Kongkhlang Thontree, Tashiro Kohji, Kotaki Masaya, Chirachanchai Suwabun
The Petroleum and Petrochemical College, Chulalongkorn University, Chula Soi 12, Phyathai Road, Pathumwan, Bangkok, Thailand 10330.
J Am Chem Soc. 2008 Nov 19;130(46):15460-6. doi: 10.1021/ja804185s. Epub 2008 Oct 25.
Electrospinning is widely accepted as a simple and versatile technique for producing nanofibers. The present work, however, introduces a new concept of the electrospinning method for controlling the crystal morphology and molecular orientation of the nanofibers through an illustration of a case study of polyoxymethylene (POM) nanofibers. Isotropic and anisotropic electrospun POM nanofibers are successfully prepared by using a stationary collector and a rotating disk collector. By controlling the voltage and the take-up velocity of the disk rotator, the morphology changes between an extended chain crystal (ECC) and a folded chain crystal (FCC) as clarified by a detailed analysis of the X-ray diffraction and polarized infrared spectra of the POM nanofibers. Herman's orientation function and dichroic ratio lead us to a schematic conclusion--that (i) molecular orientation is parallel to the fiber axis in both isotropic and anisotropic POM nanofibers, (ii) a single nanofiber consists of a nanofibril assembly with a size of 60-70 A and tilting at a certain degree, and (iii) the higher the take-up velocity, the smaller the nanofibril under the (9/5) helical structure of the POM chains. It should be emphasized here that the electrospinning method is no longer a single nanofiber producer but that it can be applied as a new instrument to control the morphology and chain orientation characteristics of polymer materials, opening a new research field in polymer science where we can understand the relationship between structure at the molecular level and the properties and performance at the macroscopic level.
静电纺丝作为一种生产纳米纤维的简单且通用的技术已被广泛接受。然而，本工作通过聚甲醛（POM）纳米纤维的案例研究，引入了一种静电纺丝方法的新概念，用于控制纳米纤维的晶体形态和分子取向。使用固定收集器和旋转盘收集器成功制备了各向同性和各向异性的静电纺POM纳米纤维。通过控制盘式旋转器的电压和收线速度，POM纳米纤维的X射线衍射和偏振红外光谱的详细分析表明，其形态在伸直链晶体（ECC）和折叠链晶体（FCC）之间发生变化。赫尔曼取向函数和二向色比使我们得出一个示意性结论：（i）在各向同性和各向异性POM纳米纤维中，分子取向均与纤维轴平行；（ii）单根纳米纤维由尺寸为60 - 70 Å且有一定倾斜度的纳米原纤组件组成；（iii）收线速度越高，在POM链的（9/5）螺旋结构下纳米原纤越小。在此应强调的是，静电纺丝方法不再仅仅是一种单一的纳米纤维生产方法，而是可以作为一种控制聚合物材料形态和链取向特征的新工具，为聚合物科学开辟了一个新的研究领域，在这个领域我们可以理解分子水平的结构与宏观水平的性能和表现之间的关系。
