Ying-Cai Chen

Simulation study on the translocation of polymer chains through nanopores

The translocation of polymer chains through nanopores is simulated by dynamical Monte Carlo method. The free energy landscape for the translocation of polymer is calculated by scanning method. The dependence of the free energy barrier Fb and the chemical difference Deltamu on the concentration of chains can explain the behavior of polymer translocation at low and high concentration limits. The relationship between Deltamu and the escaping time tau(2) is in good agreement with the theoretical conclusions obtained by Muthukumar [J. Chem. Phys. 111, 10371 (1999)]. Our simulation results show that the relaxation time is mainly dominated by Fb, while the escaping time is mainly dominated by Deltamu.

Effect of attractive polymer-pore interactions on translocation dynamics

The effect of attractive polymer-pore interaction on the translocation of polymer chain through a nanopore under electric field is studied by using dynamical Monte Carlo method. The translocation dynamics is remarkably influenced by the interaction. The translocation time for chain moving through nanopore is strongly dependent on the interaction. It reaches minimum at a moderate interaction which is found to be roughly independent of electric field as well as chain length. At weak interaction region, chain spends long time to overcome the barrier of the pore entrance, i.e., the chain is trapped at the entrance. While at strong interaction region, chain is difficult to leave the nanopore, that is, the chain is trapped at the exit of nanopore. The phenomenon is discussed from the view of free energy landscape.

Escape of polymer chains from an attractive channel under electrical force

The escape of polymer chains from an attractive channel under external electrical field is studied using dynamical Monte Carlo method. Though the escaping process is nonequilibrium in nature, results show that the one-dimensional diffusion theoretical model based on the equilibrium assumption can describe the dependence of the average escaping time (τ(0)) on the polymer-channel interaction (ɛ), the electrical field (E), the chain length (n), and the channel length (L), qualitatively. Results indicate that both ɛ and E play very important roles in the escaping dynamics. For small ɛ, the polymer chain moves out of the channel continuously and quickly. While for large ɛ, the polymer chain is difficult to move out of long channels as it is trapped for a long time (τ(trap)) when the end segment is near the critical point x(C). These results are consistent with the theoretical results for the free energy profiles at small ɛ and large ɛ, respectively. The dependence of x(C) and τ(trap) on ɛ and E are discussed, and specific relations are obtained. The configurational properties of polymer chain are also investigated during the escaping process.

Correlation between shape and size of linear polymer chains

Abstract The correlation between shape (measured by the asphericity parameter A) and size (measured by the square end-to-end distance R2 or the square radius of gyration S2) is investigated using a Monte Carlo technique for linear chains random grown on the three-choice tetrahedral lattice. A positive correlation is found, indicating that a chain conformation of small size is usually more spherical than that of large size. Moreover, the correlation coefficients CA,R2 and CA,S2 are chain length dependent; they decrease with increasing chain length n. The asphericity parameter 〈A〉 is dependent on the bond energy e and can be expressed as 〈A〉=α+β exp (e) for not very short chain (n⩾400). The value α is nearly independent of n while β decreases with n. The result can be explained by the correlation between shape and size.

MONTE CARLO STUDY ON THE ENTROPY OF TAIL-LIKE POLYMER CHAIN WITH ONE END ATTACHED TO FLAT SURFACE

Dynamic Monte Carlo simulations are performed for lattice self-avoiding tail-like polymer chains with one end attached to a non-interacting and impenetrable flat surface. The configurational entropy STL of the tail-like chain is determined by the scanning method. The entropy STL is smaller than that of the free chain without surface SF. The entropy drop ΔS=SF-STL increases linearly with lnn for short chains and increases linearly with n for long chains. However, the average entropy drop per bead ΔS/n decreases with n, indicating that the average effect of the surface on one chain bead decreases with the increase in chain length.

Simulation on the translocation of polymer through compound channels

The translocation of a polymer through compound channels under external electrical field was investigated by Monte Carlo simulation on a three-dimensional simple cubic lattice. The compound channel is composed of two parts: part α with length L(pα) and part β with length L(pβ). The two parts have different polymer-channel interactions: a strong attractive interaction with strength ε(α) for part α and a variable interaction with strength ε(β) for part β. Results show that the translocation process is remarkably affected by both ε(β) and L(pα), and the fastest translocation can be achieved with a proper choice of ε(β) and L(pα). When ε(β) is large, the translocation is dominated by the last escaping process as it is difficult for the polymer chain to leave the channel. Whereas when L(pα) is small and ε(β) ≪ ε(α), the translocation is determined by the initial filling process. For this case, there is a free-energy well at the interface between the part α and the part β, which not only influences the filling dynamics but also affects the translocation probability.

Monte Carlo simulation on the diffusion of polymer in narrow periodical channels

Diffusion of polymer in narrow periodical channels, patterned alternately into part α and part β with the same length lp/2, was studied by using Monte Carlo simulation. The interaction between polymer and channel α is purely repulsive, while that between polymer and channel β is attractive. Results show that the diffusion of polymer is remarkably affected by the periodicity of channel, and the diffusion constant D changes periodically with the polymer length N. At the peaks of D, the projected length of polymer along the channel is an even multiple of lp/2, and the diffusion of polymer in periodical channel is nearly the same as that of polymer in homogeneous channel. While at the valleys of D, the projected length of polymer is an odd multiple of lp/2, and polymer is in a trapped state for a long time and it rapidly jumps to other trapped regions during the diffusion process. The physical mechanisms are discussed from the view of polymer–channel interaction energy landscape.

Simulation on the translocation of homopolymers through sandwich-like compound channels

The forced translocation of homopolymers through αβα sandwich-like compound channels was investigated by Monte Carlo simulation. The interaction between polymer and part α is strongly attractive, whereas that between polymer and part β is purely repulsive. Simulation results show that the translocation is influenced obviously by the length of part β (Lβ) and the starting position of part β (Lα1). For small Lβ, the translocation is mainly governed by the escaping process, and polymer is trapped near the exit of the channel. However, the translocation time can be tuned by varying Lα1 and the fastest translocation can be achieved at relatively large Lα1. Whereas for large Lβ and small Lα1, the translocation is mainly controlled by the filling process. It is difficult for polymer to enter the channel, and polymer is trapped at the first αβ interface. Finally, the dynamics for the filling process and the escaping process are discussed from the view of free-energy landscape, respectively.