Preparation Of Stimuli-Responsive Nanocontainers And Their Application On Anticorrosion Coatings

The problem of metal corrosion has been one of the most pressing problems in the world.The study of functionalized anticorrosive coating has become a hot research topic in the field of metal corrosion and protection.Chromate conversion coatings are widely used as pretreatment a layer to protect aluminum alloys due to their excellent barrier property and inherent self-healing feature.However,the high toxicity and carcinogenic effects of Cr(VI)substances deviate from the concept of sustainable environmental development.From the current research results,intelligent anti-corrosion coating is most promising to replace the chromate conversion coating.In this paper,we have designed and fabricated pH stimuli-response nanocapsules and introduced them uniformly into the coatings.The results show that the combination of smart nanocapsules and coatings greatly improve the anti-corrosion performance of the coatings,and make the coating have some self-repair function.1.A novel supramolecular switch has been designed to allow multi-stage pH controlled release and reloading.The surface of mesoporous silica microspheres(MSNs)loaded with corrosion inhibitor benzotriazole(BTA)was equipped with the reversible bistable[2]pseudorotaxanes containing 1,6-hexanediammonium(HDA)and 1,6-bis(pyridinium)hexane(BPH)as two recognition sites,as well as cucurbit[6]uril(CB[6])as macrocycles.The assembly process of smart nano-ontainers was characterized by FT-IR,SSNMR,XPS,TG,XRD and N2 adsorption-desorption isotherm.The leakage of BTA at pH 7.0 was negligible.While in the alkaline solution,the nanocontainers released large amounts of BTA.The more alkaline,the faster of releasing rate.When the pH value of the solution was adjusted to acid simultaneously supplemented by heating,the smart nanocapsules stopped releasing the BTA due to the movement of CB[6]blocking the mesopores.CB[6]can be reciprocated on the stalk,the reloading ability of the smart nanocontainers will expand their application areas.2.We demonstrate for the first time how to assemble mechanized hollow zirconia nanospheres(MHZNs),consisting of hollow mesoporous zirconia nanospheres(HMZNs)as nanoscaffolds and supramolecular switches anchored on the exterior surface of HMZNs.The remarkable advantage of substitution of HMZNs for conventional mesoporous silica nanoscaffolds is that HMZNs can suffer the hot alkaline reaction environment,which provides a novel strategy for functionalization and thus achieve dual pH-mediated controlled release functions by simple and practicable assembly procedure.Under neutral solution,cucurbituril[7](CB[7])macrocycles complexed with propanone bis(2-aminoethyl)ketal(PBAEK)to form[2]pseudorotaxanes as supramolecular switches,blocking the pore orifices and preventing the undesirable leakage of cargoes.When solution pH was adjusted to alkaline range,CB[7]macrocycles,acting as caps,disassociated from PBAEK stalks and opened the switches due to the dramatic decrease of ion-dipole interactions.While under acidic conditions,PBAEK stalks were broken on account of the cleavage of ketal groups,resulting in the collapse of supramolecular switches and subsequent release of encapsulated cargoes.MHZNs owning dual pH-mediated controlled release characteristic are expected to apply in many fields.3.Morphologically intact hollow mesoporous zirconia nanospheres(HMZSs)with a hollow core mesoporous shell structure were successfully synthesized by sol-gel protection method and used as scaffolds for smart nanocontainers.L-Carnosine(L-CAR)was proved as green,efficient and mixed-type corrosion inhibitor for protection of carbon steel.Critically,the net charge on L-CAR molecules is influenced by solution pH and matches the changing regularity of zeta potential of HMZSs.Taking advantage of the pH-dependent electrostatic interactions between HMZSs and L-CAR,the smart nanocontainers constructed by directly binding L-CAR to HMZSs conveniently achieve acid/alkaline-responsive controlled release.The smart nanocontainers,L-CAR loaded HMZSs were incorporated into water-borne epoxy coating to assemble the intelligent anticorrosion coatings(IACs).The anticorrosion performances of IACs on carbon steel surface were systematically evaluated by electrochemical impedance spectroscopy(EIS)and scanning vibrating electrode technique(SVET).Compared with pure epoxy coating,IACs demonstrate the more excellent corrosion resistance ability.Through monitoring the corrosion around artificial scratches,it is observed that IACs display the satisfactory self-healing effects,which are attributed to the fact that the smart nanocontainers respond spontaneously to local acidification in micro-anodic zones as well as local alkalization in micro-cathodic zones,rapidly release L-CAR molecules to compensate damaged coatings.4.SiO2-imidazoline nanocomposites(SiO2-IMI)owning high loading capacity of corrosion inhibitor,1-hexadecyl-3-methylimidazolium bromide(HMID)and special acid/alkali dual-stimuli-accelerated release property have been synthesized via a one-step modified Stober method.SiO2-IMI were uniformly distributed into the hydrophobic SiO2 sol to construct "host"-"guest" feedback active coating with superhydrophobic surface(SiO2-IMI@SHSC)on aluminium alloy,AA2024 by dip-coating technique.SiO2-IMI as"guest" components have good compatibility with "host" sol-gel coating,and more importantly,once localized corrosion occurs on surface of AA2024,SiO2-IMI can simultaneously respond to the increase in environmental pH around corrosive micro-cathodic regions and decrease in pH near micro-anodic regions,promptly release HMID to form compact molecular film on damaged surface,inhibiting corrosion spread and executing self-healing function.The scanning vibrating electrode technique(SVET)was applied to illustrate the suppression process of cathodic/anodic corrosion activities.Furthermore,benefiting from superhydrophobic surface,SiO2-IMI@SHSC remained protective ability after immersion in 0.5 M NaCl solution for 35 days,which is far superior to the conventional sol-gel coating with the same coating thickness.The facile fabrication method of of SiO2-IMI/SHSC have great potential to replace non-environmental chromate conversion coatings for practical use.