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Multiple internal reflection-based absorption-dominant stretchable electromagnetic shielding thin film by incorporating liquid metal grid structure is developed. The device demonstrates high electromagnetic shielding effectiveness (SE) (SET of up to 75 dB) with low reflectance (SER of 1.5 dB at the resonant frequency). The shielding properties of the device can be tuned by adjusting the liquid metal patterned grid spaces upon strain.

Multiple internal reflection-based absorption-dominant stretchable electromagnetic shielding thin film by incorporating liquid metal grid structure is developed. The device demonstrates high electromagnetic shielding effectiveness (SE) (SET of up to 75 dB) with low reflectance (SER of 1.5 dB at the resonant frequency). The shielding properties of the device can be tuned by adjusting the liquid metal patterned grid spaces upon strain. The demand of high-performance thin-film-shaped deformable electromagnetic interference (EMI) shielding devices is increasing for the next generation of wearable and miniaturized soft electronics. Although highly reflective conductive materials can effectively shield EMI, they prevent deformation of the devices owing to rigidity and generate secondary electromagnetic pollution simultaneously. Herein, soft and stretchable EMI shielding thin film devices with absorption-dominant EMI shielding behavior is presented. The devices consist of liquid metal (LM) layer and LM grid-patterned layer separated by a thin elastomeric film, fabricated by leveraging superior adhesion of aerosol-deposited LM on elastomer. The devices demonstrate high electromagnetic shielding effectiveness (SE) (SET of up to 75 dB) with low reflectance (SER of 1.5 dB at the resonant frequency) owing to EMI absorption induced by multiple internal reflection generated in the LM grid architectures. Remarkably, the excellent stretchability of the LM-based devices facilitates tunable EMI shielding abilities through grid space adjustment upon strain (resonant frequency shift from 81.3 to 71.3 GHz @ 33% strain) and is also capable of retaining shielding effectiveness even after multiple strain cycles. This newly explored device presents an advanced paradigm for powerful EMI shielding performance for next-generation smart electronics. [ABSTRACT FROM AUTHOR]

Herein, ultrasoft and ultrastretchable wearable strain sensors enabled by liquid metal fillers in an elastic polymer are described. The wearable strain sensors that can change the effective resistance upon strains are prepared by mixing silicone elastomer with liquid metal (EGaIn, Eutectic gallium-indium alloy) fillers. While the silicone is mixed with the liquid metal by shear mixing, the liquid metal is rendered into small droplets stabilized by an oxide, resulting in a non-conductive liquid metal elastomer. To attain electrical conductivity, localized mechanical pressure is applied using a stylus onto the thermally cured elastomer, resulting in the formation of a handwritten conductive trace by rupturing the oxide layer of the liquid metal droplets and subsequent percolation. Although this approach has been introduced previously, the liquid metal dispersed elastomers developed here are compelling because of their ultra-stretchable (elongation at break of 4000%) and ultrasoft (Young's modulus of <0.1 MPa) mechanical properties. The handwritten conductive trace in the elastomers can maintain metallic conductivity when strained; however, remarkably, we observed that the electrical conductivity is anisotropic upon parallel and perpendicular strains to the conductive trace. This anisotropic conductivity of the liquid metal elastomer film can manipulate the locomotion of a robot by routing the power signals between the battery and the driving motor of a robot upon parallel and perpendicular strains to the hand-written circuit. In addition, the liquid metal dispersed elastomers have a high degree of deformation and adhesion; thus, they are suitable for use as a wearable sensor for monitoring various body motions. [ABSTRACT FROM AUTHOR]

Stretchable and soft piezoresistive composites are appealing for application to tactile sensors, artificial skin, and wearable electronics. The ability of the composites to deform the geometries when they are strained can allow the electrical behavior of the composites to be manipulated. Although rigid metal and semiconductor inclusions have been utilized to create piezoresistive composites, they limit the degree of mechanical deformation. Here, liquid metal (gallium, melting point ≈ 29.7 °C) inclusion into elastomeric foam substrate with 3D open cell morphologies is utilized. Gallium is a fluidic conductor, thus it is possible to infiltrate the liquid metal into the 3D interconnected pore, resulting in soft, stretchable, and shape reconfigurable conductive composites that can change shape and function in response to external stimuli. Applying strain can enable deformation of the liquid metal, generating changes of electrical resistance. Interestingly, it is found that this piezoresistivity of the composite can be positively and negatively manipulated by adjusting the geometries of the liquid metal in the foam. Furthermore, the liquid metal in the elastomeric foam can be reversibly actuated by applying compressive force, resulting in manipulation of the restorative electrical activity of the composites. [ABSTRACT FROM AUTHOR]

Herein, ultrasoft and ultrastretchable wearable strain sensors enabled by liquid metal fillers in an elastic polymer are described. The wearable strain sensors that can change the effective resistance upon strains are prepared by mixing silicone elastomer with liquid metal (EGaIn, Eutectic gallium-indium alloy) fillers. While the silicone is mixed with the liquid metal by shear mixing, the liquid metal is rendered into small droplets stabilized by an oxide, resulting in a non-conductive liquid metal elastomer. To attain electrical conductivity, localized mechanical pressure is applied using a stylus onto the thermally cured elastomer, resulting in the formation of a handwritten conductive trace by rupturing the oxide layer of the liquid metal droplets and subsequent percolation. Although this approach has been introduced previously, the liquid metal dispersed elastomers developed here are compelling because of their ultra-stretchable (elongation at break of 4000%) and ultrasoft (Young’s modulus of

