Design And Properties Of Self-healing Materials Based On Novel Microcapsules And Metal/Ligand

Polymer materials have been widely used in various fields including aviation and aerospace,electronics,automobile,architecture,sports equipment,etc.due to their excellent properties,such as low density,outstanding mechanical properties,good processing properties,easy functionalization and so on.However,the microcracks or damage will occur when the mateirals are being processed or used,which will lead to macrocracks.These macrocracks will influence the structure integrity and mechanical properties of the materilas,and finally decrease their safety and shorten service life.Biologically inspired by damage-automatical repair mechanism,self-healing polymer materials were developed,which drew much attention becasue these materials can repair themselves after being damaged.Theses materials are classified into microcapsules-based extrinsic self-healing materials and dynamic interactions/supermolecular-based intrinsic self-healing materials.Because microcapsules can be wildely used in various resins and easily designed,the extrinsic self-healing materials developed very fast and the key technology is the preparation of microcapsules.So far,most of the microcapsules for self-healing purpose have been prepared by in situ polymerization and interfacial polymerization.But,both of them usually involve numerous processing steps,complicated temperature control or pH adjustment,a long reaction time and high requirement for the emulsion stability.Besides,these sample microcapsules with one chamber inside can hardly be used in self-healing mateirals to achieve repeatable healing capacity.Fortunately,intrinsic self-healing materials can heal local damage for many times and their structure can be designed as expected to improve mechanical properties or self-healing properties.But there are still some restrictions,such as the weak mechanical properties,limited dynamic interactions in one system,self-healing behavior relying on heat or UV and so on.To solve the problems about the preparation of microcapsules and design new intrinsic self-healing materials,this dissertation mainly focuses on highly efficient reaction for microcapsule preparation and structure design of microcapsules and self-healing polymer.The main contents include the following aspects:???Explore efficient preparation methods for microcapsules?1?Developed an efficient method for healing agent microcapsules by combining click chemistry and Pickering emulsion,simplified processing process and shortened reaction timeTo improve the stability of emulsion droplets,simplify the preparation process and shorten reaction time,the efficient thiol-isocyanate click reaction was combined with Pickering emulsion templet to encapsulate ene component in thiol-ene healing chemistry.Trimethylolpropane tris?3-mercaptopropionate??TMMP?,isophorone diisocyanate?IPDI?and1,3,5-tri-2-propenyl-1,3,5-triazine-2,4,6?1H,3H,5H?-trione?TTT?were mixed and acted as oil phase.The hydrolyzed poly?glycidyl methacrylate?particles?PGMA?acted as stabilizers and were dispersed in water.After shaking the oil/water mixture,triethylamine?TEA?was dropped in above mixture,immediately,TMMP and IPDI were reacted and solidified to a tough polythiourethane shell,producing TTT-loaded microcapsules.The microcapsule formation mechanism was proposed and verified.The morphology,diameter,chemical structure,reactivity of core material,core content of TTT-loaded microcapsules were characterized.Moreover,the influence factors on the diameter and core content were investigated and the self-healing property of TTT-loaded microcapsules was preliminarily discussed.Results show that becase of the orthogonality and high efficiency of thiol click chemistry,thiol selectively reacted with isocyatate in the presense of base catalyst,making ene be encapsulated and the preparation time has been significantly reduced to 10 min.By adjusting the stabilizer concentration and core/shell feeding ratio,TTT-loaded microcapsules with diameter in 110²38?m,shell thickness in 8³6?m and core content up to 67.8%were obtained.What's more,TTT-loaded microcapsules were proved to be qualified for acting as the mate of thiol in making the two-component microencapsulated healing agent of self-healing coating.Moreover,the base catalyzed thiol-isocyanate method was also suitable to encapsulate other enes.The mixture of TMMP,IPDI and TTT also acted as the oil phase of the Pickering emulsion,while the reaction condition was designed as UV initiation.In this way,TMMP selectively reacted with TTT rapidly to form polythioether shell,thus the highly reactive IPDI healing agent was successfully encapsulated.The whole process was completed in 10 min,which significantly reduced the opportunity of side reaction of isocyanate with water.The effect of thiol