Abstract
Morphology of thin films of natural rubber (NR), which had been crystallized under molecular orientation, was examined by transmission electron microscopy (TEM). Thin films of NR (RSS#1) were made by casting its solution (2.0wt%) in benzene onto the water surface, stretched by a strain of about 200%, and then mounted on carbon-coated grids for TEM. The specimens thus prepared were introduced into a TEM column by using a cryo-transfer specimen-holder and crystallized there isothermally at -25°C. Selected-area electron diffraction of the NR film gave a well oriented h0l-pattern, which illustrated that the chain axis (c-axis) of NR was oriented parallel to the prestretching direction and also the (010) lattice plane was parallel to the film surface: uniplanar axial orientation. The dark-field image of such a film taken using the 200 equatorial reflection showed that narrow bright striations were oriented perpendicular to the prestretching direction and some of them were stacked in that direction to make row structure or shish-kebab-like structure. Each of these striations, namely of “α-filaments” by Andrews, was concluded to be an edge-on lamella which had been grown plausibly in the [100] direction.
