| Viscoelastic materials have attracted much research interest in engineering due to their dual properties of viscosity and elasticity.The change and description of viscoelastic properties are very important for engineering applications of viscoelastic materials.However,current models used to describe viscoelasticity are usually linear combinations of springs and viscous damping bodies.These viscoelasticity models are large workload and low accuracy owing to the massive experimental tests for viscosity coefficient and elastic modulus.The viscosity and elastic modulus will be fixed when the material is determined,therefore,if we can establish the direct relationship between the microscopic parameters and macroscopic physical quantity?viscoelastic properties?from the perspective of molecular origin,then the viscoelasticity can be directly predicted according to the micro nature of materials.Van der Waals'force is one of the most important intermolecular forces and has important influence on the material composition and physical properties,so researching the influence of Van der Waals'force on the viscoelastic will give more explicit explanation of the microscopic mechanism of viscoelastic generated from the micro perspective,and provide guidance for the viscoelastic engineering application and viscoelastic materials development.First,we used the equilibrium molecular simulation to study the influence of the external environmental parameters??*and T*?and explored the mechanism of Van der Waals'force effect on the viscoelasticity of the single atom L-J fluid in the liquid-solid coexistence region of?*=0.8-1.0,T*=0.6-1.5.The results show that the single atom L-J fluid viscosity increased with increasing?*or decreasing T*,infinite frequency shear modulus G?*has positive correlation with?*and T*.The storage modulus G'*and loss modulus G"*in high frequency increase with the increasing?*and T*.Moreover,the higher Van der Waals bond breaking rate decreases viscosity and characteristic relaxation time,the more concentrated particle displacement distribution enhances the material resistance deformation ability in low frequency.Moreover,with the increasing particles potential difference?U*,?loss peak*?G'max*?G”max*,both G'*and G"*increase and tend to high frequency.We found a significant linear relationship between?loss peak*and?U*,and put forward a prediction formula for?loss peak*.Second,we conducted viscoelastic research of single atom L-J fluid in?*=0.9 and T*=0.6with varying potential parameters??=0.8-1.3??=0.97-1.0?.We calculated viscoelasticity??*,G?*,G'*,G"*?and analyzed the mechanism of Van der Waals'force effect on the viscoelasticity with potential parameters.We observed the static viscoelasticity?*and G?*and dynamic viscoelasticity G'*and G"*all increase with increasing?and?,especially for the G'*in the high frequency.In addition,the effect of Van der Waals force on viscoelasticity in different potential parameters can be explained from bond breaking process,dynamic displacement distribution and potential energy difference,the previous?losspeak*prediction formula is still suitable for potential parameters.Finally,we extended the single atom L-J model to mixed atoms L-J system and researched viscoelasticity of mixed systems in?*=0.9-0.95,T*=0.6-0.7,?=0.8-1.3,?=0.98-1.2.We analyzed the viscoelastic variation with temperature,density and L-J potential parameters,discussed Van der Waals force on the influence mechanism of mixed double atomic material viscoelasticity,and further explored the impact of force between dissimilar particles on viscoelasticity.The results show that?*,G?*,G'*and G"*of the mixed systems have similar laws with the single system.We found that the viscoelastic modulus will be different from Maxwell model when potential produced by Van der Waals force appears fluctuations.Additionally,with the increase of heterogeneous interaction between particles,the mixed system will gradually change from insoluble to immiscible.Viscoelasticity is almost unchanged in insoluble state,but once the particles begin mixed,the viscoelasticity will increase significantly with?ab and the system will begin solid gradually. |
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