TEM studies on thin films of natural rubber and polychloroprene crystallized under molecular orientation. II. Highly prestretched thin films

Abstract

Thin films of natural rubber (NR) or polychloroprene (CR) were made by casting a 1.0-2.0 wt% solution in n-hexane or benzene onto the water surface, and were prestretched up to a fairly large amount of strain (500-800%) at an ambient temperature in wintertime. Each of the specimens thus prepared was introduced into a transmission electron microscope (TEM) column with a cryo-transfer specimen-holder and examined by TEM observation without any electron staining. Most of the specimens were isothermally crystallized for 1-2 h inside the TEM column by using the holder before TEM observation: at -25 °C for NR and at -5 °C for CR. On the basis of the morphological observations in bright- and dark-field imaging modes and the selected-area electron diffraction analysis, the identity of the `γ-filaments', which were named by Andrews, and the crystallization mechanism in highly prestretched NR and CR were discussed.