Multifunctional Nanocomposite Yield-Stress Fluids for Printable and Stretchable Electronics.

Compliant materials are crucial for stretchable electronics. Stretchable solids and gels have limitations in deformability and durability, whereas active liquids struggle to create complex devices. This study presents multifunctional yield-stress fluids as printable ink materials to construct stretchable electronic devices. Ionic nanocomposites comprise silica nanoparticles and ion liquids, while electrical nanocomposites use the natural oxidation of liquid metals to produce gallium oxide nanoflake additives. These nanocomposite inks can be printed on an elastomer substrate and stay in a solid state for easy encapsulation. However, their transition into a liquid state during stretching allows ultrahigh deformability up to the fracture strain of the elastomer. The ionic inks produce strain sensors with high stretchability and temperature sensors with high sensitivity of 7% °C-1. Smart gloves are further created by integrating these sensors with printed electrical interconnects, demonstrating bimodal detection of temperatures and hand gestures. The nanocomposite yield-stress fluids combine the desirable qualities of solids and liquids for stretchable devices and systems.

Ultrastretchable MXene Microsupercapacitors.

Stretchable microsupercapacitors represent emerging miniaturized energy-storage devices for next-generation deformable electronics. Two-dimensional (2D) transition metal carbides (MXenes) are considered attractive electrode materials due to their metallic conductivity, hydrophilic surfaces, and excellent processability. Here, an ultrastretchable microsupercapacitor of interdigitated MXene microelectrodes with crumpled surface textures is created. The microsupercapacitor shows a series of attractive properties including a high specific capacitance of ≈185 mF cm-2 , ultrahigh stretchability up to 800% area strain, and ≈89.7% retention of the initial capacitance after 1000 stretch-relaxation cycles. In addition to static strains, the microsupercapacitor demonstrates robust mechanical properties to retain stable charging-discharging capability under dynamic stretching at different strain rates. A self-powering circuit system utilizes four microsupercapacitor packs to power a light-emitting diode (LED) array, which exhibits stable operations under large tensile strain and skin-attached wearable settings. The developments offer a generic design strategy to enhance the deformability of microsupercapacitors based on 2D nanomaterials.

A Highly Stretchable and Permeable Liquid Metal Micromesh Conductor by Physical Deposition for Epidermal Electronics.

Stretchable electronics allow functional devices to integrate with human skin seamlessly in an emerging wearable platform termed epidermal electronics. Compliant conductors represent key building components for functional devices. Among the various candidates, gallium-based liquid metals stand out with metallic conductivity and inherent deformability. Currently, the widespread applications of liquid metals in epidermal electronics are hindered by the low steam permeability and hence unpleasant wearing perceptions. In this study, a facile physical deposition approach is established to create a liquid metal micromesh over an elastomer sponge, which exhibits low sheet resistance (∼0.5 Ω sq-1), high stretchability (400% strain), and excellent durability. The porous micromesh shows textile-level permeability to achieve long-term wearing comfort. The conformal interaction of the liquid metal micromesh with the skin gives rise to a low contact impedance. An integrated epidermal sensing sleeve is demonstrated as a human-machine interface to distinguish different hand gestures by recording muscle contractions. The reported stretchable and permeable liquid metal conductor shows promising potentials in next-generation epidermal electronics.

Crumpled MXene Electrodes for Ultrastretchable and High-Area-Capacitance Supercapacitors.

In spite of the excellent electrical and electrochemical properties, two-dimensional transition metal carbide (MXene) is often limited by the high stiffness for the direct implementation in next-generation stretchable and wearable energy storage devices. The improved deformability has been achieved in ultrathin composite electrodes utilizing additives that substantially reduce the specific capacitance. Here, we demonstrate an ultrastretchable and high-performing supercapacitor based on MXene electrodes with crumpled textures. After screening on the thickness, the crumpled MXene film of ∼3 µm in thickness is identified as the optimal choice to mitigate the crack formations under large and repetitive mechanical strains. The as-prepared symmetric supercapacitor, therefore, demonstrates a high specific capacitance of ∼470 mF cm-2, ultrahigh stretchability up to 800% area strain, and >90% retention of the initial capacitance after 1000 stretch-relaxation cycles. The developments offer an attractive avenue to design stretchable electrodes based on various two-dimensional nanomaterials and their composites.

