mechanism of rectification of polymer motion in an asymmetric nano-channel

Separation is an important process in science and technology. nano-structures are being used widely to improve the resolution and speed of the separation process. for this purpose, the motion of a charged polymer in an asymmetric nano-channel under constant and alternating applied electric fields are studied in this manuscript. computer simulations and theoretical considerations are used to find the optimal condition for the nano-channel as a separation device. it is shown recently that an asymmetric channel acts as an entropic rectifier for polymers in an alternating electric field. here, the mechanism of polymer motion in the channel, composed of consecutive nano-cones, is investigated based on the role of entropic traps. entropic traps are referred to the narrow constrictions before the cones. it is shown that the characteristic time for the polymers to put their monomers in front of narrow constrictions (trapping time) becomes determining, in smaller electric fields. dependence of the polymer velocity in the channel on the strength of the electric field, the cone angle and the time period of the electric field is discussed. finally, the difference between velocities of polymers of various lengths is considered, which is an important parameter for the separation purposes.