Soft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated.

A new graphene-fullerene composite (rGO-pyrene-PCBM), in which [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was attached onto reduced graphene oxide (rGO) via the noncovalent functionalization approach, was reported. The pyrene-PCBM moiety was synthesized via a facile esterification reaction, and pyrene was used as an anchoring bridge to link rGO and PCBM components. FTIR, UV-vis, and XPS spectroscopic characterizations were carried out to confirm the hybrid structure of rGO-pyrene-PCBM, and the composite formation is found to improve greatly the dispersity of rGO in DMF. The geometric configuration of rGO-pyrene-PCBM was studied by Raman, SEM, and AFM analyses, suggesting that the C60 moiety is far from the graphene sheet and is bridged with the graphene sheet via the pyrene anchor. Finally rGO-pyrene-PCBM was successfully applied as electron extraction layer for P3HT:PCBM bulk heterojunction polymer solar cell (BHJ-PSC) devices, affording a PCE of 3.89%, which is enhanced by ca. 15% compared to that of the reference device without electron extraction layer (3.39%). Contrarily, the comparative devices incorporating the rGO or pyrene-PCBM component as electron extraction layer showed dramatically decreased PCE, indicating the importance of composite formation between rGO and pyrene-PCBM components for its electron extraction property.

Future wearable technologies and personal electronics may benefit from e‐textiles that simultaneously possess high elasticity and multiple capabilities such as energy harvesting and sensing. Here, the first elastic multifunctional fiber that can scavenge mechanical energy from body motion and electromagnetic energy from surrounding electrical appliances is presented. In addition to converting multiple sources of waste energy into electricity, the fibers can also serve as self‐powered tactile and biomechanical sensors. The fibers consist of hollow elastomeric fibers filled with liquid metal. The fibers harvest energy by the combination of triboelectricity (160 V m−1, 5 µA m−1, and ≈360 µW m−1) and induced electrification of the liquid metal (±8 V m−1 (60 Hz), ±1.4 µA m−1, and ≈8 µW m−1). The fibers are characterized and their utility for powering electronics and sensing biomechanical information is demonstrated. These fibers are further demonstrated as completely soft and stretchable components for human–machine interfaces, including keypads and wireless music controllers.

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Fabrics are widely used in hospitals and many other settings for bedding, clothing, and face masks; however, microbial pathogens can survive on surfaces for a long time, leading to microbial transmission. Coatings of metallic particles on fabrics have been widely used to eradicate pathogens. However, current metal particle coating technologies encounter numerous issues such as nonuniformity, processing complexity, and poor adhesion. To overcome these issues, an easy‐to‐control and straightforward method is reported to coat a wide range of fabrics by using gallium liquid metal (LM) particles to facilitate the deposition of liquid metal copper alloy (LMCu) particles. Gallium particles coated on the fabric provide nucleation sites for forming LMCu particles at room temperature via galvanic replacement of Cu2+ ions. The LM helps promote strong adhesion of the particles to the fabric. The presence of the LMCu particles can eradicate over 99% of pathogens (including bacteria, fungi, and viruses) within 5 min, which is significantly more effective than control samples coated with only Cu. The coating remains effective over multiple usages and against contaminated droplets and aerosols, such as those encountered in facemasks. This facile coating method is promising for generating robust antibacterial, antifungal, and antiviral fabrics and surfaces.

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