have no known commercial applications, but they show promise for drug delivery, soft electronics, microfluidics, catalysis, batteries, energy harvesting, and composites. Existing challenges and future opportunities are discussed herein.

Gallium-based liquid metals (LMs) are widely used for stretchable and reconfigurable electronics thanks to their fluidic nature and excellent conductivity. These LMs possess attractive optical properties for photonics applications as well. However, due to the high surface tension of the LMs, it is challenging to form LM nanostructures with arbitrary shapes using conventional nanofabrication techniques. As a result, LM-based nanophotonics has not been extensively explored. Here, a simple yet effective technique is demonstrated to deterministically fabricate LM nanopatterns with high yield over a large area. This technique demonstrates for the first time the capability to fabricate LM nanophotonic structures of various precisely defined shapes and sizes using two different LMs, that is, liquid gallium and liquid eutectic gallium-indium alloy. High-density arrays of LM nanopatterns with critical feature sizes down to ≈100nm and inter-pattern spacings down to ≈100nm are achieved, corresponding to the highest resolution of any LM fabrication technique developed to date. Additionally, the LM nanopatterns demonstrate excellent long-term stability under ambient conditions. This work paves the way toward further development of a wide range of LM nanophotonics technologies and applications.

We investigated frequency tunability of a microfluidic-based antenna using on-demand manipulation of a gallium-based liquid metal alloy. The fluidic antenna was fabricated by polydimethylsiloxane (PDMS) and filled with the gallium-based liquid metal alloy (Galinstan ® ). It is composed of a digital number “7”-shaped feedline, and a square-shaped and a digital number “6”-shaped patterns, which are all implemented with the liquid metal. The gallium-based liquid metal was adhered to the channel surface due to its viscous oxide layer originating from the gallium oxide forming when it exposed to the air environment. We treated the liquid metal with hydrochloric acid solution to remove the oxide layer on the surface resulting in easy movement of the liquid metal in the channel, as the liquid metal surface has been transformed to be non-wettable. We controlled the physical length of the liquid metal slug filled in feedline with an applied air pressure, resulting in tuning the resonant frequency ranging from 2.2 GHz to 9.3 GHz. The fluidic antenna properties using the liquid metal’s electrical conductivity and mobility were characterized by measuring the return loss (S11), and also simulated with CST Microwave Studio.

Surface Chemistry of Gallium-Based Liquid Metals

Gallium-based liquid metal (LM) is regarded as one of the most promising candidates for the new-generation jigsaw of stretchable electronics. Nonetheless, the obstacle for the LM application lies in its high surface tension and easy fluidity which leads to great difficulty in handling and processing. Herein, a cross-mechanochemistry between liquid metal and inorganic solid, mediated via the coordination binding between the empty electronic orbits of the former and the lone electron pair of the latter is reported. The mechanism is validated via density functional theory calculation and electron energy loss spectroscopy, and experimentally proven to be universally applicable for various liquid metals and inorganic solids. With the unique mechanochemistry, simple ball milling allows on-demand transformation of the liquid metal into a low-surface-tension liquid, semi-solid paste, or even solid powder. The overcoming of the intrinsic high surface tension of the liquid metal with this approach unleashes the freedom to easily process the liquid metal composites into polymer composites or as direct molding processable paste and printable electronic ink.

We demonstrate a magnetocaloric ferrofluid based on a gadolinium saturated liquid metal matrix, using a gallium-based liquid metal alloy as the solvent and suspension medium. The material is liquid at room temperature, while exhibiting spontaneous magnetization and a large magnetocaloric effect. The magnetic properties were attributed to the formation of gadolinium nanoparticles suspended within the liquid gallium alloy, which acts as a reaction solvent during the nanoparticle synthesis. High nanoparticle weight fractions exceeding 2% could be suspended within the liquid metal matrix. The liquid metal ferrofluid shows promise for magnetocaloric cooling due to its high thermal conductivity and its liquid nature. Magnetic and thermoanalytic characterizations reveal that the developed material remains liquid within the temperature window required for domestic refrigeration purposes, which enables future fluidic magnetocaloric devices. Additionally, the observed formation of nanometer-sized metallic particles within the supersaturated liquid metal solution has general implications for chemical synthesis and provides a new synthetic pathway toward metallic nanoparticles based on highly reactive rare earth metals.

Gallium-based liquid metals (LMs) are materials that possess some unique properties. Just like any other metal, they have high thermal conductivity and low interfacial resistance, but they are in a liquid phase at room temperature. In contrast to mercury alloys, gallium alloys are non-toxic. They don’t evaporate and they can’t be inhaled. The viscosity of those alloys is very similar to water, but they are six times as dense as water. All those properties make Gallium-based liquid metals very good candidates for thermal interface material (TIM) in electronics applications. On the other hand, the reaction and incompatibility of those alloys with some metals is one of the challenges for this type of TIM. The other challenge is that those materials are not just thermally, but also electrically conductive and that is not a desirable property for TIM. A suitable barrier that will prevent any leakage of LMs and the best way to apply the appropriate volume of LM in high-volume production (HVP) would be one of the most important things for any application. A key challenge is applying the liquid metal consistently through a traditional dispensing method due to its property and behavior which involves high surface tension. Through advanced dispensing techniques like jetting technology liquid metal can be applied reliably on a flat, uneven surface or in arrays of minuscule confined spaces or cavities. This paper highlights the dispensing quality, weight repeatability from one substrate to another, and valve hardware stability. This paper will also address the challenges faced during dispensing of liquid metal in high volume manufacturing, and how to achieve desired bondline thickness with jet dispensing for higher throughput and process reliability.

Due to their sequence-directed functions and excellent biocompatibility, smart DNA microgels have attracted considerable research interest, and the combination of DNA microgels with functional nanostructures can further expand their applications in biosensing and biomedicine. Gallium-based liquid metals (LMs) exhibiting both fluidic and metallic properties hold great promise for the development of smart soft materials; in particular, LM particles upon sonication can mediate radical-initiated polymerization reactions, thus allowing the combination of LMs and polymeric matrix to construct "soft-soft" materials. Herein, by forming active surfaces under sonication, LM nanoparticles (LM NPs) initiated localized radical polymerization reactions allow the combination of functional DNA units and different polymeric backbones to yield multifunctional core/shell microgels. The localized polymerization reaction allows fine control of the microgel compositions, and smart DNA microgels with tunable catalytic activities can be constructed. Moreover, due to the excellent photothermal effect of LM NPs, the resulting temperature gradient between microgels and surrounding solution upon NIR light irradiation can drive the oriented locomotion of the microgels, and remote control of the activity of these smart microgels can be achieved. These microgels may hold promise for various applications, such as the development of in vivo and in vitro biosensing and drug delivery systems.