Investigation On The Microscopic And Rheological Properties Of The Suspension With Nanoparticles

With the rapid development of nanotechnology in recent years,the Micro-Cold Spray Direct-Write Manufacturing Technology has considerable potential and advantages in the manufacture of micro-nano complex structures due to its low cost,mass production,and high efficiency.In order to obtain high-precision direct writing line width,micro-cold spray direct writing must realize continuous and stable delivery of submicron particles.However,the "mechanical powder feeding,gas powder feeding" method adopted in the existing cold spraying has the problem of agglomeration of powder particles and even blockage of the pipeline.In response to this problem,this paper proposes a new method of "liquid nitrogen to powder,liquid nitrogen to powder".Therefore,it is necessary to fully understand the movement,distribution,suspension and rheological properties of micro-nano solid particles in liquid nitrogen.Molecular dynamics simulation methods is adopted to study the above problems,hoping to provide a theoretical basis for the stable suspension and transportation of micro-nano particles in liquid nitrogen.Firstly,we discuss and analyze the influence of suspension temperature,nanoparticle parameters and solid-liquid interaction on the distribution,movement,agglomeration and suspension stability of the particles in the suspension for the suspension of two nanoparticles.The study found that the microscopic movement of the nanoparticles in the suspension is similar,and the optimal particle size and temperature for the stable suspension of the copper nanoparticles under different conditions in the liquid nitrogen base liquid are obtained.Further research on multi-nanoparticle suspensions is carried out to gain insight into the influence of system temperature,nanoparticle volume fraction,particle size,particle agglomeration degree,and solid-liquid interaction strength on the microstructure,diffusion coefficient and rheological properties of the suspension.The research results show that: compared with pure liquid nitrogen,after adding nano-copper particles,the diffusion coefficient of the system decreases and the viscosity increases;moreover,the more nano-particles added,the more significant the change.In addition,it is found that the diffusion coefficient and viscosity of the suspension are related to temperature,but the relationship is different.Among them,the diffusion coefficient has a linear relationship with the reciprocal of the temperature,and the viscosity has a nonlinear change with the temperature.When the volume fraction is greater than 10%,at the same temperature,the increase of the volume fraction will cause the viscosity of the system to rise sharply.This is mainly affected by the number of agglomerated particles and the state of agglomeration.It is further found that for the same number of agglomerated particles,the smaller the fractal dimension of the agglomerated shape,the greater the viscosity of the suspension.However,the self-diffusion coefficient is not sensitive to particle agglomeration.The particle size and the strength of the solid-liquid interaction have no significant effect on the dynamic properties of the suspension.