The forced translocation of a polymer chain through repulsive nanopores was studied by using Langevin dynamics simulations. The polymer is in the compact globule state at low temperature and in the random coil state at high temperature. Simulation results show that the mean translocation time 〈τ〉 is highly dependent on the temperature T and the minimal 〈τ〉 is located near the coil-globule transition temperature. Moreover, the scaling behaviors 〈τ〉 ∼ N and 〈τ〉 ∼ F are studied, with N the polymer length and F the driving force inside the nanopore. Universal values α = 1.4 and δ = 0.85 are observed for the polymer in the random coil state. While for the polymer in the compact globule state, α decreases from α = 2 at weak driving to 1.2 at strong driving for short N and δ increases with decreasing T in the low F region, but we find universal exponents α = 1.6 for long N and δ = 0.85 in the large F region. Results show that polymer's conformation plays a much more important role than the diffusion coefficient in controlling the translocation time of the polymer chain.
We have investigated the statistical properties of polymer in the environment with low concentration of nanoparticles by using large-scale molecular dynamics simulations. The scaling law for the mean square radius of gyration was examined and simulation results for the polymer lengths 64 ≤ N ≤ 144 yielding a reasonably accurate value of the Flory exponent ν = 0.58 at weak polymer-nanoparticle interaction εPN. Within the same range of N , the mean asphericity of the chain is independent of N . We found that the polymer behaves like a self-avoiding walk chain at small εPN and a compact sphere at large εPN. The results are attributed to the increase in the contact between polymer and nanoparticles with increasing εPN. Normal diffusions of polymer are always observed at whatever εPN and size and concentration of nanoparticles. Our result shows that the normal diffusion behavior of polymer is independent of polymer's state even though there is a phase transition from a desorbed polymer phase at small εPN to an adsorbed polymer phase at large εPN.
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