Short Peptide/Polyoxometalates Underwater Adhesives:Material Design And Adhesion Performance Control

Because the structure and synthesis method of short peptides are relatively simple,the design is flexible,and it is easy to control the composition of amino acids,so we can explore the complex adhesion mechanism of short peptides by exploring the synergism between amino acid residues.In the process of forming short peptide adhesive,the design of short peptide molecular sequence is the key link.The peptide sequences need to meet the following requirements,such as cross-linking site,interfacial bonding group,water-resistant group,curing group,interfacial water removal group and so on in order to meet the effective adhesion under different environmental conditions.Although the interfacial spreading and adhesion ability of short peptide adhesive is relatively good,the cohesion of polypeptide adhesive is relatively poor,which it limits its wide application underwater.It is mainly because the polypeptide chain cannot form a cross-linking network like protein or polymer chain to obtain cohesion.Therefore,it is necessary to develop a new adhesion strategy to achieve the balance of interface adhesion and cohesion.At present,our research group has made some progress and understanding in the construction of short peptides/polyoxometalates underwater adhesives by supramolecular cross-linking polymerization strategy,which it lays a foundation for the following work on improving the interface adhesion and cohesion of short peptides/polyoxometalates.The following two parts of this thesis mainly focus on the interface adhesion and cohesion of short peptides/polyoxometalates:Firstly,According to the fact that natural aquatic attached organisms often achieve effective adhesion in the water environment through the synergistic action of a variety of sticky proteins,we propose a synthesis strategy of underwater adhesive based on the cross-linking assembly of two-component short peptides and polyoxometalates.Using commercial cationic peptides: GHK and SYN-AKE as construction units,negative polyoxometalates as cross-linking units,the underwater adhesive was constructed through the strategy of modular co-assembly.The gelling state and properties of modular co-assembled underwater adhesive of two-component peptides with different molar ratios were investigated.At the same time,the traceable fluorescent underwater adhesive is developed by making full use of the fluorescence characteristics of polyoxometalates.The structural composition and element content of the adhesive were verified by elemental analysis(EA)and thermogravimetric analysis(TGA).It was proved by ESI-MS and FT-IR that the original peptides and polyoxometalates did not change before and after assembly,and the structural integrity was maintained.Scanning electron microscope(SEM)showed that the internal structure of the freeze-dried sample was 3D porous and interconnected with each other.The study of rheological properties shows that the adhesive is a solid-like substance with certain mechanical strength and viscoelasticity,and it shows good stability and self-healing ability with time.The underwater tensile test shows that the adhesive can show good underwater tensile strength by bonding a variety of substrates.The fluorescence properties of the adhesive were proved by fluorescence characterization and other related methods,including fluorescence spectrum,fluorescence lifetime and fluorescence quantum yield.Secondly,natural aquatic attached organisms usually secrete aggregate materials with fluidity to achieve effective interface spreading and adhesion in order to increase the adhesion area.Then,under the influence of the surrounding environment,the aggregates were cured in situ by changing the p H and the covalent or non-covalent cross-linking of the residues.Inspired by this,we use the solvent exchange strategy to optimize the effective interfacial adhesion and bulk cross-linking,depending on the cross-linking strength of short peptide/polyoxometalates adhesives in good and bad solvents.Furthermore,the underwater adhesion performance of short peptide adhesive is greatly improved.We have mainly studied the strategies to improve the underwater adhesion performance in the solvent exchange process in these aspects such as the selection of solvents,the optimization of solvent ratio and the underwater adhesion performance under the optimal solvent ratio.Furthermore,the change of phase behavior of short peptide/polyoxometalates complex was investigated under different volume ratio of ethanol and water mixed solvent.The structural composition and element content of the adhesive were verified by elemental analysis(EA)and thermos gravimetric analysis(TGA).It was proved by ESI-MS and FT-IR that the original peptides and polyoxometalates did not change before and after assembly,and the structural integrity was maintained.Scanning electron microscope(SEM)showed that the internal structure of the freeze-dried sample had a certain cross-linked reticular structure.The underwater tensile test shows that the adhesive formed by solvent exchange strategy can bond to a variety of substrates and has good underwater tensile strength properties.To sum up,In order to solve the contradiction between interface adhesion and cohesion,We propose a synthesis strategy of underwater adhesive based on the crosslinking assembly of two-component short peptides and polyoxometalates.Using commercial cationic peptides: GHK and SYN-AKE as construction units,negative polyoxometalates as cross-linking units,the underwater adhesive was constructed through the strategy of modular co-assembly.In addition,in order to solve the problem of cohesion enhancement in interface adhesion and solidification,we use the solvent exchange strategy to optimize the effective interfacial adhesion and bulk cross-linking,depending on the cross-linking strength of short peptide/polyoxometalates underwater adhesives in good and bad solvents.Furthermore,the underwater adhesion performance of short peptide adhesive is greatly improved.At the same time,it is also proved that solvent exchange can be used to control interface adhesion and curing step by step,which fundamentally solves the cohesion,and greatly improves the underwater adhesion performance of the adhesive.