Study on the polymer diffusion in a media with periodically distributed nano-sized fillers.

The effect of nano-sized fillers on the equilibrium and dynamical properties of a linear polymer is studied by using off-lattice Monte Carlo simulation. Fillers are arranged periodically in the system with period d and Lennard-Jones interaction between polymer and fillers is considered. Results show that the statistical dimension and dynamical diffusion of the polymer are dependent on the polymer-filler interaction strength ɛ(pf) and the relative size between R(G0) and d, here R(G0) is the radius of gyration of polymer in dilute solution. Normal diffusion of polymer is always observed in the regime 2R(G0) > d. And the diffusion coefficient D is scaled with chain length N as D ~ N(-α), where the exponent α increases with ɛ(pf). Whereas in the regime 2R(G0) < d ≪ Nl0 with l0 the mean bond length of polymer, normal diffusion is observed only at ɛ(pf) < 2, but the polymer will be adsorbed on the fillers and cannot diffuse at ɛ(pf) > 2. In addition, we find that there is a critical interaction strength ɛ*(pf) = 2 in our model system.

Polymer translocation through a gradient channel.

The translocation of polymer through a channel with a gradient interaction between the polymer and the channel is studied. The interaction is expressed by E = E0 + kx, where E0 is the initial potential energy at the entrance, x is the position of the monomer inside the channel, and k is the energy gradient. The mean first passage time τ is calculated by using Fokker-Planck equation for two cases (1) N > L and (2) N < L under the assumption that the diffusion rate D is a constant, here N is the polymer length and L is the length of channel. Results show that there is a minimum of τ at k = k(c) for both cases, and the value kc is dependent on E0 and driving force f. At large f, the scaling relation τ ∼ N is observed for long polymer chains. But the scaling relation is dependent on the energy gradient k for an unforced driving translocation.