화학공학소재연구정보센터
Journal of Physical Chemistry, Vol.98, No.8, 2120-2124, 1994
Microviscosity in Water Pool of Aerosol-OT Reversed Micelle Determined with Viscosity-Sensitive Fluorescence Probe, Auramine-O, and Fluorescence Depolarization of Xanthene Dyes
Auramine O (AuO), the fluorescence quantum yield (Phi(f)) of which increases with increasing solvent viscosity, was solubilized in Aerosol-OT (AOT) reversed micellar core (water pool) to determine the microviscosity (eta(W)). This probe is localized at the vicinity of the water/surfactant interface owing to electrostatic association between the polar head groups in AOT and AuO. The microviscosities were determined rapidly as a function of R(W) (=[H2O]/[AOT]) by measuring the Phi(f) of AuO solubilized in the water pool. The AuO fluorescence showed that the water pool is highly viscous in the lower R(W) region; with increasing R(W), eta(W) rapidly decreased below R(W) = 10 and then gradually decreased until the micellar solution became turbid above R(W) = 50. Even in the higher R(W) region, the values of eta(W) were considerably higher than the viscosity of the ordinary bulk water (ca. 1 cP at 25 degrees C). This indicates that the solubilizing water molecules are tightly bound to the polar head groups in AOT. The values of a, as a function of R, obtained by the AuO method coincided satisfactorily with those determined with the fluorescence depolarization of a cationic dye, rhodamine B. Thus, the results led to the conclusion that the AuO probe is useful for rapid determination of the microviscosity in the water pool of AOT reversed micelle. The fluorescence depolarization for different ionic character of xanthene dyes suggested that the water pool is heterogeneous with respect to the microviscosity.