Transparent, Healable Elastomers with High Mechanical Strength and Elasticity Derived from Hydrogen-Bonded Polymer Complexes

Abstract

It is challenging to develop healable elastomers with combined high mechanical strength and good elasticity. Herein, a simple strategy to develop high-performance elastomers that integrate high mechanical strength, enormous stretchability, good resilience, and healability is reported. Through simply complexing poly(acrylic acid) and poly(ethylene oxide) based on hydrogen-bonding interactions, transparent composite materials that perform as elastomers are generated. The as-prepared elastomers exhibit mechanical strength (true strength at break) and toughness (fracture energy) as high as 61 MPa and 22.9 kJ/m, respectively, and they can be stretched to >35 times their initial length and are able to return to their original dimensions following the removal of stress. Further, the elastomers are capable of healing from physical cuts/damages in a humid environment because of reformation of the reversible hydrogen bonds between the polymer components. The high mechanical strength of the elastomers is ascribed to the high degree of polymer chain entanglements and multiple hydrogen-bonding interactions in the composites. The reversible hydrogen bonds, which act as cross-linkages, facilitate the unfolding and sliding of the polymer chains in the composites, thereby endowing the elastomers with good elasticity and healability. Furthermore, flexible conductors with water-enabled healability were developed by drop-casting Ag nanowires on top of the elastomers.

Mechanically Strong and Highly Stiff Supramolecular Polymer Composites Repairable at Ambient Conditions

“…Notably, these healable hydrated or elastic polymer complex-based materials are all soft and deformable with tensile strengths lower than 10 MPa. 25,26,63,65 In our present work, we demonstrate that the highly rigid PAA-PAH supramolecular composite (σ = 67 MPa and E = 2.0 GPa) could be repaired by simply employing the PAA-PAH coacervate as the healing agent under ambient conditions (25 o C; 40% relative humidity). The healing strategy reported here provides a supplementary method for a simple repair of highly rigid materials that comprise noncovalently bonded components.…”

“…The PAA-PEO elastomer was prepared according to our previous report. 63 Briefly, aqueous solutions of PAA (M w of 450,000, 4 mg mL −1 , pH 2.5) and PEO (M w of 600,000, 4 mg mL −1 , pH 2.5) were mixed under stirring at the PAA:PEO volume ratio of 1.6∶1.0, the feed monomer molar ratio between PAA and PEO is 1.0∶1.0. The precipitates of PAA-PEO complexes was formed instantaneously under our established ambient conditions at room temperature, and the resultant precipitate was collected by centrifugation, followed by compression molding for 2 days via two pieces of glass slides at a pressure of ∼ 15 kPa.…”

“…This is because water or salt swelling could not activate diffusion of the polymer chains across the fracture of the PAA 1.6 -PAH 1.0 composite. Further, the PAA-PAH coacervate was applied to repair other fractured supramolecular polymer composites, such as our previously reported elastomer derived from the H-bonded PAA-poly(ethylene oxide) (PAA-PEO) complexes (Figure 5c) 63 . As shown in Figure 5d, the tensile strength attained by the repaired elastomer was up to 100% recovery of the pristine value of the sample.…”

“…Recently, polymer complexation has become a simple emerging method to fabricate bulk supramolecular composite materials with tailored compositions and functions. 25,26,[60][61][62][63][64][65] Due to the existence of high-density reversible noncovalent interactions, materials derived from polymer complexes are potentially healable, while implementation of the healing function has to meet the three prerequisites described earlier. Previous reports from our lab and labs of other groups demonstrated that materials of polymer complexes, in the hydrated (i.e., hydrogel) 25, 26,65 or elastomeric 63 state, exhibited intrinsic healing behaviors by the assistance of water or salt swelling.…”

Room‐Temperature Self‐Healing and Recyclable Tough Polymer Composites Using Nitrogen‐Coordinated Boroxines

“…In recent decades, scientific interest in intrinsic self‐healing materials has increased tremendously because of their enhanced reliability and their ability to be healed multiple times . The potential applications of these materials can be found in thermoreversible rubbers, thermoplastic elastomers, mechanically enhanced hydrogels, electrically conductive materials, semiconducting polymers for organic transistors, electronic skins, and so forth. Dynamic covalent bonds have been frequently used for the fabrication of mechanically improved self‐healing polymer composites because they can integrate the robustness of covalent bonds and the intrinsic reversibility of noncovalent physical interactions .…”