两嵌段高分子链在周期管道内扩散的Monte Carlo模拟

Diffusion of diblock copolymer in periodical channels:a Monte Carlo simulation study

高分子链在纳米管道内的静态和动态特性与许多生物技术和生命过程相关.采用Monte Carlo方法模拟研究了两嵌段高分子链(ANABNB)在周期管道内的扩散过程.管道由长度相等的α和β两部分周期排列而成,其中α部分与高分子链A嵌段间存在吸引相互作用,而其他情形均为纯排斥作用.模拟结果表明,高分子链的扩散过程显著依赖于A嵌段长度,且扩散系数随A嵌段长度呈周期变化.通过对链与管道间的吸引作用能图像分析发现,在扩散系数峰位置,A嵌段的投影长度为管道周期长度的整数倍,同时高分子链的扩散规律与均质链在均质管道内的扩散规律一致;在扩散系数谷附近,A嵌段的投影长度为管道周期长度的半整数倍,同时扩散过程存在一系列明显的受限阶段,高分子链在不同的受限位置间跳跃转移.研究结果有助于嵌段高分子链的序列分离和可控输运.

In recent years, the static and the dynamical properties of polymer confined in nano-channels have become a hot topic due to its potential applications in technology, such as genome mapping, DNA controlling and sequencing, DNA separation, etc. From the viewpoint of polymer physics, the properties of polymer confined in nano-channels are affected by many factors, such as the channel size, the channel geometry, the polymer-channel interaction, etc. Consequently,many researches have been extensively performed to uncover the underlying physical mechanisms of the static and the dynamical properties of polymer confined in nano-channels.Although many conformations are forbidden as polymer is confined in channels, the static properties of polymer are found to be still complicated. For the simplest case, i.e., homo-polymer confined in homogeneous solid channels, there are several scaling regimes, in which polymer adopts different conformation modes and the extension of polymer shows different scaling relations with the channel diameter, the polymer length, the persistence length, etc. In addition, the dynamical properties of polymer, such as the diffusivity and the relaxation, have also been extensively studied.Though the properties of polymer confined in homogeneous channels have been well studied, we know little about those of polymer inside compound channels. It is found that the dynamics of polymer in compound channels is quite different from that of polymer in homogeneous channels, and compound channel could be useful for DNA separation and DNA controlled movement.In this work, the diffusion of diblock copolymer（ANABNB） in periodical channels patterned alternately by part αand part β with the same length lp/2 is studied by using Monte Carlo simulation. The interaction between monomer A and channel α is attractive, while all other interactions are purely repulsive. Results show that the diffusion of polymer is remarkably affected by the length of block A（NA）, and the diffusion constant D changes periodically with NA. Near the peaks of D, the projected length of block A along the channel is an even multiple of lp/2, and the diffusion is in consistence with that of homo-polymer in homogenous channels. While near the valleys of D, the projected length of block A is an odd multiple of lp/2, and polymer is in a state with long time trapping and rapid jumping to other trapped regions in the diffusion process. The physical mechanisms are discussed from the view of polymer-channel interaction energy landscape.