structures on the morphology of microcapsules was investigated and the microcapsule formation mechanism was proposed and verified.What's more,the morphology,diameter,chemical structure,reactivity of core material,core content of IPDI-loaded microcapsules were characterized and the influence factors on the diameter and core content were studied.Results show that the structures of thiols had a great influence on the shell morphologies of IPDI-loaded microcapsules.The more polar thiols led to porous shell,while the less polar thiols resulted in compact shell which had a good protection for the core materials and endowed the microcapsules with excellent envirment stability.At the same time,IPDI-loaded microcapsules had considerable self-healing property and were proved to be a potential one-component healing agent for anticorrosion coating.?2?Developed an efficient method for curing agent microcapsules by using click chemistry in suspension polymerizationPolyvinyl alcohol?PVA?aqueous solution acted as water phase,UV initiated thiol-ene click reaction was adopted to encapsulate the high polar curing agent,1-benzyl-2-methylimidazole?1B2MZ?.The effects of stabilizer concentration and viscosity of oil phase on microcapsueles were investigated.The curing behavior,kinetics and releasing mechanism of curing agent microcpaules were studied.Moreover,the curing behaviour and self healing ability of epoxy/1B2MZ two-component microcapsules were explored.Results show that thiol-ene reaction could produce 1B2MZ-loaded microcapsules in 20 min.1B2MZ-loaded microcapsules had similar curing ability with 1B2MZ when curing epoxy resin and could make E-51 epoxy resion completely cured at 100 ^oC in 1 h.Epoxy resion with 15%epoxy-loaded microcapsules and 3.5%1B2MZ-loaded microcapsules achieved an average healing efficiency of 66.2%evaluated by tapered doublecantilever beam?TDCB?fracture tests when specimens were healed at 100^oC for 12 h.?3?Developed a new method for novel microcapsules via the aggregation of inverse Pickering emulsion stabilized by polymer particlesPoly?styrene-co-?n-butyl acrylate?-co-acrylic acid??P?St-co-nBA-coAA??particles and Span80 were used to stabilize water in 1-octanol emulsion,which was then heated to aggregrate to form multi-wall hollow microcpasules that could act as a healing agent carrier,which was potential to achieve repeatable self-healing porperties of microcapsules based materials.The formation mechanism of multi-wall hollow microcpasules was revealed by investigating the zeta potential,chemical composition and T_g of P?St-co-nBA-coAA?particles.Becides,the influence of adding amount of Span 80,sintering time and sintering temperature on microcapsules were explained.Results show that the chemical composition was the key factor that decided the formation of novel microcapsules and only proper St/nBA ratio in particles could make emulsion droplets aggregate and thus produce multi-wall microcapsules.When the amount of P?St-co-nBA-coAA?particles was kept the same,increasing the amount of Span 80would decrease the size and hollows number of mcirocapsules.When the sintering temperture was choosen around T_g of P?St-co-nBA-coAA?particles and sinering time was 5 min,multi-wall microcausles with better spherical shape and closed pores would be obtained.???Designed an intrinsic self-healing system by combining hydrogen bonding and dynamic metal-ligand interactions and investigated the systhesis method and influencing factors of the polymer1,3,5-Benzenetrisamides?BTAs?with the capabiliy of forming nanofibers were combined with dynamic zinc-imidazole interactions,developing a novel self healing intrinsic polymer mateiral.Based on the BTA center,reversible addition-fragmentation chain transfer polymerization?RAFT?was chosen to synthesize the star polymer?S-ICP?which was copolymerized by n-butyl acrylate?nBA?and imidazole acrylate monomer?IMZa?.The composition,chemical structure and assembly behavior of S-ICP were studied and the assembly capability,mechanical properties and self-healing properties of S-ICP/Zn²⁺complex were also investigated.Results show that S-ICP with a lower degree of polymerization?DP?would assemble faster and the fiber structures were more clearly observed.All of the three S-ICP/Zn²⁺complexes with different DPs could assemble into short fiber strucutres.However,the ratio of ligand/metal?L/M?had a significant effect on mechanical properties,which could lead to a brittle or elastic material under different L/M ratios.The higher molecular weight of S-ICP could improve the mechanical property and self-healing property.For different DPs of S-ICP under the same L/M ratio,when the DP of single chain achieved 53,the L-M complex could have a good tensile properties.For L-M complex with DP of 71,the tensile properties could compoletely revovered after being healed at room temperature for 2 h.