| Research Abstract |
a.We could explain the origin of the photochromic enhancement by the additives, including the O-C-H structure, taking account of the electronegativities of oxygen, carbon and hydrogen that have the values rhof 3.4,2.6 and 2.2, respectively, In the O-C bond, the oxygen will more strongly attract the electron than the carbon. Thus, if carbon makes bonds such as O-C-H, the bond strength between the carbon and hydrogen will be much weaker than that between the oxygen and carbon. In such a case, the hydrogen may be easily released with oxidation by the photogenerated hole. On the other hand, if the carbon bonds with an alkyl group, the bond between the carbon and the alkyl group is stronger than that between the carbon and the hydrogen in the O-C-H structure since the alkyl group is an electron donor. It has also been consistently explained that ketones and carboxylic acids do not show the photochromic enhancement because they do not have hydrogen next to the O-C bond.
b.We studied the properties of surface waves during the gelation process of tungstic acid and gelatin and silica gel by the time resolved surface wave measurements. The anomaly is clearly shown in the change of the wave number exponent chi(omega-kappa^2 , the values 1.5 and 1.0 indicate surface tension and elastic wave, respectively). chi of the tungstic acid was about 1.4 in the sol state and rapidly decreased to 1.0 at the gelation point. chi of gelatin was about 1.4 (same as tungstic acid) in the sol state and decreased gradually after the gelation point. On the other side, chi of silica gel remained near 1.5 after the gelation point.
c.We have studied dehydration process of gels, which are improtant to use the sol-gel method, and have found that the feature of the dehydration process has been much affected by the interaction between solvent and polymer network in the gels.
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