Construction And Rheological Performance Study Of Shear-Thickening Materials Based On The Organic-Inorganic Hybrid Systems

In recent years,the process of economic globalization has been accelerating,and human beings’awareness of their own safety and protection has been strengthened,and the development of individual protective materials has become faster and faster.With the continuous development of human civilization,the ancient people used metal,hard ceramics and other protective equipment due to its heavy,inflexible,brittle and hard shortcomings have gradually faded from the stage of the times,the development of light,flexible,high strength flexible protective materials is imperative.Shear thickening fluid is a non-Newtonian fluid,in the absence of any external force or by a small external force will show the form of liquid,when it is applied to a relatively large shear rate or impact,the fluid viscosity will rapidly increase,showing the form of solid,when the external force is released,and will return to the most initial fluid state.Therefore,the shear-thickening fluid and flexible protective materials composite,the construction of new high-performance flexible protective materials,can be both impact resistance,soft and flexible,high wearing comfort characteristics.Based on the organic-inorganic hybridization strategy,the shear-thickening materials of different systems were prepared by using nano-silica（Si O₂）,corn starch（CS）and waxy corn starch（MCS）as the dispersed phases and cross-linked solutions of polyethylene glycol（PEG400）,polyvinyl alcohol（PVA）and boric acid（B）as the dispersing media,specifically:Si O₂/PEG,CS/PEG,MCS/PEG and PVA/B/MCS systems,and then systematically studied the shear thickening effect of the above systems,investigated the influencing factors of the rheological properties and creep properties of these different systems,and elucidated the interaction mechanism of shear thickening materials of different systems.The main research contents are specified as follows.（1）Five kinds of Si O₂ nanoparticles with particle sizes of 20 nm,40 nm,100 nm,400 nm and 600 nm were selected and mixed with PEG400 at different concentrations to prepare dispersions.The results showed that only when Si O₂ with particle sizes of 20 nm and 40 nm were selected and added to PEG400 at concentrations of 15 wt.%and 20 wt.%,respectively,the prepared dispersions.The dispersions under other conditions showed shear-thickening phenomenon,and the shear-thickening range of Si O₂/PEG400 system was narrow and the viscosity change range was small.And further,the interaction between Si O₂ and PEG was analyzed to elucidate the reason of viscosity variation with shear rate for this system.The results show that when the nanoparticle-polymer phase interaction is weak and the particle scale is large,the resistance to interparticle movement is low under shear conditions and the fluid viscosity of the system increases insignificantly.（2）Two different structures of corn starch（CS）and waxy corn starch（MCS）were used as dispersed phases to prepare shear-thickening solutions by mixing with PEG400 at different concentrations,and both CS/PEG dispersion and MCS/PEG dispersion showed obvious shear-thickening phenomena,and the higher the starch content,the higher the initial and maximum viscosity of the dispersions and the smaller the critical shear rate.It shows that when the particles interact with the polymer phase,there is a promotion effect on the shear thickening effect of the system.However,the shear viscosity,stability and solubility of MCS/PEG dispersions are far greater than those of CS/PEG dispersions under the same conditions.This is because there are more amorphous regions in MCS with loose structure and poorly arranged molecules,so the PEG solvent is more likely to enter the amorphous regions inside the MCS molecules,causing the straight-chain starch inside the starch molecules to precipitate out and dissolve in PEG to form a gel,leading to an increase in the viscosity of the dispersion.To verify the effect of interaction and particle morphology on the thickening effect,the dispersions were constructed by selecting the paste-dried MCS and PEG.The results showed that the pasted MCS/PEG dispersions exhibited a significant shear thinning phenomenon.This is because the starch particles in the paste system have been completely dissolved,and the dispersion does not generate"particle clusters"under the action of shear force,and the fluid flow is not subject to any resistance,thus showing the phenomenon of shear thinning.（3）The PVA/B/MCS shear-thickening gel with dynamic double cross-linked network structure was constructed by adding MCS to the PVA/B cross-linked network made of polyvinyl alcohol（PVA）and boric-acid（B）as the dispersion medium,and the viscosity of the PVA/B/MCS system increased with the increase of shear rate,showing the phenomenon of shear-thickening,and the creep performance curve indicated that it had good shape stability and excellent resistance to deformation.This is because the boric acid cross-linked with both PVA molecular chains and MCS,thus forming a three-dimensional network structure,and the addition of MCS made the connection between molecules more tight and complex,and the movement ability of molecular chains was weakened,resulting in a corresponding slowdown of viscosity to shear rate change,thus showing a shear thickening phenomenon,in addition,starch still exists in the PVA/B/MCS system in a part of the granular In addition,starch still exists in the PVA/B/MCS system as a part of the particles,and with the flow of fluid,it will also produce the"particle cluster effect",which will impede the movement of molecules,resulting in an increase in fluid viscosity and a decrease in fluidity,thus forming a shear-thickening colloid.Moreover,the PVA/B/MCS system has good shape stability and impact resistance,which solves the disadvantages of unstable and cold-flowing shear-thickened fluids.