Herein, ultrasoft and ultrastretchable wearable strain sensors enabled by liquid metal fillers in an elastic polymer are described. The wearable strain sensors that can change the effective resistance upon strains are prepared by mixing silicone elastomer with liquid metal (EGaIn, Eutectic gallium-indium alloy) fillers. While the silicone is mixed with the liquid metal by shear mixing, the liquid metal is rendered into small droplets stabilized by an oxide, resulting in a non-conductive liquid metal elastomer. To attain electrical conductivity, localized mechanical pressure is applied using a stylus onto the thermally cured elastomer, resulting in the formation of a handwritten conductive trace by rupturing the oxide layer of the liquid metal droplets and subsequent percolation. Although this approach has been introduced previously, the liquid metal dispersed elastomers developed here are compelling because of their ultra-stretchable (elongation at break of 4000%) and ultrasoft (Young’s modulus of <0.1 MPa) mechanical properties. The handwritten conductive trace in the elastomers can maintain metallic conductivity when strained; however, remarkably, we observed that the electrical conductivity is anisotropic upon parallel and perpendicular strains to the conductive trace. This anisotropic conductivity of the liquid metal elastomer film can manipulate the locomotion of a robot by routing the power signals between the battery and the driving motor of a robot upon parallel and perpendicular strains to the hand-written circuit. In addition, the liquid metal dispersed elastomers have a high degree of deformation and adhesion; thus, they are suitable for use as a wearable sensor for monitoring various body motions.

Liquid metal is a promising conductor material for producing soft and stretchable circuit "boards" that can enable next-generation electronics by electrically connecting and mechanically supporting electronic components. While liquid metal in general can be used to fabricate soft and stretchable circuits, magnetic liquid metal is appealing because it can be used for self-healing electronics and actuators by external magnetic fields. Liquid metal can be rendered into particles that can then be used for sensors and catalysts through sonication. We used this feature to produce "novel" conductive and magnetic particles. Mixing ferromagnetic iron particles into the liquid metal (gallium) produces conductive ferrofluids that can be rendered into gallium-coated iron particles by sonication. The gallium shell of the particles is extremely soft, while the rigid iron core can induce high friction in response to mechanical pressure; thus, hand-sintering of the particles can be used to directly write the conductive traces when the particles are cast as a film on elastic substrates. The surface topography of the particles can be manipulated by forming GaOOH crystals through sonication in DI water, thus resulting in nonwettable circuit boards. These gallium-coated iron particles dispersed in uncured elastomer can be assembled to form conductive microwires with the application of magnetic fields.

Skin-inspired soft and stretchable electronic devices based on functional nanomaterials have broad applications such as health monitoring, human-machine interface, and the Internet of things. Solution-processed conductive nanocomposites have shown great promise as a building block of soft and stretchable electronic devices. However, realizing conductive nanocomposites with high conductivity, electromechanical stability, and low modulus over a large area at sub-100 μm resolution remains challenging. Here, we report a moldable, transferrable, high-performance conductive nanocomposite comprised of an interpenetrating network of silver nanowires and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate). The stacked structure of the nanocomposite synergistically integrates the complementary electrical and mechanical properties of the individual components. We patterned the nanocomposite via a simple, low-cost micromolding process and then transferred the patterned large-area electrodes onto various substrates to realize soft, skin-interfaced electrophysiological sensors. Electrophysiological signals measured using the nanocomposite electrodes exhibit a higher signal-to-noise ratio than standard gel electrodes. The nanocomposite design and fabrication approach presented here can be broadly employed for soft and stretchable electronic devices., Competing Interests: Competing interests L.T. and M.N. are inventors on an International Patent Application (No.: PCT/US22/18015) related to this work filed by the Texas A&M University System. The authors declare that they have no other competing interests.

In this work, a facile and cost-effective approach to assemble metallic wires into two-dimensional (2D) and three-dimensional (3D) freestanding geometries by room-temperature welding is demonstrated. The low melting point of gallium (29.8 °C) enables the welding at room temperature without the aid of high-energy sources required for high-melting-point metals and alloys. The welding enables assembly of solid gallium wires into 2D and 3D geometries that could create freestanding architectures with multiple junctions along any inclined direction. These 2D and 3D freestanding metallic structures are freeze-cast in soft elastomers to obtain stretchable and soft devices: a 2D stretchable resistive and capacitive sensor patterned with parallel metal lines, a 2D stretchable capacitive sensor patterned with an interdigitated metal structure with capacitive changes on stretching in both x - and y -axes, and a 3D compressive sensor by assembly of liquid metal helices, which could sense foot pressure compression. We also developed a facile method to interconnect between soft circuits and external electronics, suppressing stress during mechanical deformation.

Materials with a temperature-controlled reversible electrical transition between insulator and conductor are attracting huge attention due to their promising applications in many fields. However, most of them are intrinsically rigid and require complicated fabrication processes. Here, a highly stretchable (680% strain) liquid metal polymer composite as a reversible transitional insulator and conductor (TIC), which is accompanied with huge resistivity changes (more than 4 × 10 9 times) reversibly through a tuning temperature in a few seconds is introduced. When frozen, the insulated TIC becomes conductive and recovers after warming. Both the phase change of the liquid metal droplets and the rigidity change of the polymer contribute directly to transition between insulator and conductor. A simplified model is established to predict the expansion and connection of liquid metal droplets. Along with high stretchability, straightforward fabrication methods, rapid triggering time, large switching ratio, good repeatability, the TIC offers tremendous possibilities for numerous applications, like stretchable switches, semiconductors, temperature sensors, and resistive random-access memory. Accordingly, a system that can display numbers and letters via converting alternative TIC temperature to a binary signal on a computer is conceived and demonstrated. The present discovery suggests a general strategy for fabricating and stimulating a stretchable transitional insulator and conductor based on liquid metal and allied polymers., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)