Multifunctional Supramolecular Adhesives With High Bonding Strength

Adhesives are used ubiquitously in our daily life and industrial felds due to their ability to easily bond substrates.High bonding strength on various substrates is always an important goal in the research of the adhesives.Reversible adhesion is also desirable property of the adhesives for practical applications.Such adhesives have the ability to reversibly de-bond from a substrate and then re-bond with minimal loss of bonding strength between de-bonding/re-bonding cycles.However,reversible adhesion requires adhesives to be soft to maximize contact area while simultaneously maintaining stiffness in the direction of loading to maximize the bonding performance,which are conflicting characteristics.Therefore,it is a challenge to fabricate adhesives that exhibit high bonding strength and reversible adhesion.Moreover,the adhesion in wet environments(under water and seawater)is an important concern for many constructions and marine applications.However,the adhesion is especially difficult to achieve in the presence of water,because water as a boundary layer can weaken the interfacial adhesion of the adhesive and as a solvent can undermine the integrity of the adhesive.This is the reason why synthetic adhesives developed for dry applications perform poorly in wet environments.In this context,there is a rapidly growing interest in the development of adhesives with high bonding strength and good ability in both dry and wet environments.In addition,it is important to design adhesives to meet the high bonding strength and functional recovery of specific substrate materials,which can further promote the development of the adhesives.Herein,a variety of supramolecular adhesives were developed by incorporation of numerous noncovalent interactions.By exquisitely regulating the viscoelastic properties of the adhesives,the adhesive and cohesive strength of the adhesives can be well balanced.The supramolecular adhesive exhibits high bonding strength to a variety of substrates.Moreover,due to the diversity and reversible ability of the noncovalent interactions,the supramolecular adhesive also exhibits reversible and underwater adhesion.The adhesives exhibit good ability in both dry and wet environments.In addition,we also developed a coacervate adhesive to repair the highly rigid material at the ambient condition based on noncovalent interactions.The main contents are as follows:1.Taking advantages of the good wetting ability and non-volatility of ionic liquids,ionogel adhesives are prepared by blending an imidazolium-based ionic liquid with a copolymer bearing charged quaternary amine groups.By regulating the viscoelastic properties of the ionogel,the adhesive and cohesive strength of the ionogel can be well balanced to maximize the bonding strength.The as-developed ionogel exhibits high bonding strength(>0.3 MPa)for PTFE,plastics,metal,wood and glass,because the variety of functional groups in the ionogel can form various supramolecular interactions with different substrates.In particular,the ionogel also exhibits reversible,easy-release and reusable properties for multiple times of bonding and on-demand debonding without leaving obvious residues on the substrates.2.We report an adhesive that offer excellent adhesion ability to diverse substrates for aqueous and dry conditions.The adhesive consists of a copolymer of acrylic acid(AA)and butyl acrylate(BA).In the adhesive,the numerous hydrogen bonds of the AA units introduce high cohesion to the adhesive,while the BA units generate the formation of the hydrophobic interaction underwater.In the underwater adhesion,the BA units in the adhesive can repel the water molecules in the surface of the substrate,then the adhesive is able to achieve effective contact with the substrate underwater.The adhesive was found to exhibit excellent adhesion to both hydrophilic and hydrophobic substrates under water/artificial seawater,the adhesive strength of the adhesive to Glass,SS,PET(polyethylene glycol terephthalate),PP(polypropylene),PVC(polyvinyl chloride),PMMA(polymethyl methacrylate),PTFE(polytetrafluoroethylene)underwater is all above 100k Pa.The adhesive can also adhere well to diverse substrate in air,the peeling adhesion strength between the adhesive and diverse substrates in air was observed above 304.9 N m^-1.In particular,the adhesive also exhibited excellent underwater adhesion ability after storing the adhesive in water/artificial seawater and dry conditions for 30 days.The adhesive strength of the adhesive on the SS substrate can still maintain above 90 k Pa.3.The PAA-PAH coacervate adhesive is fabricated by complexing poly(acrylic acid)(PAA)and poly(allylamine hydrochloride)(PAH)in aqueous solutions.The coacervate adhesive can be used to repair the highly rigid material at the ambient condition based on the known property of reversible intermolecular interactions between PAA and PAH.Firstly,the electrostatic interactions between PAA and PAH can be significantly suppressed via Na Cl due to the charge screening effect.When mixing PAA and PAH aqueous solutions with Na Cl concentrations of 2.5 M,PAA-PAH complexes in a viscoelastic liquid-like state(i.e.,PAA-PAH coacervate adhesives)was formed.Secondly,by exquisitely tuning the electrostatic and H-bonding interactions between PAA and PAH,PAA-PAH composites with in-situ formed phase-separated nanostructures are obtained.The PAA-PAH composites exhibit a tensile strength and an elastic modulus as high as ca.67 MPa and ca.2.0 GPa,respectively.Finally,the high-strength and stiff PAA_1.6-PAH_1.0composite can be simply repaired by using the liquid-like form of PAA-PAH coacervate adhesives as the healing agent.The fractured PAA_1.6-PAH_1.0composite can be effectively healed,the tensile strength and strain at break of the healed sample can be recovered up to 98%and 90%of the values for the pristine sample,respectively.There are two reason for the healing process:(1)The high mobility of the PAA and PAH chains in the hydrated coacervate adhesive enabled them to diffuse across the fractured interfaces.(2)The formation of the reversible electrostatic and H-bonding interactions between PAA and PAH.