A Robust Salty Water Adhesive by Counterion Exchange Induced Coacervate

Abstract

Counterion exchange of charged macromolecules has comprehensive implications in biological and synthetic systems such as protein function, biosignaling, ion conducting, and separation, but the correlation between the dynamic ion exchange, polyelectrolyte phase separation, and functionality remains elusive. Here, counterion exchange is exploited as a means to facilitate liquid–liquid phase separation and coacervates featuring higher stability and versatility compared with conventional complex coacervate. Self‐coacervation of a cationic polyelectrolyte (polyamidoamine‐epichlorohydrin, PAE‐Cl) occurs in broader conditions when its original counter anion (Cl−) is exchanged by bis(trifluoromethane‐sulphonyl)imide anion (TFSI−), as a result of TFSI− counter anions association instead of polyelectrolyte complexation. This coacervate is catechol‐free, easy to prepare, and highlights robust wet adhesion strength on diverse submerged surfaces in salty water (pH = 3–11), as demonstrated by its versatile capability of in situ underwater gluing and repairing without any pre‐immersive drying.

Rational design of adhesives for effective underwater bonding

“…When the temperature of water environment was elevated higher than the lower critical solution temperature of PNIPAM, this adhesive can transform to non-flowing hydrogels underwater. In addition, the covalent crosslinking that happened within the coacervate, such as the oxidation of catechol groups-induced crosslinking ( Shao and Stewart, 2010 ), azentidinium-induced crosslinking in base condition or over long time ( Wei et al, 2019 ; Zhu et al, 2019 ; Wang Z. et al, 2021 ) and [2 + 2] cycloaddition reaction of coumarincan-induced crosslinking ( Narayanan et al, 2020 ) also result in the curing of the coacervate-based adhesives. For these coacervate-based adhesives, the underwater adhesive strength was often higher than those of uncured coacervate-based adhesive, probably due to their stronger cohesiveness.…”

Recent Advances in Complex Coacervation Design from Macromolecular Assemblies and Emerging Applications

“…[ 131,132 ] Zhu et al. [ 133 ] investigated TFSI induced coacervation of cationic polyamidoamine‐epichlorohydrin (PAE‐Cl) arising in a broad processing window of pH and salt. The system exhibits instant wet adhesion because of abundant supramolecular interactions, and spontaneous curing by coupling reaction between azetinidium and secondary amine groups at basic pH, which could be finally endowed with adhesion strength as high as 400 kPa (Figure 16b).…”

Achieving strong, stable, and durable underwater adhesives based on a simple and generic amino-acid-resembling design

“…40,41 An alternative approach is to utilize the advantages of various common amino acids (CAAs) with non-catechol residues, which show more potential in diversified design directions and material alternatives. For example, inspired by the functionality in CAA pairs, several underwater adhesives based on electrostatic, 28,29 hydrophobic, 42,43 or cation-p associations 44,45 have been developed. However, these noncovalent associations exhibit weak and limited interaction sites that yield poor interfacial and bulk properties.…”