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.

SynopsisHot-stage polarized light microscopy suggests that bulk hydroxypropylcellulose (Hercules Klucel E) is a cholesteric liquid crystal. Rheological measurements indicate this system exhibits shear viscosities similar to those of polyolefin melts except that it has a yield value comparable to suspensions. Birefringent characteristics were observed in shear flow between glass slides. No relaxation of birefringence is observed following flow. Extruded filaments (without applied take-up tensions) show high levels of birefringence and significant orientations from WAXS measurements. These have skin-core structures with highly oriented outer layers which are caused by the flow patterns in the reservoir and die preceding the extrudate. In the case of melt-spun filaments, where tensile elongation occurs, a highly oriented structure of uniform cross section is found. INTRODUCTIONThe history of the development of plastics and fibers from cellulose derivatives dates back more than a ~e n t u r y . l -~ The decline in commercial importance of cellulosics from 1930 coincides with the growth of polymer physical chemistry and structural characterization techniques. Cellulose derivatives have not received the detailed study given to polyolefins, polydienes, etc. Liquid crystalline structure in polymer systems was first observed in concentrated solutions of polypeptides by Courtaulds investigator^^,^ in the mid-1950s. Similar structures were found in solutions of para-linked aromatic p~l y a m i d e s~~ and other relatively rigid aromatic polycondensates.lOJ1 Somewhat surprisingly, liquid crystalline structures were observed in hydroxypropylcellulose-water solutions by Werbowyj and Gray12J3 and othersg shortly thereafter. Liquid crystalline characteristics were reported in a wide range of cellulose derivative solutions by Panar and Will~ox.~* These observations were extended to other cellulose derivatives by Aharoni15 and Bheda, Fellers, and White,16J7 The development of high levels of birefringence and orientation during flow of solutions of hydroxypropylcellulose has been described by Onogi, White, and Fellers18 and Asada et al.19 Similar studies for cellulose acetate butyrate solutions have recently been reported by Bheda et al.17 This report concerns our efforts to study structure development in processing of liquid crystalline cellulose derivatives. The first investigations in this direction were reported by Panar and W i l l~o x~~ in a patent application. More recently, wet spinning of liquid crystalline cellulose acetate butyrate and cellulose tricetate * Permanent address: Institute of Chemical Research, Kyoto University, Uji, Kyoto, Japan.Journal of Applied Polymer Science, Vol. 26,2165-2180 (1981 17 Our interests have been directed toward thermotropic liquid crystalline polymers because solvents may be eliminated, thus avoiding problems of solvent toxicity and recovery and the vagaries of void structures formed during coagulation. The only known thermotropic polymer liquid crystals are aromatic polyesters.lOJ1 I...

Single-walled carbon nanotubes (SWNTs) were well dispersed in both water and organic solvent by the use of fullerodendron as a dispersant. A C60 moiety at the focal point of dendron plays a crucial role in the dispersing process, because dendron having an anthracene unit at the focal point can not disperse SWNTs in THF. The dispersions of SWNTs were characterized by UV–vis–NIR spectroscopy, Raman spectroscopy, SEM, HRTEM, and AFM.

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 walls'side 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.

Morphologies of poly(p-phenylene pyromelliteimide) (PPPI) were investigated by using phase separation during polymerization of pyromellitic dianhydride (PMDA) and p-phenylene diamine (PPDA). Polymerizations were carried out at 330°C for 6 h. PPDA was added to the solution of PMDA in an aromatic solvent at various temperatures after PMDA was entirely dissolved. The morphology of the precipitates was drastically changed with the temperature of PPDA addition (Tad). When Tad was 240°C, the fine particles were formed through the formation of droplets via liquid-liquid phase separation. On the contrary, when Tad was higher than 280°C, the mixture of lozenge-shaped crystals and starlike aggregates of needlelike crystals were formed by the crystallization of oligomers. Tad influenced the degree of imidization of oligomers, resulting in the variation in the morphology of PPPI. Crystal structure and molecular chain orientation of the lozenge-shaped crystals were also investigated by high-resolution transmission electron microscope.