Stretchable high‐dielectric‐constant materials are crucial for electronic applications in emerging domains such as wearable computing and soft robotics. While previous efforts have shown promising ...materials architectures in the form of dielectric nano‐/microinclusions embedded in stretchable matrices, the limited mechanical compliance of these materials significantly limits their practical application as soft energy‐harvesting/storage transducers and actuators. Here, a class of liquid metal (LM)–elastomer nanocomposites is presented with elastic and dielectric properties that make them uniquely suited for applications in soft‐matter engineering. In particular, the role of droplet size is examined and it is found that embedding an elastomer with a polydisperse distribution of nanoscale LM inclusions can enhance its electrical permittivity without significantly degrading its elastic compliance, stretchability, or dielectric breakdown strength. In contrast, elastomers embedded with microscale droplets exhibit similar improvements in permittivity but a dramatic reduction in breakdown strength. The unique enabling properties and practicality of LM–elastomer nanocomposites for use in soft machines and electronics is demonstrated through enhancements in performance of a dielectric elastomer actuator and energy‐harvesting transducer.
A liquid‐metal (LM)–elastomer nanocomposite is presented as a stretchable dielectric material. This material's architecture shows a unique combination of enhanced electric permittivity, controlled dielectric breakdown strength, and rubber‐like mechanical properties. These properties enable LM–elastomer nanocomposites to have potentially transformative impact on soft materials actuation, energy storage, and energy harvesting.
Elastomers embedded with droplets of liquid metal (LM) alloy represent an emerging class of soft multifunctional composites that have potentially transformative impact in wearable electronics, ...biocompatible machines, and soft robotics. However, for these applications it is crucial for LM alloys to remain liquid during the entire service temperature range in order to maintain high mechanical compliance throughout the duration of operation. Here, LM‐based functional composites that do not freeze and remain soft and stretchable at extremely low temperatures are introduced. It is shown that the confinement of LM droplets to micro‐/nanometer length scales significantly suppresses their freezing temperature (down to −84.1 from −5.9 °C) and melting point (down to −25.6 from +17.8 °C) independent of the choice of matrix material and processing conditions. Such a supercooling effect allows the LM inclusions to preserve their fluidic nature at low temperatures and stretch with the surrounding polymer matrix without introducing significant mechanical resistance. These results indicate that LM composites with highly stabilized droplets can operate over a wide temperature range and open up new possibilities for these emerging materials, which are demonstrated with self‐powered wearable thermoelectric devices for bio‐sensing and personal health monitoring at low temperatures.
Liquid metal droplets are tailored to remain liquid at temperatures as low as −85 °C. Their polymer composites are soft and stretchable even at extreme cold conditions and show exceptional thermal and electrical performance. This unique combination of properties is enabling for emerging technologies, including self‐powered electronics, deep‐sea underwater robots, and space applications.
Liquid metal elastomer composites have gained significant attention in advanced technologies including wearable electronics, soft robotics, and human-computer interactions. This is due to the ...combination of metallic conductivity and fluidic properties of liquid metal (LM) inclusions in addition to their facile fabrication process. With the emergence of gallium-based liquid metal nanocomposites and advances in synthesis and integration of LM nanoparticles in a variety of polymer matrices, there is a pressing need for a materials design tool to accelerate the development of these multifunctional composites. Here, we introduce a double inclusion (DI) model capable of predicting the properties of polymer composites with core-shell liquid metal droplets. The size-dependent elasticity of LM inclusions is modeled by considering the solid gallium oxide interphase between the liquid metal core and the solid polymer matrix. As the size of inclusions reduces from tens of microns to tens of nanometers, the role of the oxide interface (shell) becomes more dominant. The results of the DI model show excellent agreement with finite element analysis and experimental results for a wide range of droplet sizes and volume fractions. This model provides a design framework for the synthesis of LM composites with tailored multifunctional properties.
