Kaoru Shimamura

Morphology and structure of highly elastic poly(vinyl alcohol) hydrogel prepared by repeated freezing-and-melting

Morphology and structure of poly(vinyl alcohol) (PVA) hydrogel prepared by the “repeated freezing-and-melting” method have been investigated by X-ray diffraction, scanning electron microscopy, light-optical microscopy, and simple tension test. The PVA aqueous solution gelled highly by using this method to show rubber-like elasticity, reflecting the gel network in which the amorphous chains are physically cross-linked by the crystallites. The gel morphology was characterized by the porous structure, which was originated from the gelation of continuous PVA-rich solution phase segregated around copious ice crystal phases formed upon freezing. The high gelling ability involved in this method was closely related to the segregation mechanism.

Morphology of optically anisotropic agarose hydrogel prepared by directional freezing

Agarose hydrogels which showed optical anisotropy were obtained by the directional freezing of starting isotropic gels under a temperature gradient. The directional freezing caused a crystallization of many isolated ice crystal phases, leaving a honeycomb-like gel phase with a higher polymer content. The crystallographic c-axis of the ice crystals was directed to the temperature gradient. X-ray and optical analyses showed that agarose chains had a strong planar orientation along the wallsside surfaces, which were parallel to the equatorial planes of the ice crystals.Scanning electron microscopy showed that the wall consisted of a large number of sheets stacked along the wall thickness; in each sheet, agarose fibrillar structures were found to be densely aligned. With the application of repeated freezing and thawing, the anisotropy of the segregated gel phases increased.

Morphology of oriented calcium alginate gels obtained by the flow-gelation method

Abstract Cylinder-shaped oriented gels of calcium alginate were prepared by extruding a 2.6 wt% aqueous solution of sodium alginate (guluronate rich) into CaCl 2 solution through a glass tube. Effects of flow rates on chain orientation in solution and in the gel were examined by polarized optical microscopy. During flow, chains underwent planar orientation along the tube wall, which was reflected in the gel state. Increasing the flow rate increased the coil-stretch transition in solution but led to disorientation of chains in the gel due to increasing die swell and longitudinal shrinkage. This effect resulted in the occurrence of the highest anisotropy of the gel at low flow rate. Chain orientation in the gel was characterized by tilting towards the tangential direction with the appearance of a small negative birefringence, which was transformed to a large positive birefringence on drying due to chain realignment in the longitudinal direction. The morphology of the gel was deduced to be sheet-like structures stacked cylindrically with strong intrasheet binding. Scanning electron microscopy and wide-angle X-ray diffraction were both used in the investigation.

Structure change of polyacetylene-Ix− complex by iodine doping

Abstract Specially oriented polyacetylene fibrillar films were prepared by the epitaxial polymerization technique. The fibrils were doped with iodine to various levels, and the structural change was studied using electron microscopy. At low doping levels iodine preferentially takes the form of the I 3 − anion making a periodic lattice within the polyacetylene matrix. Increasing the iodine concentration generates I 5 − anions which disturbe the I 3 − periodicity. Based on these structural results, a transition in the conduction mechanism will be proposed.

Morphology and structure of poly(p-phenylene benzobisthiazole) crystals

The rigid polymer poly(p-phenylene benzobisthiazole) (PBZT) was crystallized from dilute solution. Electron microscopy showed that, on quenching, flat fibrils several nanometers thick were produced. Subsequent heat treatment in a solvent changed the morphology from fibrillar into “segmented ribbon” structure. Isothermal crystallization at a temperature of about 30°C below the dissolution temperature, in general, resulted in aggregation of rod crystals. The polymer chains were oriented normal to the rod crystals. The width of the rod crystal increased with average molecular length, but saturated to a value much smaller than the average molecular length. In the shorter molecular length range, the rod crystals clustered in a fanned-out manner, while with a medium molecular length (ca. 70–120 nm), all rods crystals in a cluster aligned parallel to each other and were of the same length. With longer molecular length (more than ca. 180 nm), the rod growth slowed because of small diffusion constants of molecular chains to the growing face. Based on observation of the morphology and the crystallization process, an isothermal crystallization mechanism is proposed. Because of the rigidity and wide length distribution of polymer chains, the chain ends were inevitably included within the crystals, resulting in crystal defects such as axial shifts, lattice curvatures, and edge dislocations, all of which were observed directly by lattice imaging.

