Construction Of Silica Particle Clusters And Study On Their Dilatancy Hydrodynamic Properties

In early industrial processing,the occurrence of shear thickening is not conducive to the transportation of fluid in the pipeline and the uniform coating of materials.Later,it was found that when impacted by external forces,the apparent viscosity of shear thickening fluids（STF）increased rapidly and violently.STF even changed from fluid state to quasi solid state.Therefore,shear thickening materials have attracted more and more attention in the field of personal protection.Liquid body armor and other protective equipment can be obtained by combining STF with Kevlar^?,HMWPE^?and other high-performance fibers.Some scholars add additives such as carbon nanotubes and graphene sheets to silica/PEG fluid to prepare multiphase shear thickening materials to adjust the shear thickening behavior.It is expensive and the ductility effect needs to be improved.However,there are no in-depth reports on the influence of particle surface properties on the properties of STF.Based on the properties of particles,a new STF with simple process,remarkable thickening effect and excellent impact resistance needs to be further studied.Inspired by the shear thickening mechanism,silica particles were aminated by silane coupling agent KH550 to explore the effects of KH550 mass fraction,reaction temperature,reaction time and p H value on the modification,so as to obtain the best reaction conditions,increase the amino content on the silica surface,reduce particle agglomeration and improve the dispersion effect;Then the modified particles react with the intermediate polyethylene glycol diglycidyl ether（DGEPEG）to form particle clusters.The particle clusters with different morphological structures are obtained by changing the molecular chain length of DGEPEG and the nitrogen content of silica.The particle cluster model is designed through theoretical analysis.The particle morphology and particle size were measured to find out the best clustered modified particles,which were dispersed in polyethylene glycol to form a shear thickening liquid.Combined with the changes of rheological properties during steady-state shear and oscillatory shear,the influence mechanism and law of the clustering structure of silica particles on the shear thickening of the system were discussed.The experimental results show that the nitrogen content of modified silica is the highest, =up to 0.396%,when the mass fraction of KH550 is 10%,the reaction time is 6 h,the p H of the solution is 9 and the reaction temperature is 90℃.The aggregation of modified silica particles is reduced,the particle size distribution is uniform,and the storage stability in water is twice that of unmodified particles.The particle sizes of six particle clusters Dk1,Dk2,Dk3,Dk4,Dk5 and Dk6formed by the reaction of DGEPEG-400 and DGEPEG-1000 with three kinds of NH₂-Si O₂respectively reach the micron level.Compared with the original Si O₂,the particle sizes of Dk4,Dk5and Dk6 correspondingly reach twice that of Dk1,Dk2 and Dk3,the average particle size of the particle cluster formed by DK5 is the largest,which is 26.03μm.The structures of Dk1 and Dk4are similar,both exist in linear chain structure,which corresponds to the X model;The structures of Dk2 and Dk5 are the most complex,forming a dendritic particle cluster structure with the largest particle size,which corresponds to the Y model;Dk3 and Dk6 have a certain dendritic structure,which corresponds to the Z model.The comparative analysis of three STF fluids successfully prepared:Si O₂/PEG,modified Si O₂/PEG and Si O₂ particle cluster/PEG shows that when the mass fraction of Si O₂ is 35%,the critical shear rate of the fluid is the lowest and the thickening strength is the highest.As the frequency increases from 1.0Hz to 84.8Hz,the storage modulus of unmodified fluid increases from 104.66Pa to 3317.12Pa,an increase of about 32 times,while the storage modulus of modified fluid increases from 88.42Pa to 5418.29Pa,an increase of about 60 times.Compared with other samples,Dk5 with larger molecular weight does not even appear shear thinning.Under the alkaline condition of p H 10,the peak viscosity of Dk5 can increase to952.40Pa·s.G′and G″of Dk5 are significantly higher than those of Si O₂/PEG and modified Si O₂/PEG fluids,almost up to 10~4Pa.Under the action of external force,silica particle clusters gather to form a strong and tough protective layer,while the extended friction catenary shows resistance to shear deformation in the flow process,efficiently transmits and shares the load,and plays an excellent impact resistance.