Underwater Curing Of Polyelectrolyte Coacervate And Wet Adhesion Properties

Wet adhesion is indispensable to various applications spanning from surgery closure,underwater fixing to aqueous coating and surface engineering.However,the development of robust underwater adhesives is challenging because the water molecules absorbed at surface of targeted substrates and thus diminish their interactions with the wet adhesives.To date,the coacervates that mimick the excretion of marine creatures,i.e.sandcastle worms and mussels,represent the mosteffective adhesives at various wet conditions.The formation,transportion and solidification of water-immiscible coacervates all determine the adhesion strengths.Despite those progresses,the underwater curing of synthetic coacervates still remains technically challenged.For example,catechol crosslinking is the state-of-the-art curing method for coacervate,which suffers from sophisticated synthesis of catechol-containing polymers and inefficient curing as a result of uncontrolled oxidation.To this end,this work focuses on the novel curing chemistry facilitating underwater curing of coacervates,with an aim for advanced wet adhesion.First,a waterborne and catechol-free strategy were proposed to prepare robust underwater adhesives by exploiting biomass pulping residues,lignosulfonate(LS),and an economic industrial additive,polyamidoamine-epichlorohydrin(PAE-Cl).Fluidic coacervates were attained by modulating the complexation conditions between PAE and LS.The LS-PAE coacervate allows for instant underwater adhesion to various substrates.More importantly,it enables spontaneous underwater self-curing that substantially improves wet adhesion strength.As such,the wet adhesion was stable against p H(p H 6-10),salt concentration(1.0 M Na Cl),high temperature(100°C),and long-time soaking(30 days).Second,a random copolymer,i.e.,poly(1-benzyl-3-vinylimidazolium)-co-(1-vinyl-3-ethylamine imidazolium)(P-Ben-CN),was designed for self-coacervation and self-curing in deep sea.In this design,the aromatic monomer and nitrile monomer confer salt-triggered coacervation and p H-modulated responsive crosslinking to the copolymer system,respectively.Unlike catechol oxidation and ring-opening reaction of PAE,the P-Ben-CN coacervate features higher efficacy cyclization of nitrile,independent of oxidative conditions and high temperature.As such,the P-Ben-CN is curable in deep sea water which is～3 ~oC and oxygen depleted,leading to promising pull-off adhesion strength of 0.3 MPa.This work provides valube guidance for designing novel wet adhesives targeting deep sea scenarios that are less explored.