Study On Synthesis And Properties Of Biomimetic Adhesive Based On Mussels

The adhesive is defined as a sticky substance that can bond two materials together.With the rapid development of economy and science,adhesive materials have been used in many fields such as aerospace,automobile manufacturing,housing construction,wooden furniture,protective films and labels.Due to the low adhesion between commercial adhesives and the surface of the substrate in a humid environment,this shortcoming affects the wide application of adhesives in special fields.Therefore,the development of an adhesive with excellent adhesion in both dry and humid environments is one of the major challenges in interface science and technology.In nature,biological mussels have excellent adhesion capacity,fast curing speed and super waterproof adhesion,its characteristics are not available in any kind of synthesized adhesives.Therefore,the preparation of mussel-inspired adhesives is one of the very effective ways to solve the above challenges.Although there are many studies on mussel-inspired adhesives,the research content mainly focuses on the adhesion ability of mussel-inspired adhesives.There is no more expansion of the functionality of the mussel-inspired adhesive.Therefore,this paper prepared a mussel-inspired adhesive with more functionality,such as degradability and wearable tensile strain sensing.A free-radical copolymerization method was used to prepare a mussel-inspired adhesive that has excellent adhesion in both dry and humid environments.First,a polymerizable monomer methacrylic anhydride-dopa(L-DMA)containing both catechol(DOPA)structural units and vinyl groups was designed and prepared,and then L-DMA and butyl acrylate(BA)were reacted to obtain a kind of mussel-inspired adhesive(P(BA-co-L-DMA)).The structure of the synthesized P(BA-co-L-DMA)was characterized by fourier transform infrared spectrometer(FTIR)and nuclear magnetic resonance(NMR),and the content of L-DMA in the adhesive was calculated by ultraviolet spectroscopy.The curing conditions,molecular weight,and mechanical strength of the P(BA-co-L-DMA)were discussed.And we focused on evaluating its bonding ability in air and water.Since the catechol in the DOPA structure has the effect of oxygen inhibition,so we adopt the method of"freeze-pump-thaw"to avoid the oxygen inhibition.When added L-DMA,the bonding performance of the P(BA-co-L-DMA)is significantly improved.When the Mw of the adhesive is 86700,the maximum bonding strength is 2.22 MPa on the steel,when the Mw is 78000,the maximum bonding strength is 1.77 MPa on the aluminum,when Mw is 46000,the maximum bond strength on PP and PTFE is 0.58 MPa and 0.14MPa,respectively.In addition,adding IO₄^-or Mn³⁺ions to the adhesive can significantly improve the bonding strength of adhesive to the steel in humid environments,the maximum bonding strength can reach 1.11 MPa.Its underwater bonding strength is more than 10 times that of commercialized Araldite fast curing epoxy glue.Because the free radical thermal polymerization process is too slow and P(BA-co-L-DMA)cannot be degraded,due to the UV polymerization technology has the characteristics of fast reaction speed and low energy consumption,so we use UV polymerization technology to combine L-DMA and polycaprolactone(GPCL-MA)to prepare a kind of UV curable mussel-inspired adhesive(L-DMA-GPCL-MA).The structure of L-DMA-GPCL-MA was characterized and analyzed by FTIR,NMR and gel permeation chromatography(GPC).At the same time,the UV polymerization kinetics and crosslinking density of the L-DMA-GPCL-MA adhesive were studied.The influence of catechol groups on the mechanical strength and bonding strength of the adhesive was also studied.The UV polymerization technology greatly shortens the polymerization time of the L-DMA-GPCL-MA.40 s of UV radiation is sufficient to achieve the maximum degree of polymerization.In addition,the introduction of L-DMA will reduce the toughness and thermal stability of the adhesive,but it will improve the bonding ability of the adhesive.The bonding strength of L-DMA-GPCL-MA on the steel,aluminum,glass,pigs skin,PP and PTFE substrates is 1.50 times,1.49 times,1.61 times,1.72 times,2.84 times and 3.41 times higher than that of the pure GPCL-MA adhesive,respectively.Because the mechanical properties of the L-DMA-GPCL-MA adhesive are not adjustable and the functionality is less,we continue to use UV polymerization technology to combine L-DMA with functional polycaprolactone(xPCL-MA,x=Di,G,M)to prepare a kind of mussel-inspired conductive hydrogel adhesive(L-DMA-xPCL-MA)with adjustable mechanical properties.The structure,swelling rate and gel of the prepared hydrogel adhesive were studied.The UV polymerization kinetics,microscopic morphology,mechanical properties and bonding properties were also characterized and discussed.At the same time,its electrical conductivity and piezoelectric sensitivity were also explored.Like the L-DMA-GPCL-MA adhesive,the L-DMA-xPCL-MA hydrogel adhesive could reach more than 93.9%conversion by using UV polymerization technology with only 720 s of UV radiation.Adjusting the type of x in xPCL-MA can achieve the adjustment of the mechanical properties of the hydrogel adhesive.The adjustable range of its mechanical properties is:tensile stress:50.2-76.4 k Pa,tensile strain:700-1140%,Young's modulus:8.6-14.8 k Pa,fracture energy:16.4-25.9 k J/m³.At the same time,the L-DMA-xPCL-MA hydrogel adhesive exhibits excellent adhesion performance and repeatable adhesion,After 8consecutive adhesion/peel cycles,the adhesion strength remains almost unchanged.And when it was used as an electronic strain sensor,it exhibits high sensitivity and rapid monitoring accuracy in human motion monitoring.