Liu Jinglin, Lin David Y, Wei Bin, Martin David C
Department of Materials Science and Engineering, The University of Delaware, Newark, DE, 19716.
Strato, Inc., New York, NY.
Polymer (Guildf). 2017 Jun 2;118:143-149. doi: 10.1016/j.polymer.2017.04.070. Epub 2017 Apr 27.
Electrospinning has become a widely-used method for fabricating polymer nanofibers for various applications including filtration, drug delivery, and tissue engineering. Due to the high extensional forces during the electrospinning process, and the rapid crystallization and solidification during solvent evaporation, molecular orientation may develop within the resulting fibers. The properties of electrospun fibers are expected to be sensitive to level of orientation in the fibers. Various reports have shown an increased modulus with decreased fiber diameter, and molecular orientation has been used to explain this trend. However, there have been relatively few studies of the detailed relationship between fiber diameter and molecular orientation, especially at the single fiber level. Here we report a quantitative study of the orientation in individual electrospun poly(caprolactone) (PCL) and poly(L-lactic acid) (PLLA) fibers using low-dose electron microscopy and diffraction techniques. Our results confirmed that for electrospun fibers of PCL and PLLA processed under similar experimental conditions, the molecular orientation decreased as the fiber diameter increased. The extent of orientation remained high for quite large fiber diameters, with azimuthal orientation of 20 degrees seen up to ~500 nm for PCL and ~2000 nm for PLLA.
静电纺丝已成为一种广泛应用的方法，用于制造聚合物纳米纤维，以用于包括过滤、药物递送和组织工程在内的各种应用。由于静电纺丝过程中的高拉伸力，以及溶剂蒸发过程中的快速结晶和固化，所得纤维内部可能会形成分子取向。预计静电纺丝纤维的性能对纤维中的取向程度敏感。各种报告表明，随着纤维直径减小，模量增加，分子取向已被用来解释这种趋势。然而，关于纤维直径与分子取向之间详细关系的研究相对较少，尤其是在单纤维水平上。在此，我们报告了一项使用低剂量电子显微镜和衍射技术对单个静电纺丝聚己内酯（PCL）和聚（L-乳酸）（PLLA）纤维中的取向进行的定量研究。我们的结果证实，对于在相似实验条件下加工的PCL和PLLA静电纺丝纤维，分子取向随着纤维直径的增加而降低。对于相当大的纤维直径，取向程度仍然很高，PCL在直径约500 nm、PLLA在直径约2000 nm时仍能观察到20度的方位角取向。
