Numerical Simulation Of Micro-Nano Channel Electroosmotic Flow Of PAA Polymer Solution

Microfluidic technology(TAS)has been widely used in biomedicine,environmental monitoring,aerospace,automatic control and other disciplines and fields due to its advantages of miniaturization,easy manipulation,high integration and portability.With the development of microfluidic technology and its wide application in biology,people are more and more interested in electroosmotic flow of viscoelastic fluid at micro and nano scale,Because the fluid involved in the biological field,such as blood,saliva,DNA solution,all show viscoelastic behavior.However,the research on electroosmotic flow of viscoelastic fluid in micro nano system is still in the exploratory stage due to the complex rheological properties of viscoelastic fluid and the complex physical mechanism of micro nano system.In response to this problem,this paper selects the Oldroyd-B viscoelastic constitutive model based on the finite volume method,gives the numerical calculation parameters of the viscoelastic fluid according to the concentration of the PAA polymer solution,and conducts the numerical simulation of the electroosmotic flow of the viscoelastic fluid at the micro and nano scale.The main conclusions are as follows:1)Coupled PNP electrodynamic transport model,the electroosmotic flow of viscoelastic fluid in ion selective system at micron scale was simulated.The effects of applied potential and PAA polymer concentration on the selective surface current,electric field and ion concentration field were analyzed.The results show that the instability of the flow field increases with the increase of applied potential.The polymer solution can restrain the instability of the flow field to a great extent under the influence of viscosity and reduce the maximum average kinetic energy by about 3 times.At the same time,the polymer solution can also make the ion flux of the selective surface more stable,this phenomenon becomes more obvious with the increase of applied potential and polymer concentration.2)Considering the charge regulation characteristics of the the nanochannel wall,the p H charge regulation boundary condition is realized and used in the calculation of the viscoelastic fluid electroosmotic flow of the micro-nano interconnection system to analyze the common influence of p H,the background salt concentration and the polymer concentration.The results show that the surface charge density increases with the increase of solution p H and background salt concentration.Moreover,when the electric double layer overlap,the effect of the surface charge density of the channel wall exceeds that of the applied potential of 0.05 V at p H = 6;The flow of viscoelastic fluid in the nano channel is time-dependent,the velocity in the channel is fluctuant,and the electroosmotic instability occurs in the reservoir.3)Considering the wavy nano channel with surface roughness,the charge regulated boundary condition is also considered,and the effects of applied potential,polymer concentration and surface roughness are explored.The results show that the concentration polarization becomes more and more obvious with the increase of the applied potential.The influence of surface roughness on the electric field in the nano channel increases with the increase of surface roughness,and the fluctuation of fluid velocity in the channel also increases with the increase of surface roughness.Low polymer concentration viscoelastic fluid flow is more sensitive to surface roughness.