Electrospinning is a modern and versatile method of producing nanofibers from polymer solutions or melts by the action of strong electric fields. The complex, multiscale nature of the process hinders its theoretical understanding, especially at the molecular level. The present article aims to contribute to the fundamental picture of the process by the molecular modeling of its nanoscale analogue and complements the picture by laboratory experiments at macroscale. Special attention is given to how the process is influenced by ions. Molecular dynamics (MD) is employed to model the time evolution of a nanodroplet of aqueous poly(ethylene glycol) (PEG) solution on a solid surface in a strong electric field. Two molecular weights of PEG are used, each in 12 aqueous solutions differing by the weight fraction of the polymer and the concentration of added NaCl. Various structural and dynamic quantities are monitored in production trajectories to characterize important features of the process and the effect of ions on it. Complementary experiments are carried out with macroscopic droplets of compositions similar to those used in MD. The behavior of droplets in a strong electric field is monitored using an oscilloscopic method and high-speed camera recording. Oscilloscopic records of voltage and current are used to determine the characteristic onset times of the instability of the meniscus as the times of the first discharge. The results of simulations indicate that, at the molecular level, the process is primarily driven by polarization forces and the role of ionic charge is only minor. Ions enhance the evaporation of solvent and the transport of polymer into the jet. Experimentally measured instability onset times weakly decrease with increasing ionic concentration in solutions with low polymer content. High-speed photography coupled with oscilloscopic measurement shows that the measured instability onset corresponds to the formation of a sharp tip of the Taylor cone. Molecular-scale and macroscopic views of the process are confronted, and challenges for their reconciliation are presented as a route to a true understanding of electrospinning.

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静电纺丝的分子级图片

静电纺丝是一种通过强电场作用从聚合物溶液或熔体生产纳米纤维的现代通用方法。该过程复杂、多尺度的性质阻碍了其理论理解，尤其是在分子水平上。本文旨在通过其纳米级类似物的分子建模为该过程的基本图景做出贡献，并通过宏观尺度的实验室实验补充该图景。特别注意离子如何影响该过程。分子动力学 (MD) 用于模拟在强电场中固体表面上聚乙二醇 (PEG) 水溶液纳米液滴的时间演变。使用两种分子量的PEG，每个在 12 种水溶液中，不同之处在于聚合物的重量分数和添加的 NaCl 的浓度。在生产轨迹中监测各种结构和动态量，以表征过程的重要特征以及离子对其的影响。使用与 MD 中使用的组合物类似的宏观液滴进行补充实验。使用示波器方法和高速摄像机记录来监测液滴在强电场中的行为。电压和电流的示波器记录用于确定弯液面不稳定的特征开始时间作为第一次放电的时间。模拟结果表明，在分子水平上，该过程主要由极化力驱动，离子电荷的作用很小。离子增强了溶剂的蒸发和聚合物向射流的传输。实验测量的不稳定性开始时间随着低聚合物含量溶液中离子浓度的增加而微弱地减少。高速摄影与示波器测量相结合，表明测量到的不稳定性开始对应于泰勒锥尖尖的形成。面临着该过程的分子尺度和宏观观点，并且提出了对它们协调的挑战，作为真正理解静电纺丝的途径。高速摄影与示波器测量相结合，表明测量到的不稳定性开始对应于泰勒锥尖尖的形成。面临着该过程的分子尺度和宏观观点，并且提出了对它们协调的挑战，作为真正理解静电纺丝的途径。高速摄影与示波器测量相结合，表明测量到的不稳定性开始对应于泰勒锥尖尖的形成。面临着该过程的分子尺度和宏观观点，并且提出了对它们协调的挑战，作为真正理解静电纺丝的途径。