Electrophoretic stretching of tethered polymer chains by travelling-wave electric fields: tunable stretching, expedited coil-stretch transition, and a new paradigm of dynamic molecular probing
Electrophoretic stretching of tethered polymer chains by travelling-wave electric fields: tunable stretching, expedited coil-stretch transition, and a new paradigm of dynamic molecular probing
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DOI：
10.1039/c1sm06485a
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发表时间：
2012-01-01
期刊：
影响因子：
3.4
通讯作者：
Wei, Hsien-Hung
中科院分区：
文献类型：
--
作者：
Li, Yen-Ching;Wen, Ten-Chin;Wei, Hsien-Hung
从理论上研究了低频行波场在带电聚合物链电泳拉伸中的应用。我们发现，使用简单的弹性哑铃模型，有或没有波动的拉伸行为可以表现出许多在通常的稳定或交流电场中看不到的独特特征。在没有波动的确定性研究中，我们表明，末端束缚的带电聚合物链可以被行波场产生的不对称行程拉动，并沿着波保持延伸。研究发现，虽然平均链延伸可以通过提高场强来增加，但可以通过增加波速来降低。这是在零均值时间周期场中实现聚合物链拉伸的新例子。由于这里的自由能景观就像一个具有双井或多井的振动谐振子，行波场产生的能量槽中的一条拉伸链可能会由于波动而跳回到较低的能量线圈状态。在这项随机研究中，我们发展了一种理论并进行了布朗动力学模拟，结果表明，只要波速不超过阻尼阈值，并且波动不会导致拉伸减小，增加波速就可以通过防止链条跳跃到线圈状态来帮助链条保持拉伸。此外，两种不同的跳跃动力学，阿伦尼乌斯模式和克莱默模式，可以存在来控制双井和多井场景中各自的线圈拉伸转变，具体取决于拉伸程度。这些特征是行波场和涨落协同作用的结果，并进一步通过舌状线圈拉伸相图表现出来。还通过在纳米级或单分子水平上监测和调节循环拉伸聚合物链上的分子传输来说明本拉伸在动态分子探测中的应用。
The use of low-frequency travelling wave fields in electrophoretic stretching of charged polymer chains is investigated theoretically. We find, using a simple elastic dumbbell model, that the stretching behavior with and without fluctuations can show a number of distinctive features that cannot be seen in usual steady or alternating current electric fields. In the deterministic study without fluctuations, we show that an end-tethered charged polymer chain can be pulled by asymmetric strokes generated by a travelling wave field and kept extended along the wave. It is found that while the averaged chain extension can be increased by raising the field strength, it can be decreased by increasing the wave speed. This is a new example that stretching a polymer chain can be realized in a time periodic field with zero mean. As the free energy landscape here acts like a vibrating harmonic oscillator having double or multiple wells, a stretched chain trapped in an energy groove created by a travelling wave field can hop back to the lower energy coil state due to fluctuations. In this stochastic study, we develop a theory and carry out Brownian dynamics simulations to show that as long as the wave speed does not exceed the damping threshold and fluctuations do not prevail to diminish stretching, increasing the wave speed can help the chain maintain its stretch by preventing it from hopping to the coil state. In addition, two distinct hopping kinetics, Arrhenius and Kramers modes, can exist to govern the respective coil-stretch transitions in the double-well and multiple-well scenarios, depending on the extent of stretching. These features are the results of cooperative effects of travelling wave fields and fluctuations, and further manifested by tongue-like coil-stretch phase diagrams. Applications of the present stretching to dynamic molecular probing are also illustrated by monitoring and regulating the molecular transport over a cyclically stretching polymer chain at the nanoscale or single-molecule level.