Bioinspired Integrated Auxetic Elastomers Constructed by a Dual Dynamic Interfacial Healing Strategy

Abstract

Auxetic materials are appealing due to their unique characteristics of transverse expansion while being axially stretched. Nevertheless, current auxetic materials are often produced by the introduction of diverse geometric structures through cutting or other pore‐making processes, which heavily weaken their mechanical performance. Inspired by the skeleton‐matrix structures in natural organisms, here we report an integrated auxetic elastomer (IAE) composed of high‐modulus crosslinked poly(urethane‐urea) as a skeleton and low‐modulus non‐crosslinked poly(urethane‐urea) as a complementary‐shape matrix. Benefiting from disulfide bonds and hydrogen bonds‐promoted dual dynamic interfacial healing, the resulting IAE is flat, void‐free, and has no sharp soft‐to‐hard interface. Its fracture strength and elongation at the break are increased to 400% and 150%, respectively, of the values of corrugated re‐entrant skeleton alone, while the negative Poisson's ratio (NPR) reserves within a strain range of 0–104%. In addition, the advantageous mechanical and auxetic properties of this elastomer are further confirmed by finite element analysis. The concept of combining two dissimilar polymers into an integrated hybrid material solves the problem of the deterioration in mechanical performance of auxetic materials after subtractive manufacturing, while preserves the NPR effect in a large deformation, which provides a promising approach to robust auxetic materials for engineering applications.This article is protected by copyright. All rights reserved

Ultrastable, Superrobust, and Recyclable Supramolecular Polymer Networks

“…Although the 1D supramolecular polymers generally suffer from low mechanical robustness, such a brilliant concept drives the advancement of adaptive, responsive, and reorganizable polymeric materials that are healable, reprocessable, and recyclable, thanks to the dynamic and reversible nature of noncovalent bonds [6–16] . In this scenario, crosslinking macromolecules by abundant noncovalent bonds to form 3D supramolecular polymer networks (SPNs) has emerged as an alternative paradigm for the design of mechanically robust polymeric materials with dynamic and reversible properties [17–48] . Nevertheless, the advantageous dynamic nature of noncovalent bonds conversely results in poor stability of SPNs, which significantly plagues their practical utility as reliable and sustainable materials in human activities and engineering applications.…”

Molecular Auxetic Polymer of Intrinsic Microporosity via Conformational Switching of a Cavitand Crosslinker

“…As an alternative, continuous composites with properly organized soft or hard inclusions have been shown to be auxetic. [6,7] The first theoretical model of an isotropic and thermodynamically stable molecular auxetic was published in 1987 by Wojciechowski, [8] foreseeing a NPR for a planar (2D) model of hard cyclic hexamers. [9] Afterward, inspired by macroscopic re-entrant honeycomb and rotating triangle structures, molecular auxetic behavior has been theoretically predicted for a variety of molecular networks constituted by "twisted-chain" polyacetylenes, [10] crosslinked rigid polyphenylacetylenes, [11] calix [4]arene-based polymeric network [12] and prismane-based molecular rods.…”