Study On Fluid Transport In Boron Nitride Nanochannels

When the size of the material device is reduced to the nanometer scale,some unique materialization phenomena will occur,and the macroscopic laws are no longer applicable.The study of ion transport in nanochannels can improve the nanofluidic theory and achieve a thorough understanding of the physical phenomena in nanofluidics,thus accelerating the development of huge potential innovative applications ’of nanofluidics.In this paper,the molecular dynamics simulation method was used to study the change of ion current in boron nitride nanochannels and the transport characteristics of C60 molecules through nanochannels.The conductivity of nanochannels was determined by four-probe test.The effects of different electrolyte solution concentrations and different wall charge densities on the ion current in the boron nitride channel were investigated by molecular dynamics simulation.It is found that with the increase of electrolyte solution concentration,the ion current increases linearly with the increase of solution concentration at low concentration;at high concentration,the ion current increases slowly,showing a trend of nonlinear growth.The reason is that when the concentration of the electrolyte solution is low,as the concentration of the solution increases,the movable anion and cation also linearly increase.When the electrolyte solution reaches a higher concentration,the thickness of the electric double layer becomes thinner.Excessive counterions will accumulate near the wall,causing a large viscous drag,resulting in a decrease in the electromigration of the solution.The effect of wall charge density on ion current is mainly achieved by the influence of counter ions.First,when the wall charge density is continuously added,in order to maintain the system’s electrical neutrality,more counter ions will be generated,which will promote the ion current.At the same time,the high wall surface charge density also causes the counter ions to accumulate at the near wall surface,causing a large viscous drag,thereby reducing the electromigration rate and reducing the current.Adding C60 molecules to the boron nitride channel revealed that the C60 has different effects on the ion current when it has different charges.Firstly,the volume effect of C60 itself will block the ion transport in the nanochannel,and as the charge of C60 increases,the blocking current will increase.The two influencing factors compete with each other,which leads to the phenomenon of current crossover in the current statistics.Secondly,when analyzing the influence of C60 on the ion distribution through the nanochannel,it is found that the charged C60 will attract the anion to accumulate at the center of the channel,and since the counter ion is highly concentrated at the near wall,this will result in a uniform electrolyte solution.The channel enters,and the cation and cations appear obvious stratification when flowing out from the channel outlet,which provides a new idea and means for the screening and separation of specific ions.Afterwards,a linearly increasing tangential electric field is applied,and it is found that the ion current does not increase linearly with the increase of the electric field strength.By analyzing the distribution of cations around the anion,it is found that too high electric field strength will destroy the interaction of ions and thus the current.A normal increase produces an inhibitory effect.Subsequently,a four-probe test bench was designed and built to study the conductivity of boron nitride nanochannels immersed in sodium chloride solution.When adjusting the concentration of solution at different concentrations,the conductivity of nanochannels showed typical nonlinearity.The change also confirms that at low concentrations,the effect of wall charge on ion current is dominant.At high concentrations,a viscous layer is formed near the wall charge,which reduces the fluidity of the solution and causes the conductivity to continue to change nonlinearly.