Research On Slow-Release Properties And Directional Healing Of Microcapsules Modified By Montmorillonite/Fe₃O₄

Cement-based materials are heterogeneous brittle materials that are prone to micro-cracks.The self-healing of micro-cracks is a current research hotspot.Microcapsule technology is a promising method to achieve self-healing of micro-cracks in cement-based materials.Self-healing microcapsules are divided into ordinary self-healing microcapsules and slow release self-healing microcapsules.The core material of the slow release self-healing microcapsules is released from the hole of the wall material to repair the micro-cracks.However,the release rate of slow-release self-healing microcapsules in the current research stage is often too fast.In the preparation stage of microcapsules,the core material flows out too much,the utilization rate is low,and the repair effect of the composite material is greatly affected.At the same time,at present,microcapsules are randomly distributed in self-healing composites,which cannot be distributed in a targeted and concentration gradient like targeted drugs,resulting in a decrease in the self-healing efficiency of composite materials,a waste of microcapsules,an increase in preparation costs,and also an inherent defect of self-healing cement-based materials.In order to explore the slow release characteristics and directional repair of montmorillonite/Fe₃O₄ modified microcapsules,epoxy resin was used as the core material,ethyl cellulose as the wall material,and montmorillonite/Fe₃O₄ as the core modifier.The slow release self-healing microcapsules were prepared by solvent evaporation method.Environmental scanning electron microscope（ESEM）,laser particle size analyzer（LPSA）,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,high performance liquid chromatography（HPLC）and vibrating sample magnetometer（VSM）were used to evaluate the microstructure,particle characteristics,chemical structure,encapsulation efficiency and magnetic response properties of microcapsules.Different amounts of microcapsules were applied to cement-based materials and tung oil-based materials.The self-healing efficiency and self-healing behavior of microcapsules modified cement-based materials were evaluated by strength recovery rate and pore structure.The directional repair performance of microcapsule modified tung oil-based materials was evaluated by corrosion degree.Finally,the slow release mechanism and directional repair mechanism of microcapsules were discussed.The main results are as follows:Ⅰ.Slow release characteristics of microcapsules（1）Montmorillonite modified slow-release self-healing microcapsules were prepared by solvent evaporation method.The microcapsules have good morphology,regular spherical shape and uniform size.The particle size was distributed between 40-160μm.With the increase of montmorillonite content,the particles gradually increased,and the slow release microcapsules had certain agglomeration.With the increase of epoxy resin viscosity and montmorillonite content,the agglomeration between microcapsules showed a weakening trend.（2）The slow release self-healing microcapsules prepared with 9%montmorillonite content of E-44 epoxy resin had the best slow release performance.The cumulative release rates of E-44 and E-51 microcapsules without montmorillonite at 48 h were 44.5%and 59.9%,respectively.The cumulative release rates of self-healing microcapsules prepared with 3%,6%and 9%montmorillonite content of E-44epoxy resin at 48 h were 37.5%,27.3%and 27.1%,respectively.（3）Organic-inorganic hybrid core materials were constructed by using montmorillonite and epoxy resin.Inorganic nano-montmorillonite is composed of a very small number of atomic groups or molecular groups.It has a large specific surface area and strong adsorption performance,which is beneficial to increase its miscibility with epoxy resin,thereby modifying and enhancing the viscosity of epoxy resin.Ⅱ.Directional repair performance of microcapsules（4）Fe₃O₄ modified slow-release self-healing microcapsules were prepared.The microcapsules have good morphology,regular spherical shape and uniform size.The particle size is distributed between 40-160μm.The surface composition of the microcapsules is mainly C and O,accounting for 60.14%and 32.98%of the total mass,and Fe element accounting for 6.88%of the total mass.（5）The saturation magnetization of Fe₃O₄ is 64.3 emu·g^-1,and the saturation magnetization of Fe₃O₄ modified microcapsules is 15.8 emu·g^-1.It has the ability of targeted driving under the action of magnetic field.Ⅲ.Mechanical repair performance of cement-based composite materials（6）Montmorillonite modified slow-release self-healing microcapsules have a certain ability to repair cement-based materials.When the content of montmorillonite was 6%,the self-healing efficiency reached the maximum value of 34.4%.The initial strength of cement-based materials with 3～9%montmorillonite modified slow-release self-healing microcapsules decreased,and the strength decreased by 21.1%,12.5%and6.7%,respectively.（7）Montmorillonite modified slow-release self-healing microcapsules also have a certain repair effect on the pore structure of cement-based materials.The porosity of the cement paste with 6%sustained-release self-healing microcapsules of E-44 epoxy resin is 33.6%after 3 days,the porosity of the cement paste after pre-damage is 38.1%,and the porosity of the cement paste after 7 days is 19.1%.Ⅳ.Directional repair performance of tung oil-based composites（8）Fe₃O₄ modified microcapsules incorporated into tung oil-based materials have directional repair ability.Under the corrosion test,3%,6%,9%wt microcapsules tung oil-based self-healing materials have magnetic response properties.Tung oil-based self-healing coatings can successfully move directly to the damaged area of the metal matrix coating,repair the corroded area,and show excellent corrosion resistance.（9）Fe₃O₄ was used to modify the core material of microcapsules（epoxy resin）.Fe₃O₄ is a regular arrangement crystal,and the molecular current orientation is consistent,which leads to the external magnetic performance.When there is a magnetic field,the magnetic material is subjected to magnetic action,and the internal molecular current of the Fe₃O₄ magnetic material also tends to be regular and is directed.The Fe₃O₄ modified microcapsule core material（epoxy resin）flows directional under the action of magnetic force,thereby filling the cracks in the tung oil-based material.