Masayoshi Ohara

Direct imaging of molecular chains in a poly(p-xylylene) single crystal

Abstract Individual chains comprising a β-form poly( p -xylylene) (PPX) single crystal were resolved with a high resolution electron microscope (JEM-500). In a polymer crystal the important limiting factor for resolution is radiation damage. The total end point dose of a PPX crystal is about 0.5 coulomb cm −2 for 500 kV electron irradiation which is more than 20 times greater than that for a polyethylene crystal. The high resolution image obtained was processed by optical filtering to reduce noise due to the granularity of film. The processed image, which corresponds to the ab -plane projection of polymer chains, shows clearly the mutual arrangement of each molecule in the crystal. This high resolution image is sufficient to provide a starting point for determining the unknown crystal structure of the β-modification of PPX.

Structural analysis of β-form poly(p-xylyene) starting from a high-resolution image

Abstract The crystal structure of β-form poly( p -xylylene) is analysed starting from a high-resolution image of a single crystal of this polymer. The high-resolution image corresponding to the projection of molecules onto the ab -plane along the chain axis shows clearly the mutual position of each molecule in a unit cell. The molecules are aligned wavily in the direction along the a -axis and the rough positions of their centres in a unit cell can be determined from the image. The refinement of the structure is carried out by the usual least-squares method using the intensities of electron and X-ray diffractions. The space group of the β-form is trigonal, P3, and the lattice dimensions are a =2.052 nm, c =0.655 nm and γ =120°. The unit cell contains 16 molecules and one of them is considered to occupy statistically one of three equivalent orientations so as to satisfy the P3 symmetry.

Setting angle of molecular chains in polyethylene crystals

Abstract The setting angles of chains in solution-grown crystals of paraffins were measured from optical transforms of their electron diffraction patterns. Those of solution-grown, melt-crystallized, and drawn polyethylenes were determined by the x-ray diffraction method. The cell dimensions, paracrystalline disorder, and thickness and size of crystallites of these specimens were measured. From these data, factors increasing the setting angle were found as follows; (1) folding of molecular chains, (2) imperfections of crystal lattice, (3) expansion of cell dimensions and (4) smallness of thickness and lateral size of crystallites. The temperature dependence of the setting angle is also discussed; the higher the temperature, the larger the setting angle. At low temperatures, the setting angle also increases, and the values are compared with those predicted theoretically from the minimization of lattice energy. The temperature dependence of the setting angle is interpreted in terms of a conformational chang...

Substrate-induced crystallization of n-paraffins on oriented polyolefins

n-Paraffins of n-C20H42 to n-C50 H102 were epitaxially crystallized on oriented polyolefins; polyethylene, polypropylene, poly-1-butene and poly-4-methyl-1-pentene. In most cases, n-paraffin crystals were epitaxially grown on the substrate surface with the (001) basal plane parallel to it, maintaining a two-dimensional lattice coincidence with the polymer substrate. The epitaxial modes with this orientation were classified into the following three types irrespective of the polymers: 1. (1) (001)p‖SS, 〈110〉p‖FA, 2. (2) (001)p‖SS, [010]p‖FA, 3. (3) (001)p‖SS, 〈110〉 p

MORPHOLOGIES OF MELT-CRYSTALLIZED THIN FILMS OF NYLON-6, NYLON-6,6, AND THEIR BLENDS AS REVEALED BY TRANSMISSION ELECTRON MICROSCOPY

gaFA , where p, SS and FA denote n-paraffin crystals, substrate surface and fiber axis of the polymers, respectively. The angle α depends on the kind of polymer substrate. n-Paraffins longer than n-C40H82 were laid down in parallel on the polypropylene substrate with their axes at a 46° angle with respect to the substrate fiber axis.

Direct imaging of the molecular arrangement in a radiation-sensitive polymer single crystal: poly (tetramethyl-p-silphenylene siloxane)

Permanganic etching was performed on high-speed spun (HSS) and regular fibers of poly(ethylene terephthalate) (PET), and their surface morphologies were investigated via the two-stage carbon replica method using a transmission electron microscope (TEM). The HSS PET fibers, with disordered amorphous regions, showed peculiar surface morphology; many small warts corresponding to the pits of etched disordered amorphous regions were observed. Such unevenness, however, was hardly observed on the surface of the permanganic-etched regular PET fibers, with well-oriented amorphous regions, or on the surface of alkali-etched HSS PET fibers. The permanganic etchant removed the disordered amorphous regions more preferentially compared with the alkali etchant.

Direct observation of dislocations in polymer single crystals

Thin films of nylon-6 (N6), nylon-6,6 (N66), and their blends (N6/N66 = 70/30, 50/50, and 30/70) were prepared by casting from solution (1.0 wt%) in formic acid under ambient conditions. The dried films were melted at 260°C or 280°C and then isothermally crystallized at 200°C. Morphological observations and selected-area electron diffraction (SAED) by transmission electron microscopy (TEM) of the resulting films revealed the following results: All specimen films (N6/N66 = 100/0, 70/30, 50/50, 30/70, and 0/100) had fibrillar entities that were undoubtedly crystalline judging from SAED and dark-field (DF) imaging. Some of the fibrillar entities were constituents of a spherulite or a sheaflike structure (namely, an immature spherulite). To delete the “memory” of the structures of the N66 component that were formed in as-cast films, the films have to be melted at 280°C. As to isothermal crystallization of the blends at 200°C after melting at 280°C, it is postulated that the N66 component first starts to crystallize, and then the N6 one starts to crystallize afterward.

Epitaxial growth of isotactic polypropylene on oriented polyethylene from solution

Abstract A high-resolution electron micrograph of a radiation-sensitive polymer, a poly(tetramethyl-p-silphenylene siloxane) single crystal, was taken with a minimum-dose system. A resolution of 0·32 nm was attained in the image as judged from the optical diffraction pattern of the original negative. To enhance the image quality, the original micrograph was processed by optical filtering. In the processed image, individual molecules could be distinguished and their arrangement in the crystal was found to be in good agreement with an X-ray diffraction analysis of the structure.