Stretchable and negative-Poisson-ratio porous metamaterials

Simultaneous high strength and high toughness are highly sought‐after in lattice metamaterials, but these properties are typically mutually exclusive. To overcome this challenge, the development of interpenetrating phase composite (IPC), which incorporates a net matrix infill into the lattice, has shown great potential in overcoming these constraints and is thus of continuous practical interest. In this work, a novel aperiodic monotile truss lattice and polymer IPC that exhibit unprecedented enhancement in both strength and toughness are reported. Specifically, the aperiodic unit cell is inspired by Einstein's monotile, a single space‐filling shape where the cell orientation never repeats. The IPCs are achieved through 3D‐printed Ti‐6Al‐4V truss lattices and epoxy infiltration. The highest gain in compressive strength reveals an impressive 246.61% increase, significantly exceeding the “1 + 1 > 2” idealization typically associated with strength in IPC metamaterials. Furthermore, a high specific energy absorption of 46.2 J g−1 demonstrates superior toughness. The underlying mechanisms, including damage sequences, two‐phase interactions, and geometric effects between truss and epoxy, are fully elucidated. Overall, this work reports unprecedented enhancement in IPC's properties and demonstrates the potential of utilizing idealized structures to achieve an optimal combination of strength and toughness in mechanical metamaterials.

Unprecedented Strength Enhancement Observed in Interpenetrating Phase Composites of Aperiodic Lattice Metamaterials

Wang,

Li,

Deng

et al. 2024

Advanced Stretchable Aerogels and Foams for Flexible Electronics and Beyond

Liang,

Sun,

Zhang

et al. 2024

With the increasing demands for artificial intelligence, robotics, electronic skin, healthcare, and energy storage/conversion, the research focus on flexible electronics has started to shift from being merely bendable and rollable to being stretchable. In recent years, stretchable aerogels and foams have drawn significant attention in the field of flexible electronics due to their unique porous structures, low density, high porosity, and high flexibility. This work provides a comprehensive review of the state‐of‐the‐art developments in stretchable aerogels and foams, encompassing their preparation, structures, properties, and applications. The preparation methods, typical structures of stretchable aerogels and foams, stretching principle, and the relationship between their structures, stretchability, and other properties are investigated. Their latest applications in stretchable strain/pressure sensors, electrodes and conductors, chemical sensors and biosensors, supercapacitors, batteries, triboelectric nanogenerators, electromagnetic shielding, microwave absorption, thermal management, adsorption, separation/filtration, and shape memory are introduced. Furthermore, the challenges and opportunities of stretchable aerogels and foams are summarized. This work provides a guideline for the development of stretchable aerogels and foams and next‐generation high‐performance flexible electronics based on stretchable porous materials.

Highly Stretchable Supercapacitor‐Type Multifunctional Self‐Powered Porous Electronic Skins

Zhang,

Wang,

Liang

et al. 2024

The development of highly stretchable self‐powered electronic skins with a broad detection range is urgently needed but remains a great challenge. Herein, unprecedented highly stretchable, broad‐range‐response, supercapacitor‐type, one‐body, and self‐powered electronic skins are developed by assembling porous polyurethane/polypyrrole electrode, polyacrylic acid/polyacrylamide ionic gel electrolyte, and porous polyurethane/MXene electrode. The folded porous structure of the electrodes significantly enhances the stretchability, while the modulus‐gradient multilayer structure of the device effectively broadens the pressure detection range. The electronic skins combine self‐powered dynamic/static pressure sensing, ultrabroad detection range (20 Pa–3.5 MPa), ultrahigh stretchability up to 387%, excellent compression stability (5000 cycles under 195 kPa), and good stretching stability (500 cycles under 200% tensile strain). They have the capability of monitoring human body motions, physiological signals, and high pressures from motorcycle tires, as well as tactile sensing of robotic grippers. In addition, they can be applied for highly stretchable thermal management and electromagnetic shielding devices. This work provides a new strategy for the development of highly stretchable, broad‐range‐response, and multifunctional self‐powered wearable electronics and sensors.