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While aramid fibers have been innovative for ballistic protection because of their high energy absorption, minimal usage has been applied to continuous fiber reinforced polymer (CFRP) composites in ...structural applications. One of the challenges with aramid fibers results from their processing, which yields smooth and chemically inert surfaces that limit the ability of the fibers to adhere to polymeric matrices. Here, it is shown that aramid nanofibers can adhere to the surface of macroscale aramid reinforcements to improve the strength of the composite interface and reinforce the matrix as well. Aramid nanofibers are formed through the dissolution of aramid fibers followed by isolation and dispersion into an epoxy matrix. When employed in CFRP, aramid nanofibers prove to be effective reinforcement agents through improvement in both matrix properties as well as modifying the interfacial shear strength, which leads to improved interlaminar shear strength and fracture toughness. The interface enhancements are attributed to hydrogen bonding and π-π coordination between the aramid nanofibers and the macro fibers providing improved transfer load from the fiber to the matrix. This work demonstrates that aramid nanofibers may provide the robust mechanical properties that are necessary for structural applications while utilizing a cost-effective and convenient nanoscale building block.
Coating inkjet‐printed traces of silver nanoparticle (AgNP) ink with a thin layer of eutectic gallium indium (EGaIn) increases the electrical conductivity by six‐orders of magnitude and significantly ...improves tolerance to tensile strain. This enhancement is achieved through a room‐temperature “sintering” process in which the liquid‐phase EGaIn alloy binds the AgNP particles (≈100 nm diameter) to form a continuous conductive trace. Ultrathin and hydrographically transferrable electronics are produced by printing traces with a composition of AgNP‐Ga‐In on a 5 µm‐thick temporary tattoo paper. The printed circuit is flexible enough to remain functional when deformed and can support strains above 80% with modest electromechanical coupling (gauge factor ≈1). These mechanically robust thin‐film circuits are well suited for transfer to highly curved and nondevelopable 3D surfaces as well as skin and other soft deformable substrates. In contrast to other stretchable tattoo‐like electronics, the low‐cost processing steps introduced here eliminate the need for cleanroom fabrication and instead requires only a commercial desktop printer. Most significantly, it enables functionalities like “electronic tattoos” and 3D hydrographic transfer that have not been previously reported with EGaIn or EGaIn‐based biphasic electronics.
Stretchable thin‐film electronics that can be transferred to 3D surfaces or human skin are created by a versatile, fast, and cost‐effective processing method. The circuits are composed of inkjet‐printed traces of silver nanoparticles (AgNPs) that are coated with a eutectic gallium indium (EGaIn) liquid alloy. The EGaIn coating dramatically reduces the resistivity of the AgNP traces and enables stretchable functionality.
Liquid metal polymer composites are an emerging class of functional materials with potentially transformative impacts in wearable electronics, soft robotics, and human‐computer interactions. By ...employing different processing methods, room temperature liquid metal inclusions can be embedded in insulating polymers like elastomers to incorporate functional properties of metals while the matrix remains soft and stretchable. These solid–liquid composites offer an interesting, yet complex multifunctional material system. In this review, we present an exclusive overview of the synthesis methods, structural and functional properties, and applications of gallium‐based liquid metal polymer composites. Common methods to control the size of liquid metal inclusions and their interaction in polymers are discussed. Moreover, the effect of liquid metal microstructures on the overall properties of the composites is summarized. We also highlight the new trends in terms of material composition, printing process, and novel applications of liquid metal polymer composites in intelligent systems.
Continuous powering of wearable electronics and personalized biomonitoring systems remains a great challenge. One promising solution is the use of thermoelectric generators (TEGs) that convert body ...heat to electricity. These energy harvesters must conform to curved surfaces and minimize thermal barriers to maintain efficiency while still exhibiting durability under large deformations. Here, highly efficient, stretchable thermoelectric generators made of inorganic semiconductors and printed multifunctional soft matter are introduced. Liquid metal elastomer composites with tailored microstructures are printed as highly conductive thermal interface materials and stretchable interconnects. Additionally, elastomer composites with hollow microspheres are formulated to print a deformable and lightweight thermal insulator within the device. These stretchable thermoelectric wearables show an excellent performance by generating an open‐circuit voltage of 392 mV and a power density of ≈650 µW cm−2 at ∆T = 60 °C and withstanding more than 15 000 stretching cycles at 30% strain. Furthermore, the additive manufacturing process is leveraged by direct writing of the TEGs on textiles to demonstrate their seamless integration and by 3D printing of stretchable heatsinks to maintain a large temperature gradient across the device and to study the effect of convective heat transfer on device performance.
