Self-Healable and 4D Printable Hydrogel for Stretchable Electronics.

Materials with high stretchability and conductivity are used to fabricate stretchable electronics. Self-healing capability and four-dimensional (4D) printability are becoming increasingly important for these materials to facilitate their recovery from damage and endow them with stimuli-response properties. However, it remains challenging to design a single material that combines these four strengths. Here, a dually crosslinked hydrogel is developed by combining a covalently crosslinked acrylic acid (AAC) network and Fe3+ ions through dynamic and reversible ionically crosslinked coordination. The remarkable electrical sensitivity (a gauge factor of 3.93 under a strain of 1500%), superior stretchability (a fracture strain up to 1700%), self-healing ability (a healing efficiency of 88% and 97% for the mechanical and electrical properties, respectively), and 4D printability of the hydrogel are demonstrated by constructing a strain sensor, a two-dimensional touch panel, and shape-morphing structures with water-responsive behavior. The hydrogel demonstrates vast potential for applications in stretchable electronics.

Molecular Insights into the Composition-Structure-Property Relationships of Polyamide Thin Films for Reverse Osmosis Desalination.

A molecular-level understanding of the structure-property relationship of polyamide (PA) active layers in thin-film-composite membranes remains unclear. We developed an approach to build and hydrate the PA layer in molecular dynamics simulations and reproduced realistic membrane properties, which enabled us to examine the composition-structure-permeability relationships at the molecular level. We discovered the variation of pore size distributions in the dry PA structures at different monomer compositions, leading to different water cluster distributions and wetting properties of hydrated PA films. Membrane swelling was linearly dependent on the degree of cross-linking (DC), and higher water flux was obtained in the more swelling-prone PA films because of the transition in water transport mechanisms. Continuum-like and jumping transport both occurred in PA films with smaller DC, where visible and more persistent channels existed. In the denser films, water molecules relied only on the on-and-off channels to jump from one cavity to another; however, jumping transport was more pronounced even in the less dense PA films, and all the PA structures exhibited oscillations, which provided evidence for the solution-diffusion model rather than the pore-flow model. The results not only contribute to fundamental understanding but also provide insights into the molecule-level design for next-generation membranes.