Printable Liquid Metal Microparticle Ink for Ultrastretchable Electronics.

Liquid metal confined in the elastomer represents an ideal platform for stretchable electronics with ultimate deformability. To enable facile and scalable patterning of conductive features, bulk liquid metal is typically dispersed into fine particles to formulate printable inks. The presence of native oxide or organic ligands stabilizing these liquid metal particles unfortunately inhibits their direct coalescence to recover the metallic conductivity and liquid-state deformability. Here, we report a chemical sintering process that converts printed liquid metal microparticles into a highly deformable conductor. The process involves the removal of surface passivating oxide by a short exposure to acid fume and subsequent selective wetting of liquid metal microparticles onto copper nanoplates present in the ink formulation. The chemical reaction provides the basis for a facile and scalable procedure to print conductive features over a large area with exceptional conductivity (>104 S cm-1) and ultrahigh stretchability (∼1000% strain). Their practical suitability is demonstrated by the fabrication of an ultrastretchable ribbon cable and an epidermal heater.

Maskless Patterning of Biodegradable Conductors by Selective Laser Sintering of Microparticle Inks and Its Application in Flexible Transient Electronics.

Biodegradable electronic devices are able to break down into benign residues after their service life, which may effectively alleviate the environmental impacts as a consequence of the proliferation of consumer electronic technology. The widespread adaptation to biodegradable systems is currently impeded by the lack of economic fabrication techniques for functional devices. Here, a facile approach to generate a biodegradable conductor is developed based on selective laser sintering of zinc and iron microparticle ink. The sintering process is effective to convert naturally oxidized microparticles into interconnected conductors. Arbitrary conductive features are readily created over flexible biodegradable substrates under ambient conditions, which exhibits excellent conductivity (∼2 × 106 S m-1), low sheet resistance (∼0.64 Ω â–¡ - 1), fine feature resolution (∼45 µm), and mechanical flexibility. The practical suitability is demonstrated by fabricating a miniaturized near-field communication tag with the dimension to mount on the fingernail. The methodology is further extended to create a metallic grid as a biodegradable transparent electrode with low sheet resistance (2.5 Ω â–¡-1) and high optical transmittance (96%), which is employed as an epidermal transparent heater for thermotherapy. Maskless patterning of biodegradable conductors may find a broad range of applications in environment friendly gadgets and implantable medical devices.

Rapid, all dry microfabrication of three-dimensional Co3O4/Pt nanonetworks for high-performance microsupercapacitors.

On-chip electrochemical energy storage devices have attracted growing attention due to the decreasing size of electronic devices. Various approaches have been applied for constructing the microsupercapacitors. However, the microfabrication of high-performance microsupercapacitors by conventional and fully compatible semiconductor microfabrication technologies is still a critical challenge. Herein, unique three-dimensional (3D) Co3O4 nanonetwork microelectrodes formed by the interconnection of Co3O4 nanosheets are constructed by controllable physical vapor deposition combined with rapid thermal annealing. This construction process is an all dry and rapid (≤5 minutes) procedure. Afterward, by sputtering highly electrically conductive Pt nanoparticles on the microelectrodes, the 3D Co3O4/Pt nanonetworks based microsupercapacitor is fabricated, showing a high volume capacitance (35.7 F cm-3) at a scan rate of 20 mV s-1 due to the unique interconnected structures, high electrical conductivity and high surface area of the microelectrodes. This microfabrication process is also used to construct high-performance flexible microsupercapacitors, and it can be applied in the construction of wearable devices. The proposed strategy is completely compatible with the current semiconductor microfabrication and shows great potential in the applications of the large-scale integration of micro/nano and wearable devices.