Microscopic Imaging of Fluorescence Anisotropy of Rhodamine B at the Free and Surfactant-Modified Toluene/Water Interfaces Excited under Total Internal Reflection Conditions

The present study successfully carried out microscopic imaging of the steady-state in-plane fluorescence anisotropy ((r) over bar (in)) of rhodamine B at the free and surfactant-modified toluene/water interfaces excited under total internal reflection conditions with an inverted microscope, a laser system, a linear polarizer, and a CCD camera, which were easy to operate and inexpensive. As surfactants, sodium dodecylsulfate (SDS), Triton X-100 (TX 100), and dihexadecyl hydrogen phosphate (Hdhp) were used. The microscopic Fin images were almost homogeneous regardless of the types and concentrations of surfactants, implying homogeneous interfaces. On the other hand, the peaks of the fluorescence spectrum of interfacial rhodamine B and averaged (r) over bar (in) values depended on the types and concentrations of the surfactants. This (r) over bar (in) dependency was mainly attributable to the change of the rotational dynamics of interfacial rhodamine B by solvation. These results suggested that the proposed method would be a promising one to evaluate the homogeneity of liquid/liquid interfaces and the reactivity of solutes at the interface.