Reversible fiber fusion and fission: Materials that can cycle between states are of interest for actuators, soft robotics, or recoverable membranes for separations. Chang et al. show that a collection of graphene oxide fibers can fuse into a single stronger fiber upon immersion in a solvent, extraction, and drying under tension (see the Perspective by Cruz-Silva and Elías). The geometrical deformation of the fibers during drying and swelling plays an important role in the reversible cycles, with a large volume change between the dried and swelled fibers. Moreover, fibers made from polymers, glass, metal, or silk can be given these abilities when coated with a micron-sized layer of graphene oxide. Science , this issue p. 614 ; see also p. 573

The complex sequential response of frustrated materials results from the interactions between material bits called hysterons. Hence, a central challenge is to understand and control these interactions, so that materials with targeted pathways and functionalities can be realized. Here, we show that hysterons in serial configurations experience geometrically controllable antiferromagnetic-like interactions. We create hysteron-based metamaterials that leverage these interactions to realize targeted pathways, including those that break the return point memory property, characteristic of independent or weakly interacting hysterons. We uncover that the complex response to sequential driving of such strongly interacting hysteron-based materials can be described by finite state machines. We realize information processing operations such as string parsing in materia, and outline a general framework to uncover and characterize the FSMs for a given physical system. Our work provides a general strategy to understand and control hysteron interactions, and opens a broad avenue toward material-based information processing.

Pristine graphene is one of the strongest materials known in the world, and may play important roles in structural and functional materials. In order to utilize the extraordinary mechanical properties in practical engineering structures, graphene should be assembled into macroscopic structures such as graphene-based papers, fibers, foams, etc. However, the mechanical properties of graphene-based materials such as Young’s modulus and strength are 1–2 orders lower than those of pristine monolayer graphene. Many efforts have been made to unveil the multi-scale structure–property relations of graphene-based materials with hierarchical structures spanning the nanoscale to macroscale, and significant achievements have been obtained to improve the mechanical performance of graphene-based materials through composition and structure optimization across multi-scale. This review aims at summarizing the currently theoretical, simulation, and experimental efforts devoted to the multi-scale structure–property relation of graphene-based layer materials including defective monolayer graphene, nacre-like and laminar nanostructures of multilayer graphene, graphene-based papers, fibers, aerogels, and graphene/polymer composites. The mechanisms of mechanical property degradation across the multi-scale are discussed, based on which some multi-scale optimization strategies are presented to further improve the mechanical properties of graphene-based layer materials. We expect that this review can provide useful insights into the continuous improvement of mechanical properties of graphene-based layer materials.

In this work, the surface wrinkle modulation of the film/substrate system caused by eigenstrain in the film is studied. A theoretical model is proposed which shows the change of the wrinkle amplitude is completely determined by four dimensionless parameters, i.e., the eigenstrain in the film, the plane strain modulus ratio between the film and the substrate, the film thickness to wrinkle wavelength ratio, and the initial wrinkle amplitude to wavelength ratio. The surface wrinkle amplitude becomes smaller (even almost flat) for the contraction eigenstrain in the film, while for the expansion eigenstrain it becomes larger. If the expansion eigenstrain exceeds a critical value, secondary wrinkling on top of the existing one is observed for some cases. In general, the deformation diagram of the wrinkled film/substrate system can be divided into three regions, i.e., the change of surface wrinkle amplitude, the irregular wrinkling, and the secondary wrinkling, governed by the four parameters above. Parallel finite element method (FEM) simulations are carried out which have good agreement with the theoretical predictions. The findings may be useful to guide the design and performance of stretchable electronics, cosmetic products, biomedical engineering, soft materials, and devices.

Despite 10% of the Earth’s surface being covered by ice, ice power remains untapped. Although ice is known to generate electricity upon bending via flexoelectricity¹, the generated electric polarization per curvature, that is, the flexoelectric coefficient, is too small (~1–10 nC m⁻¹) to be utilized for electromechanical devices. Here we demonstrate that doping ice with NaCl can enhance its flexoelectric coefficient 1,000-fold, to ~1–10 μC m⁻¹. We find that this enhancement is due to the bending-induced streaming current along ice grain boundaries. On the basis of this mechanism, we fabricated flexural devices with an effective piezoelectric coefficient of ~4,000 pC N⁻¹, which is comparable to that of the best piezoelectric materials. The high flexoelectricity of saline ice brings the vision of harnessing ice power one step closer to reality, and may also be relevant to the electrical activity of ice-covered terrestrial regions and icy ocean worlds such as Europa or Enceladus. In addition, the model for coupling between strain gradients and streaming currents is not limited to ice and provides a general framework for extracting electromechanical activity from liquid-infused porous solids.