Eutectic gallium‐indium particles and hollow thermoplastic microspheres are mixed into elastomers to create functional inks for printing stretchable thermoelectric devices. This fabrication method results in durable thermoelectric generators with high power density while enabling device customization, 3D printing of stretchable heatsinks, and seamless integration of thermoelectrics into textiles for wearable applications.
Liquid metal nanocomposites Malakooti, Mohammad H; Bockstaller, Michael R; Matyjaszewski, Krzysztof ...
Nanoscale advances,
07/2020, Letnik:
2, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Liquid metal (LM) has attracted tremendous interest over the past decade for its enabling combination of high electrical and thermal conductivity and low mechanical compliance and viscosity. Efforts ...to harness LM in electronics, robotics, and biomedical applications have largely involved methods to encapsulate the liquid so that it can support functionality without leaking or smearing. In recent years, there has been increasing interest in LM "nanocomposites" in which either liquid metal is mixed with metallic nanoparticles or nanoscale droplets of liquid metal are suspended within a soft polymer matrix. Both of these material systems represent an important step towards utilizing liquid metal for breakthrough applications. In this minireview, we present a brief overview of recent progress over the past few years in methods to synthesize LM nanomaterials and utilize them as transducers for sensing, actuation, and energy harvesting. In particular, we focus on techniques for stable synthesis of LM nanodroplets, suspension of nanodroplets within various matrix materials, and methods for incorporating metallic nanoparticles within an LM matrix.
This is a progress report on liquid metal (LM) nanocomposites with focus on synthesis of LM nanodroplets, suspension of nanodroplets within various matrix materials, and methods for incorporating metallic nanoparticles within an LM matrix.
Carbon fiber reinforced polymer (CFRP) composites were fabricated using a novel intrinsically healable isocyanurate-oxazolidone (ISOX) thermosetting matrix. After multiple delamination events, ...repeatable strength recovery of the composites has been demonstrated with a first healing efficiency up to 85% after thermal treatment. The healing mechanism results from transformation of the isocyanurate with epoxide groups to yield new oxazolidone rings at the fracture surface. This novel ISOX polymer utilizes commercial diglycidyl ether of bisphenol F (DGEBF) and toluene diisocyanate to produce a high cross-link density thermoset with a glass transition temperature (Tg) up to 285 °C, and 99.5% of the composite weight remains at 300 °C. The strength and stiffness of the composites are comparable with an engineering grade polymer matrix composite typically used in aerospace applications and the thermal stability places the materials in the polybismaleimide performance region although with greater toughness. This polymer exhibits the highest Tg of any self-healing material reported and is composed of low cost reactants, which gives the polymer great potential to function as a major component of an advanced structural composite for extreme environments.
Room temperature liquid metals are an emerging class of functional materials with applications in a variety of soft intelligent systems. In recent years, efforts have been made to integrate liquid ...metal alloys such as eutectic gallium-indium (EGaIn) and eutectic gallium-indium-tin (Galinstan) into wearable electronics, soft robotics, and biomedical devices. One main methodology is reducing the size of the liquid metal (LM) droplets to the micro and nanoscale level. In this review, we present an overview of the recent progress in synthesizing liquid nanoparticles with a focus on the role of processing parameters on their structure and surface properties. Next, the liquid metal nanoparticles are discussed as the functional units in polymer nanocomposites with enhanced electrical and thermal properties. Ultimately, the applications of LM nanoparticles and nanocomposites are presented, followed by a brief outlook on the challenges and future developments of advanced liquid metal material systems.
Sonication and mechanical shearing are scalable processes for creating liquid metal nanoparticles. Optimizing the involved processing parameters is crucial for achieving the desirable structure, surface properties and applications of these nanoparticles.
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