It was more than 50 years ago that an appearance of birefringence in alginate gels prepared under cation flow was reported for the first time, however, the anisotropic structure of the alginate gel has not been studied in detail. In the present study, anisotropic Ca-alginate gels were prepared within dialysis tubing in a high Ca(2+)-concentration external bath, and optical and small-angle X-ray scattering (SAXS) measurements were performed to characterize the structure of the gel. The observations of the gel with crossed polarizers and with circular polarizers revealed the molecular orientation perpendicular to the direction of Ca(2+) flow. Analyses of the SAXS intensity profiles indicated the formation of rod-like fibrils consisting of a few tens of alginate molecules and that the anisotropy of the gel was caused by the circumferential orientation of the large fibrils. From the observed asymmetric SAXS pattern, it was found that the axis of rotational symmetry of the anisotropic structure was parallel to the direction of Ca(2+) flow. The alignment factor (A(f)) calculated from the SAXS intensity data confirmed that the orientation of the fibrils was perpendicular to the direction of Ca(2+) flow.

Electron spin resonance (ESR) measurements have been performed on metal-insulator-semiconductor (MIS) diode structures of regioregular poly(3-hexylthiophene), RR-P3HT, fabricated on silicon substrates with SiO 2 layers as gate insulators. The conductivity of substrates was chosen so that it does not significantly lower the quality factor of the ESR cavity. Clear ESR signals due to field-induced polarons have been observed at g-values of around 2.002, consistent with those observed in the MIS devices of RR-P3HT fabricated on Al 2 O 3 gate insulators. Carrier spins tend to saturate above the charge concentration of about 0.3%, suggesting the conversion of polarons with spin 1/2 to spinless bipolarons for higher carrier concentrations. The angular dependence of ESR signals exhibits distinct anisotropy, reflecting the fact that the surface of SiO 2 is flatter than that of Al 2 O 3 . These results demonstrate that ESR can be performed on organic field-effect devices fabricated on silicon substrates.

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