Abstract
A spin probe TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy) was dissolved in a tetraethyl orthosilicate sol-gel reaction system and measured by electron spin resonance spectroscopy at 295 K. The nitrogen hyperfine coupling constant was from 1.64–1.66 mT in the sol-gel solutions. The values were sensitive to the ethanol-to-water ratio of the solutions. The hyperfine coupling constant in the xerogels was 1.70 mT, which was almost the same as that in water, indicating that the probe molecules were trapped in silica pores with water adsorbed on the silica surfaces. The motion of TEMPOL in the xerogels was considerably slower than in the sol-gel solutions. The local viscosity estimated was from 70–90 cP. The ESR spectra of TEMPOL were altered during the sol-gel process, indicating that adsorbed water on the silica surfaces has an important role for trapping organic molecules in sol-gel glasses.
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Matsui, K., Kaneko, T., Yaginuma, Y. et al. ESR Study of a Nitroxide Radical in Sol-Gel Glasses. Journal of Sol-Gel Science and Technology 9, 273–277 (1997). https://doi.org/10.1023/A:1018359311661
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DOI: https://doi.org/10.1023/A:1018359311661