Research Unit Plasma Technology (RUPT), Department of Applied Physics, Faculty of Engineering and Architecture, Ghent University , Sint-Pietersnieuwstraat 41 B4, 9000 Ghent, Belgium.
Department of Organic and Macromolecular Chemistry, Supramolecular Chemistry Group, Faculty of Sciences, Ghent University , Krijgslaan 281 S4, 9000 Ghent, Belgium.
ACS Appl Mater Interfaces. 2017 Sep 27;9(38):33080-33090. doi: 10.1021/acsami.7b08439. Epub 2017 Sep 18.
An atmospheric pressure plasma jet (APPJ) specifically designed for liquid treatment has been used in this work to improve the electrospinnability of a 5 w/v % solution of poly-ε-caprolactone (PCL) in a mixture of chloroform and N,N-dimethylformamide. Untreated PCL solutions were found to result in nonuniform fibers containing a large number of beads, whereas plasma-treated solutions (exposure time of 2-5 min) enabled the generation of beadless, uniform nanofibers with an average diameter of 450 nm. This enhanced electrospinnability was found to be mainly due to the highly increased conductivity of the plasma-modified PCL solutions. Consequently, more stretching of the polymer jet occurred during electrospinning, leading to the generation of bead-free fibers. Plasma treatment also results in an increased viscosity and decreased pH values. To explain these observed changes, optical emission spectroscopy (OES) has been used to examine the excited species present in the APPJ in contact with the PCL solution. This study revealed that the peaks attributed to H, CH, CH, and C species could be responsible for the degradation of solvent molecules and/or PCL structures during the plasma treatment. Size exclusion chromatography and X-ray photoelectron spectroscopy results showed that the molecular weight and the chemical composition of PCL were not significantly affected by the APPJ treatment. Plasma exposure mainly results in the degradation of the solvent molecules instead of modifying the PCL macromolecules, preserving the original polymer as much as possible. A hypothesis for the observed macroscopic changes in viscosity and pH values could be the generation of new chemical species such as HCl and/or HNO. These species are characterized by their high conductivity, low pH values, and strong polarity and could enhance the solvent quality for PCL, leading to the expansion of the polymer coil, which could in turn explain the observed enhanced viscosity after plasma modification.
一种专门设计用于液体处理的大气压等离子射流（APPJ）被用于改善聚己内酯（PCL）在氯仿和 N，N-二甲基甲酰胺混合物中 5 w/v%溶液的可纺性。未经处理的 PCL 溶液会导致含有大量珠粒的不均匀纤维，而经过等离子体处理的溶液（暴露时间为 2-5 分钟）能够生成无珠粒、均匀的纳米纤维，平均直径为 450nm。这种增强的可纺性主要归因于等离子体改性 PCL 溶液的电导率显著提高。因此，在静电纺丝过程中，聚合物射流发生更多拉伸，从而生成无珠粒纤维。等离子体处理还会导致溶液粘度增加和 pH 值降低。为了解释这些观察到的变化，使用了光学发射光谱（OES）来检查与 PCL 溶液接触的 APPJ 中存在的激发态物质。这项研究表明，归因于 H、CH、CH 和 C 物质的峰可能是等离子体处理过程中溶剂分子和/或 PCL 结构降解的原因。尺寸排阻色谱和 X 射线光电子能谱结果表明，PCL 的分子量和化学组成没有受到 APPJ 处理的显著影响。等离子体暴露主要导致溶剂分子的降解，而不是修饰 PCL 大分子，尽可能地保留原始聚合物。可以假设观察到的粘度和 pH 值宏观变化的原因是新化学物质的生成，如 HCl 和/或 HNO。这些物质的特点是电导率高、pH 值低、极性强，它们可以增强 PCL 的溶剂质量，导致聚合物链扩张，这可以解释等离子体改性后观察到的粘度增强。
