Polyelectrolyte Self-repairing Microcapsules Were Prepared By Layer-by-layer Self-assembly

As there are coulombian attractions between two polyelectrolytes with heterogeneous charges,core materials could be shelled by these two polyelectrolytes to form a microcapsule by layer by layer?Lb L?alternate self-assembly.This microcapsule is characterized with ionic sensibility,i.e,it could release contents after triggered by various ions.Polyelectrolyte microcapsules have absorbed many attentions in biomedical field because they are used as a carrier in targeted drug delivery or tissue transplantation.In this thesis,polyelectrolyte microcapsules were suggested to be mixed into concrete to resolve the chloride attack and carbonation issure.The incursions of chloridion and carbanion into concrete are the major problems in civil engineering,because they debase durability.The incorporation of Lb L polyelectrolyte microcapsules into concrete could endow the structure with an immune system against harmful ions,enable it to have chemical self-healing capability.The polyelectrolyte microcapsules used in biosome cann't be formed on the surface of core material droplets.Usually,they take shape by Lb L self-assembly first on microball templet,then dissolving the template and inpouring liquid core.The obtained microcapsules must be kept in water.Once the continuous aqueous phase disappeared,the Lb L structure will collapse in disorder.The concrete is an anhydrous matrix.In order to be applicated in civil structures,the Lb L self-self-assembled polyelectrolyte microcapsules must be modified.In our work,three aspects were ameliorated:?1?polyelectrolyte microcapsules formed directly on surface of epoxy droplets;?2?the Lb L structure of shell was fixed by cross-linking between molecular chains of one polyelectrolyte.It stablizes the microcapsule to exist in anhydrous environment like concrete.Besides,microcapsules used in concrete should be fabricated in large-scale and with low-cast,so high efficiency was expected in the preparation of polyelectrolyte microcapsules for self-healing concrete application.In this thesis,polymerizable emulsifier was employed to improve the percentage of microencapsulation.Under irradiation of ultraviolet light,the emulsifier was polymerized on the surface of droplets,to form a negative-charged network layer.In the very beginning,this layer plays an important role to keep the shape and size of droplet in high-speed centrifugation.The LbL self-assembly of polyelectrolytes became more easy on this layer.The experiments include three progressive parts:?1?Preparation of epoxy microcapsule with conventional CaCO₃ templet.In the precipitation reaction of CaCO₃,PSS was added into calcium ion solution to change the sediment morphology from natural cube to round sphere.When the PSS concentration reaches to 5 mg/mL,the CaCO₃ sediment is well-shaped spherical particles.The average grain diameter is 8.6±0.6 ?m,specific surface area 8.8±0.5 m2/g,surface potential about-45 mV.Employing these CaCO₃ sediments as templet,let PAH and PSS self-assemble on its surface alternately to predetermined layers,then dissolving the templet out,a hollow?PSS/PAH?n microcapsule can be obtained.Soaking the hollow microcapsule in alicyclic epoxy T8210,epoxy T8210 will permeate though the wall to fill the microcapsules' core.Infusing the T8210/?PSS/PAH?n microcapsule in glutaraldehyde?GA?solution for cross-linking,the microcapsule will be stable in anhydrous environment like concrete.?2?Liquid core droplet emulsified by ammonium cationic surfactant,then microencapsulated directly by LbL polyelectrolytes.As a demonstration,dodecane was selected as an oily core material,and dimethyldidodecylammonium bromide?DDAB?,a surfactant slightly soluble in water,was used as its emulsifier.The lipophilicity of DDAB's cation is rather better than its hydrophilia,so it will stay in oil phase and spread out on the surface of dodecane droplets,making the emulsion stable.On this positive-charged surface of dodecane droplets,PSS and PAH aggradated alternately in several turns to form dodecane/?PAH/PSS?n microcapsule.then GA solution was employed for cross-linking.?3?Liquid epoxy core droplet stabilized by a mesh negative-charged polymer film,then microencapsulated directly by Lb L polyelectrolytes to form epoxy microcapsule.Epoxy is a good repair agent for concrete.Epoxy E44 mixed with polymerizable surfactant,unsaturated ester epoxy acrylate?UR230D?,acrylamide and methyl hydroxypropyl acrylate sodium sulfonate?HPMAS?.After emulsified,the emulsion was irradiated under ultraviolet light for polymerization.The surfactant will become a mesh-network film on epoxy droplet surface.It's negative-charged,keeps the core stable inside under slight agitation but allows the core outflow under trigger press.On this film,PAH and PSS self assembles by LbL to predetermined layers and then cross-linked,a stable epoxy/polyelectrolyte microcapsule was acquired.The experiments above indicate,GA only reacted with PAH in the two polyelectrolytes.It makes the PAH chain in different layers cross-linked with a pyridine-like structure,endows the shell with a structure of each-series polymer network.This structure stabilizes Lb L make arrangements,allows the microcapsule exist in anhydrous surroundings,but does not affect its response to ions.All the microcapsules synthetized in the experiments above can be triggered and then release content in alkaline solution of which pH value is higher than 12.In this thesis,the preparation method was improved continuously.The progress from microencapsulation of solid spherical template to of liquid epoxy droplet simplifies the preparation process of polyelectrolyte microcapsules,brings more application to it.Cross-linking between PAH by GA stabilizes the polyelectrolyte shell,makes the microcapsule possible to be stored in dry or anhydrous surroundings.After re-soaked in water,microcapsule still responds to ions.By employment of polymerizable surfactant as emulsifier,the Lb L self-assemble of polyelectrolytes of liquid core droplets became more easy.As after the polymerization of surfactant,a stable shell composed of monomolecular layer protect the droplet from breaking or merging.It will increase the microencapsulation efficiency.It's concluded the polyelectrolyte microcapsule made by Lb L self-assemble method can be used in concrete,in which the microcapsule could be triggered by ions automatically,making the concrete self-healed chemically.