Electrophoresis of a Bead-rod Chain through a Narrow Slit: A Brownian Dynamics Study

~Received 28 May 2004; accepted 16 August 2004!We use two-dimensional Brownian dynamics simulations to study the electrophoresis of a bead-rodchain through a narrow slit. A constant electric field is assumed to act inside and outside of the slit,and each bead on the chain is assigned a constant uniform charge. We calculate the dependence ofthe polymer transit velocity on chain length, slit dimensions ~width-to-length ratio!, andelectric-field strength. For sufficiently narrow slits, the transit velocity increases nonlinearly with theapplied field for low-field strengths, whereas it increases linearly for high-field strengths. In thelow-field strength region and for sufficiently narrow slits, the transit velocity decreases rapidly forsmall chain lengths and then decreases slowly beyond a critical chain length. As the slit widthincreases, the transit velocity decreases with chain length in more continuous manner, and forsufficiently large slits the transit velocity becomes independent of chain length as expected.Distributions of the chain end-to-end distances and the translocation times depend strongly on therelative size of the chain to the slit. These results show the sensitivity of the transit velocity vs chainlength relationship to the slit dimensions and applied electric-field strength, and suggest that theremay be an optimal slit width for a given field strength and vice versa. The results may be useful formicrofluidic separations and for understanding the motion of biological polymers through narrowconstrictions. © 2004 American Institute of Physics. @DOI: 10.1063/1.1804492#