چكيده به لاتين
In this research, the effect of soft layer charge density on the behavior of ionic transport in the ion selective nanochannel has been investigated. The phenomenon of ionic selectivity, which is the preference of transfer of counter-ions to the surface charge of the channel wall over co-ions, usually occurs when the nanochannel has an asymmetric geometry. Asymmetric nanochannels usually have very attractive properties including rectification, ionic selectivity, conductivity and ionic concentration polarization. Due to these features, today, many applications of nanochannels inspired by nature, increasing the performance and modifying the behavior of these systems has been considered. Also, the use of soft layer coating on the surface of nanochannels has been considered in order to increase the efficiency of these systems. In the modeling of soft nanochannels, it is usually assumed that the properties of the soft layer and the electrolyte are the same, which is not true for soft layers with high charge density. Also, often in researches, the charge density of the soft layer is considered constant, but in real systems, the charge density of the soft layer is it has spatial distribution functions. For this purpose, in this research, four spatial distribution functions include fixed (type I), exponential (type II), sigmoidal (type III) and soft step (IV) have been considered for the charge density of the soft layer. Also, the investigated nanochannel is a hybrid form, which is a combination of two parts. It is conical and cylindrical. Then, numerical solution of Poisson-Nernst-Planck and Navier-Stokes equations was done using the finite element method under stady-state conditions. The results showed that by changing 𝛼 from 0.2 to 1 at a concentration of 1 mM, the rectification for the exponential function (type II) can increase to 6.129 (ie 5.7 times). On the other hand, at a voltage of 1 V with a change in the charge density in the polyelectrolyte from zero to 100 mol/m3, the selectivity for the fixed (type I), exponential (type II), sigmoidal (type III) and soft step (type IV) distribution functions is 0.9072 , 0.2009, -0.1543 and 0.9031, respectively. According to the results obtained from this simulation, by controlling the charge density of the soft layer, intelligent behavior of nanochannels can be obtained with separation, diagnosis and detection applications.
