| Concrete is a porous and brittle materials.The rebar inside is prone to corrosion in littoral environment because of the permeation of chloridion or any other corrosive ions.This syndrome will reduce the durability of concrete buildings rapidly.Immergence of ion-triggered microcapsule is a efficacious remedy.Once corrosive ions make an incursion,the microcapsule will release inhibitor automatically.Most of the ion-sensitive microcapsules are shelled by polyelectrolytes,which mainly respond to the permeability change under different ionic strength.It’s suited to medicament used as sustained-release capsule,but unsuitable for concrete.In concrete,infiltration inhibitor,antirusting agent or repair agents are normally sticky oily substances.Because of high surface tension,they are difficult to exude though the polyelectrolytic shell after encapsulated,even if the capsule was in a concentrated salt solution.So for concrete application,microcapsules’ shell is better to be disbanded when ionic strength goes over a threshold,not only swollen.However,the polyelectrolytic shell usually is an interpenetrating polyion networks(IPN)formed by interfix and intertwist of polycaution and polyanion under multiple electrostatic attraction.The disaggregation of polycation and polyanion ouly occurs in ultra-concentrated salt solution(>4M).In common cases,charge shield by salt ions just effects IPN’s tightening,loosens or swells the networks.Therefore,the key of microcapsules’ design is to reduce the penetration of polyelectrolytes while keep the shell stable.In this thesis,polyelectrolyte-shelled microcapsules were firstly synthetized by layer-by-layer(Lb L)assembly method.Laponite was used as polyanion and poly(diallyldimethylammonium chloride)modified laponite(PDDA-Laponite)as polycation.It’s believed the Lb L alternation of Laponite and PDDA-Laponite by electrostatic self-assembly is conducive to reduce the critical salt concentration for IPN disaggregation,because the ordered arrangement reduces interlude between polyanions and polycations.O/W Pickering emulsion is a good template for polyelectrolyte Lb L self-assembly.Compared with soluble linear-structured polyelectrolytes,charged solid particles are able to constitute the shell on oily core surface,encapsulated the droplets directly,unlike the traditional Lb L method,by which a solid core template is needed.Polyelectrolytic microcapsules are usually unstable in a waterless environment like dry concrete.In order to make the microcapsule stored in concrete for a long time,methyl hexadecanoate,an impermeable material with solid-liquid phase transition at 28℃ was selected as the solid core substance.The result microcapsules show good compatibility for concrete application.The work secondly was done is the preparation of sodium polystyrene sulfonate-didodecyldimethylammonium/polyacrylamide hydrochloride hydrochloride-laponite(PSS-DDAB/PAH-Laponite)shelled microcapsule by interface assembly of polyelectrolyte complex.This is a one-step process,in which pre-assembly of PSS-DDAB and PAH-Laponite complex decreases interfix of polycation and polyanion,so reduces the intensity of electrostatic interaction.During the interface assembly,the diffusion of PSS-DDAB and PAH-Laponite ion pair causes interface jamming of polyelectrolyte and Laponiten ano-flake,further decreases the interfix,meanwhile the shell structure becomes more stable.interface assembly of polyelectrolyte complex is a simple approach to synthetize polyelectrolytic microcapsules,and the resulting microcapsule shows sensitive response to salt ions and strong viability in alkaline environment of concrete.The assembly mechanism was investigated by comparing interface assembly behavior and sensibility to salt concentration among different polyelectrolyte complex pairs,different ratios of polycation to polyanion,and different shape microcapsules.It’s concluded,interface assembly method is an effective approach to make polyelectrolyte-shelled microcapsule in large scale. |
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