High-resolution electron microscopy of shish-kebab structure in uniaxially oriented polyesters.

点击翻译按钮获取中文摘要

Because the specimen thickness should be smaller than 50nm for direct observation by transmission electron microscopy (TEM), uniaxially oriented thin films of various polyesters were made by applying "shear strain (shear rate= about 4 x 10^6 /sec)" to the respective melts. Electrospinning was also employed for producing nanofibers of the polyesters and of regenerated silk fibroin. There are still several problems to be solved, for example, in the methods for fixing/supporting specimens on the specimen grids for TEM as well as in that the resultant nanofibers are too thick for TEM observation. Although expected high-resolution observation could not be carried out, main results for three years are as follows :1) When poly(butylene terephthalate) (PBT) is crystallized from the melt under a static condition, usual-positive spherulites are formed above 200ーC and unusual ones below 200゜C. For each of the three kinds (usual-positive, usual-negative and unusual types) of 2- dimensional spherul … More ites, which were made by isothermal crystallization from the melt or by solution-cast method, the growth direction of crystalline lamellae in the corresponding spherulite and the origin of its optical property (namely, birefringence) were discussed on the basis of morphological studies.2) Uniaxially oriented thin films were prepared by applying shear strain to the respective melts of poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) PEN and PBT, which are aromatic polyesters. In particular, stacked-lamellar structure was undoubtedly recognized in the films of PEN and PBT, and thus we concluded that shish-kebab structure is formed even in polyesters.3) In order to clarify the structure of melt-spun fibers of poly(p-dioxanone) (PPDX) which is a biodegradable aliphatic polyester, the fibers were investigated by X-ray diffraction and morphlogical observation. PPDX nanofibers were prepared by electrospinning as model specimens for TEM observation. Uniaxially oriented thin films of PPDX and electrospun nanofibers of regenerated silk fibroin were prepared, and morphology of the films and that of the nanofibers were studied.4) Electrospun nanofibers were made for each of aromatic polyesters (PET, PEN, and PBT). The average diameter of PBT nanofibers was about 100nm and the smallest of all the polymers utilized in this project. Average nanofiber-diameters of other all polymers are much greater than 100nm. We found that it is necessary to develop new procedures/methods for making electrospun nanofibers with their average diameters being smaller than 50nm, and then to improve their degrees of chain orientation and of crystallinity. Less