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A design for a metamaterial with tunable stiffness is introduced. The material can be switched from floppy to rigid by changing the lengths of the constituent beams, which is demonstrated using a temperature-responsive hydrogel. 

Logic gates (AND, OR, and NOT) have been demonstrated at the air–water interface by using light-driven thermocapillary actuation of microscale particles. 

Anionic polymerized ionic liquids with a fixed sulfonylimide group have emerged as promising materials for energy storage applications, electromechanical devices, and gas separation membranes due to their highly delocalized anionic charges. However, synthetic challenges have limited the production of high-purity poly(sulfonylimide)s at scale and hindered systematic evaluation of their properties. We report a synthetic route for the production of high-purity sulfonylimide monomers at >10 g scales using a sulfur(VI) fluoride exchange (SuFEx) click reaction. Pendent sulfonylimide acrylate monomers with 1-ethyl-3-methylimidazolium counterions were synthesized with perfluorinated side groups of different lengths and cross-linked to form ionoelastomers. The networks were stretchable (≈120% strain at break), showed high solvent-free ionic conductivity (>3.8 × 10–3 mS/cm), and were hydrophobic with water contact angles >105°. The imidazolium counterions interact strongly with the perfluorinated side chains, yielding nonmonotonic trends in ionic conductivity and modulus relative to the glass transition temperature (Tg). Wide-angle X-ray scattering and vibrational spectroscopies reveal that shorter perfluorinated side groups promote cation dissociation, while longer chains cause ionic aggregation. We expect that this SuFEx approach will expand access to next-generation poly(sulfonylimide) electrolytes for a variety of applications and here demonstrate its utility for providing new insight into the molecular-level design of poly(sulfonylimide) ionoelastomers. 

Self-folding origami, structures that are engineered flat to fold into targeted, three-dimensional shapes, have many potential engineering applications. Though significant effort in recent years has been devoted to designing fold patterns that can achieve a variety of target shapes, recent work has also made clear that many origami structures exhibit multiple folding pathways, with a proliferation of geometric folding pathways as the origami structure becomes complex. The competition between these pathways can lead to structures that are programmed for one shape, yet fold incorrectly. To disentangle the features that lead to misfolding, we introduce a model of self-folding origami that accounts for the finite stretching rigidity of the origami faces and allows the computation of energy landscapes that lead to misfolding. We find that, in addition to the geometrical features of the origami, the finite elasticity of the nearly-flat origami configurations regulates the proliferation of potential misfolded states through a series of saddle-node bifurcations. We apply our model to one of the most common origami motifs, the symmetric “bird's foot,” a single vertex with four folds. We show that though even a small error in programmed fold angles induces metastability in rigid origami, elasticity allows one to tune resilience to misfolding. In a more complex design, the “Randlett flapping bird,” which has thousands of potential competing states, we further show that the number of actual observed minima is strongly determined by the structure's elasticity. In general, we show that elastic origami with both stiffer folds and less bendable faces self-folds better. 

Formation of desired three-dimensional (3D) shapes from flat thin sheets with programmed non-uniform deformation profiles is an effective strategy to create functional 3D structures. Liquid crystal elastomers (LCEs) are of particular use in programmable shape morphing due to their ability to undergo large, reversible, and anisotropic deformation in response to a stimulus. Here we consider a rectangular monodomain LCE thin sheet divided into one high- and one low-temperature strip, which we dub a ‘bistrip’. Upon activation, a discontinuously patterned, anisotropic in-plane stretch profile is generated, and induces buckling of the bistrip into a rolled shape with a transitional bottle neck. Based on the non-Euclidean plate theory, we derive an analytical model to quantitatively capture the formation of the rolled shapes from a flat bistrip with finite thickness by minimizing the total elastic energy involving both stretching and bending energies. Using this analytical model, we identify the critical thickness at which the transition from the unbuckled to buckled configuration occurs. We further study the influence of the anisotropy of the stretch profile on the rolled shapes by first converting prescribed metric tensors with different anisotropy to a unified metric tensor embedded in a bistrip of modified geometry, and then investigating the effect of each parameter in this unified metric tensor on the rolled shapes. Our analysis sheds light on designing shape morphing of LCE thin sheets, and provides quantitative predictions on the 3D shapes that programmed LCE sheets can form upon activation for various applications.