Fumiyoshi Yokoyama

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.

Molecular association complex of urea with polyethylene. Morphology of urea-polyethylene complex and polyethylene crystals obtained from the complex

Abstract We succeeded in preparing the urea-polyethylene complex by the addition of a previously formed urea-paraffin complex in xylene solution of polyethylene at 120°C. This is a substitution reaction in which the guest molecules were changed from paraffin to polyethylene. The reaction mechanism is discussed here. DSC thermal analysis of the urea-polyethylene complex shows that it has a higher melting temperature, 148°C, than either urea and polyethylene. X-ray diffraction measurements show that it has the same hexagonal unit cell dimensions as those of the urea-paraffin complexes. However, scanning electron microscopic observation shows it to have significantly different morphological features from those of the urea-paraffin complexes. The hexagonal prism-like crystal of the urea-polyethylene complex is composed of a number of lamella stacked regularly along the long axis of the crystal. Moreover, it is shown that the polyethylene crystals obtained from the urea-polyethylene complex have morphological ...

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.

Whisker of poly(p-oxybenzoyl-co-p-mercaptobenzoyl)—influence of sequence on polymer morphology

Aromatic polymers are expected to possess outstanding properties. However, in many cases they do not show good processability because of their chain regidity. We have been studying the morphology control of rigid polymers during polymerization to overcome this problem and succeeded in preparing the whiskers of poly (p-oxybenzoyl) and poly (p-mercaptobenzoyl) by the polymerization in liquid paraffin at around 300 °C. These whiskers are formed by the reaction induced crystallization of oligomers during solution polymerization. The preparation of copolymer whiskers is very interesting to design the new materials which are endowed with novel functions. The aim of this study is to prepare the whisker of poly (p-oxybenzoyl-co-p-mercaptobenzoyl) and to clarify the influence of the copolymerization on the morphology, especially focusing on the sequence regularity. The introduction of comonomer unit into polymer chain structure extinguishes the crystal habit due to the lower crystallizability and the whiskers can be obtained by the random copolymerization of 4-acetoxybenzoic acid (ABA) and S-acetyl-4-mercaptobenzoic acid (AMBA) only when κf (the molar ratio of ABA/AMBA in feed) is 1.0–0.7 and 0.05–0. However, the copolymer whiskers are obtained by the polymerization of OS, OOS and SSO monomers which produce the alternating and periodic copolymers. These copolymer whiskers consist of the alternating or periodic copolymer chains and their chains align along the long axis of the whisker. The sequence regularity enhances the crystallizability of cooligomers and this leads to the formation of the whiskers. The sequence regularity in copolymers is a very influential parameter to control the morphology and the copolymer whiskers can be prepared by giving the regular sequences. Copyright

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.

Morphologies of oriented alginate gels crosslinked with various divalent metal ions

Abstract Optically anisotropic cylinder-shaped alginate gels crosslinked with various divalent metal ions such as Ca, Cu, Zn, and Pb were prepared by the flow-gelation method in which semidilute sodium alginate solution was extruded through a tube into metal nitrate salt solutions. Effects of metal ions on the morphological and structural features of the gels were examined mainly by polarized optical microscopy. The chain orientation was characterized by a planar orientation where the mean chain orientation is primarily parallel to the gel surface and normal to the total flow direction, due to diametric expansion and longitudinal shrinkage on gelation. The degree of chain extension and orientation was shown to increase in the order Pb > Cu > Ca > Zn. Scanning electron microscopy of the gels dried rapidly under vacuum showed that all the metal alginate gels had cylindrically developed sheet strucures. Molar ratios of metal ions bound to alginate chains were estimated, using plasma spectroscopy, to be in th...

Molecular association complex of urea with polyethylene: 2. The new preparation methods and morphological study

Abstract New systems for preparing urea-polyethylene complex have been discovered: (a) solid urea-polyethylene solution in xylene with a small amount of aniline; (b) solid urea with seeds-polyethylene solution in xylene. Scanning electron microscopy showed that the complex consisted of lamellae of the order of 1000 A in size. Polyethylene molecules perpendicular to the lamellae exist as extended chains in the hexagonal urea tunnels, much as paraffin molecules in the urea-paraffin complex. Extended chain crystals similar to those crystallized under high pressure were obtained by elimination of the skeletal urea lattices of the complex by methanol. This morphology reflects the conformation of the guest polyethylene molecules.

Control of the Length of Aromatic Polyester Whiskers

The control method of poly(p-oxybenzoyl) (POB) whisker length is reported, with the main focus being on how to make the length of the whiskers longer. The POB whiskers were prepared by the polymerization of p-acetoxybenzoic acid in LPF at 330°C. The increase in whisker length is caused by the way oligomer lamellaepileupalongthelongaxisoftheneedle-likecrystalswithspiralgrowth. From the present detailed morphological observations during polymerization, the tip angle of the whiskers is constant at 80° up to a time 10 min, whereas it becomes significantly sharper to 12° at 30 min. This sharpening of the tip angles seems to be highly related to the degree of supersaturation of the oligomers dissolved in solution. In order to depress the sharpening of the tip angle and to extend the steady-state growth for increase of the whisker length, oligomers were added twice into the polymerization system, after 10 min just before the tip angle becomes sharper and then after 20 min. The addition of oligomers extended the steady-state growth period, and the length was increased from 40 μm to 47 μm with the first addition and then to 50 μm with the second addition. The addition of oligomers during steady-state growth gives the most favourable conditions for continuous growth with spiral growth.

Molecular association complex of urea with polyethylene: 3. Structural studies of the complex

Abstract The crystal structure of urea-polyethylene complex in the hexagonal form, obtained by one of our preparation methods, is analysed by X-ray power diffractometry. In this analysis, the fixed molecular parameters of urea are used, and three models with respect to rotational disorder of the guest polyethylene molecule are assumed. It is shown that the host lattice structure constructed by urea molecules is essentially the same as that of urea-n-paraffin complex. Effects of the disorder structure of the guest on X-ray scattering of the complex are presented. However, there is a difficulty in identifying the disorder structure by X-ray analysis. With the aid of a potential energy calculation between the hexagonal urea tunnel and the guest molecule, a rotational disorder model is preferred.

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.