Comparative study of structure and tensile properties of melt-pressed and extruded-blown films of high-density polyethylene

Bulk high-density polyethylene (HDPE) films crystallized from isotropic melts show a spherulite structure; the tensile stress-strain (S-S) curves of such melt-pressed (M-P) films show a characteristic shape caused by necking. On the other hand, extruded-blown (E-B) HDPE films show an anisotropic structure in which lamellae are stacked normal to the extrusion direction. The S-S curves of E-B films showed various shapes for various elongation directions relative to the lamellar orientation direction. When drawn perpendicular to the extrusion direction (parallel to the lamellar orientation direction), the S-S curve showed typical necking behavior resulting from unfolding from one part of the lamellae. When drawn diagonal to the extrusion direction (diagonal to the lamellar orientation direction), the yield stress was smaller due to slippage between the lamellae. When drawn parallel to the extrusion direction (perpendicular to the lamellar orientation direction), the S-S curve was smooth, but it was shown that micronecking occurred repeatedly in various parts of the specimen. The characteristic shape of the S-S curve of the M-P films was reconstructed as the sum of all S-S curves of the E-B films in various directions. From a structural viewpoint, the deformation behavior of the bulk film, which has a spherulite structure, can be simulated at least qualitatively by the deformation behavior of anisotropic E-B films in various directions.

Morphology control of polyacetylenes by epitaxial polymerization

Abstract Acetylene was polymerized on various substrates of the systematic series of homologous isomorphic organic crystals for understanding the mechanism of epitaxial polymerization. Electron microscopy revealed that fibrillar polyacetylenes grew on the substrates and oriented in a zigzag fashion in the specific directions (the [110] and or [010] directions on the (001) substrate surfaces). The number of orientation directions and the orientation distribution of fibrils in cis - and trans - polyacetylenes were characterized for each substrate. The observed growth patterns were mostly explained by geometrical lattice mismatching factors. The exception is the case between trans -polyacetylene and anthracene which is discussed from the view point of interfacial potential energy.

Fractionation and Crystal Morphology of Rigid Polymer, Poly(p‐Phenylene Benzobisthiazole)

Abstract Fractionation of the rigid polymer, poly(p‐phenylene benzobisthiazole) (PBZT), was carried out in dilute solution in concentrated methane sulfuric acid (MSA) using silica gels as packing material of a column. Several combinations of the average chain length of the fractionating materials and the average pore diameter of the gels were examined to improve fractionation resolution. The gels with average pore diameter near the average chain length resulted in high fractionation resolution. Single crystals of the fractionated and unfractionated PBZTs were observed by transmission electron microscopy (TEM). Both single crystals were fundamentally composed of rod crystals with the chain orienting normal to the rods. The unfractionated PBZT made a cluster of parallel rod crystals, where longer chains penetrated a few rod crystals leaving their chain ends within the crystalline core. On the contrary, with the fractionated polymer, extended‐chain rod‐like crystals were dispersed, isolated from each other. This morphology enables us to estimate the chain length visibly by TEM, for which a few milligrams of the material is enough for the observation.

Observation of a solitary rigid molecular chain cilium standing on poly(p-phenylene benzobisthiazole) lamellar crystal

The rigid polymer, poly(p-phenylene benzobisthiazole), crystallized from H2SO4, formed a lamellar crystal in which the polymer chains were oriented perpendicular to the lamellae. It was supposed that the lamellar surface bristled with chain cilia because of wide distribution in the polymer chain length. This region of the bristle would be a transitional structure from full to deficient packing of the polymer chains. Ordinary scanning probe microscopy of the bristled lamellar surface permitted depiction of a layer with a constant population of the cilia. In this work, the method for imaging one single polymer chain end standing on the lamellar surface was developed. From the image it was concluded that an isolated, long cilium did not move extensively at room temperature. In addition, the three-dimensional chain end distribution was determined by several tens of scannings with consecutively varying input energy of the cantilever.

Microstructural study of as-polymerized and isomerized fibrils of trans-polyacetylene

Abstract Two kinds of trans-polyacetylenes (PA) were prepared for electron microscopy. For sample A, cis-PA was isomerized into trans-PA by annealing at 150°C. For sample B, acetylene was polymerized directly to the trans form at 80°C. Electron diffraction showed that the lattice parameters were larger for sample A than those of sample B, especially the b-axis. The expansion resulted from inclusion of remnant cis units as defects in the trans crystal. A lattice image of sample A revealed that crystallites had a fairly broad orientation distribution within the fibril, which was induced by chain extension by the transformation from cis to trans forms. The crystallite dimension along the polymer chain direction was smaller than that in the lateral direction. Based on this structural information, an intrafibrillar hopping mechanism was proposed for the electrical conduction of the iodine doped PA.