Cao Qianqian, Zuo Chuncheng, Li Lujuan, Yan Guang
College of Mechanical Science and Engineering, Jilin University, Changchun 130022, China.
Biomicrofluidics. 2011 Dec;5(4):44119-4411912. doi: 10.1063/1.3672190. Epub 2011 Dec 21.
We report a molecular dynamics study on non-equilibrium dynamics of polyelectrolyte brushes under external electric fields. In this work, the effects of chain stiffness and salt concentration on static and dynamic responses of the brushes are addressed in detail. Our simulations indicate that varying these parameters induce rich electro-responsive behavior of the brushes. The increase of salt concentration results in the enhancement of an opposite electric field formed by non-equilibrium distribution of cations and anions, which resists stretching or shrinkage of grafted chains. At strong positive electric fields, the flexible brushes are more sensitive to the change of salt concentration. When reversing the electric field, the stiff brushes undergo a conformational transition from collapse to complete stretching. At high salt concentrations, dynamic responsive magnitude of the brush thickness to added electric field is strongly reduced. It was found that the fall time for the stiff brush becomes much shorter than that for the flexible brush. Additionally, increasing ion concentration leads to an excess extension or shrinkage of flexible brushes. For strongly stiff brushes, such phenomenon occurs in the presence or absence of salt.
我们报道了一项关于外部电场作用下聚电解质刷非平衡动力学的分子动力学研究。在这项工作中，详细探讨了链刚度和盐浓度对刷的静态和动态响应的影响。我们的模拟表明，改变这些参数会引发刷丰富的电响应行为。盐浓度的增加导致由阳离子和阴离子的非平衡分布形成的反向电场增强，这会阻碍接枝链的拉伸或收缩。在强正电场下，柔性刷对盐浓度的变化更敏感。当电场反转时，刚性刷会经历从塌陷到完全伸展的构象转变。在高盐浓度下，刷厚度对施加电场的动态响应幅度会大幅降低。结果发现，刚性刷的下降时间比柔性刷的下降时间短得多。此外，离子浓度的增加会导致柔性刷过度伸展或收缩。对于强刚性刷，无论有无盐，都会出现这种现象。
