Determination of viscosities of alcohols, fatty oils, and mineral oils based on diffusion rates of fluids in a fluorescent microporous conjugated polymer film

초록

A polydiphenylacetylene derivative containing a trimethylsilyl group in one of the two side phenyl rings (PDPA-C1) was examined for use in a film-type solid-state sensor to determine the viscosity of various fluids, such as alcohols, fatty oils, and mineral oils. The fluids readily diffused into the polymer film upon contact and, simultaneously, the fluorescence (FL) emission increased with time to reach a FL enhancing equilibrium. The FL enhancing rate decreased as the viscosity of the fluids increased. The relationship between the time to reach the FL enhancing equilibrium (t(eq), (FL)) and the viscosity of each fluid (eta) was captured well by a modified Forster-Hoffmann equation, log t(eq), (FL) = C + x log eta. The slope (x) values indicate the viscosity sensitivities of the PDPA-C1 film for the fluids, which were determined to be 1.02 for alcohols, 4.15 for fatty oils, and 0.63 for mineral oils. This sensing process yielded not only significantly higher viscosity sensitivities but also higher reproducibility than the conventional sensing process based on the measurement of FL intensity. The typical Forster-Hoffmann equation did not capture the relationship between the probe FL intensity and the fluid viscosity well. The unknown viscosities of commercial oils were identified exactly using the modified Forster-Hoffmann equation as a calibration curve.

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