Transmission electron micrograph images, made at high magnification, of electrospun nanofibers of
polyvinylidene fluoride showed rows of dark dots, separated by about 0.24 nm, along segments of
molecules. The thin fibers supported themselves across tiny holes, so there was no support material in
the field of view. The dots were seen because the electron density of the CF2 groups is three times that of
the intervening CH2 groups. The polymer nanofibers contained crystals with the polymer chains aligned
predominately along the axis of the fiber. A significant degree of long-range translational symmetry,
associated with the planar zigzag of backbone carbon atoms and the average lateral separation of the
molecules, was maintained as the radiation gradually modified the polymer molecules. These high
magnification images showed surprising persistence of the chain-like morphology and segmental motion. Primary radiation damage events were dominant. Many more numerous and damaging secondary
radiation events that are encountered in thicker samples, or in support films were almost completely
avoided, since the only nearby material where secondary radiation could be generated was in the very
thin fiber. The nanofibers contained from 50 to a few hundred molecules in a typical cross section.
Irradiation severed the molecules at slow rates until only two or three molecules remained in the fiber,
and finally the fiber broke. Evidence was noted that irradiation with electrons also caused loss of fluorine
atoms, cross-linking, and chain scission. The entire observed segments of the nanofibers were small
enough for detailed comparison of images with calculated molecular models