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RESEARCH PRODUCT

Polymer translocation through a nanopore induced by adsorption: Monte Carlo simulation of a coarse-grained model

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Dynamic Monte Carlo simulation of a bead-spring model of flexible macromolecules threading through a very narrow pore in a very thin rigid membrane are presented, assuming at the cis side of the membrane a purely repulsive monomer-wall interaction, while the trans side is attractive. Two choices of monomer-wall attraction epsilon are considered, one choice is slightly below and the other slightly above the "mushroom to pancake" adsorption threshold epsilon(c) for an infinitely long chain. Studying chain lengths N=32, 64, 128, and 256 and varying the number of monomers N(trans) (time t=0) that have already passed the pore when the simulation started, over a wide range, we find for epsilonepsilon(c) (nonadsorbing case) that the translocation probability varies proportional to c(trans)=N(trans)(t=0)/N for small c(trans), while for epsilonepsilon(c) a finite number N(trans)(t=0) suffices that the translocation probability is close to unity. In the case epsilonepsilon(c), however, the time it takes for those chains to get through the pore to complete the translocation process scales as tau proportional, variant N(2.23+/-0.04). This result agrees with the suggestion of Chuang, Kantor, and Kardar [Phys. Rev. E 65, 011802 (2001)] that the translocation time is proportional to the Rouse time, that scales under good solvent condition as tau(Rouse) proportional, variant N(2nu+1), with the excluded-volume exponent nu approximately 0.59 in d=3 dimensions. Our results hence disagree with the suggestions that the translocation time should scale as either N(2) or N(3). For epsilonepsilon(c), we find that the translocation time scales as tau proportional, variant N(1.65+/-0.08). We suggest a tentative scaling explanation for this result. Also the distribution of translocation times is obtained and discussed.