Design And Properties Of Functional Poly(Ionic Liquid) Adhesives

Adhesives,also known as industrial monosodium glutamate,are widely used in various fields.With the development of the social economy and the expansion of the market,the design of novel adhesives,the improvement of adhesive performance,and functional requirements are more and more important.At present,modern adhesives are mainly based on the catechol structure of dopamine and its derivatives.However,these materials are complex in synthesis,difficult to achieve functional design,dark in color,and cannot be recycled.Therefore,it is necessary to develop novel adhesives that are environmentally friendly and have better performance.In recent years,related researches indicate that in addition to hydrogen bonding interactions and van der Waals forces,noncovalent electrostatic interactions are also important for some adhesives.Nevertheless,the influence of electrostatic interaction on the adhesive mechanism and performance has not been revealed so far.Poly(ionic liquid)(PIL),which is a type of functional polymer with unique cationic and anionic characteristics in its structure,has shown several unique properties such as non-flammability,a wide electrochemical window,and high thermal stability.In this research,different kinds of PIL materials have been developed as efficient adhesives by balancing and improving the cohesive and interfacial adhesive interactions.The main contents and results are as follows:(1)To address the problems of the nonadhesive behavior of traditional PIL materials,highly adhesive material based on PIL(APIL)was fabricated by simply introducing alkoxy groups into the PILs containing bis(trifluoromethylsulfonyl)imide anions.The adhesion strength of APIL is related to its chemical structures,such as anion types,alkoxyl chain lengths,the presence of ionic groups,and quaternization degrees,all of which significantly influence adhesive performance.In addition,one of the APIL exhibits a unique and reversible response to electric fields,and the adhesive strength could be further improved in this process.The incorporated flexible alkoxy chain not only reduces the glass transition temperature of PILs but also endows these APIL materials with strong hydrogen bonding interactions,which,together with the unique electrostatic interaction,simultaneously contributes to high cohesive strength and interfacial adhesive strength.Consequently,these APIL materials are highly adhesive on various substrates,in contrast to the nonadhesive behavior of conventional PIL.(2)To address the problems of poor and limited organic solvent resistance of adhesives(including APIL),a zwitterionic poly(ionic liquid)(ZPIL)with a dynamic electrostatic cross-linking structure was developed as a novel adhesive material.The intermolecular interactions of traditional non-ionic polymers are much weaker,and most of them are easily swelled or even dissolved after soaking in organic solvents,generally resulting in adhesion failures.In contrast,the obtained ZPIL can overcome the solvation effect of organic solvent molecules on polymer chains by internal electrostatic cross-linking and a large number of non-covalent interactions.Consequently,these ZPIL materials are highly stable in their adhesive performance over a long time.(3)To simultaneously address the problems of complicated synthesis,high cost of PILs,and unbalanced cohesion and interfacial adhesion of adhesive applications,highly adhesive protic poly(ionic liquid)(PPIL)with strong organic solvent resistance are prepared by in-situ spontaneous polymerization.The initiator-free polymerization process was carried out through continuous evaporation of the solvent and a gradual increase in monomer concentration.After the polymerization process,a tough adhesive layer with highly entangled polymeric networks and an intimate interface contact between the adhesive and substrate was in-situ constructed.Abundant internal and external non-covalent interactions contribute to both cohesive strength and interfacial adhesive strength.In the aqueous solution,the polymer chains with the same charge tend to be more extended under the effect of electrostatic repulsion.With strong hydrogen bonding and electrostatic interactions,PPIL can effectively dissipate external forces.Consequently,these materials exhibited strong adhesion performance on various substrates.Moreover,the preparation of PPIL does not involve any volatile organic solvents or complex chemical synthesis processes,and have a low inherent cost,and is easy for large-scale applicated.(4)To address the problems of poor interfacial wetting,thick adhesive layer,serious resource waste,and limited application in flexible devices of conventional polymer adhesives,a supramolecular adhesive material based on ionic liquid(SIL)was designed by introducing ionic liquid moiety into a Y-shaped molecular with strong hydrogen bonding interactions.This kind of SIL material exhibits both high adhesion strength at room temperature and extraordinary temperature-sensitive rheological characteristics.At relatively high temperatures,the non-covalent interactions inside SIL are spontaneously destroyed,resulting in highly enhanced fluidity of the material,which can effectively wet the surface of the adhered material.The ionic liquid moiety not only improves the cohesive strength of the material through electrostatic interactions but also effectively inhibits the formation of rigid hydrogen bonding networks,releasing more hydrogen bonding donors/acceptors,and thereby improving interfacial adhesion strength.Consequently,these SIL materials exhibited highly adhesive features on various substrates.