Thermodynamic parameters of Rhodamine B in powder and nanofilms forms

We report the use of UV-Vis absorbance spectroscopy in determining thermodynamic properties of materials based on their absorbance in the visible region of the electromagnetic spectrum. Rhodamine B (RhB) dye which has always been considered to be a non-volatile material, was chosen for the validation of this method because of its well-defined and strong absorbance in this region. Continuous films of RhB suitable for absorbance spectroscopic study were prepared by spin coating in a 0.2 M ethanol solution to determine the sublimation rates and the activation energy of RhB in the temperature range 65-100 A degrees C. For comparison, the same thermodynamic parameters of powder RhB were also determined using thermogravimetric analysis, at higher temperatures (100-180 A degrees C). The sublimation of RhB was determined to be a first-order process by both methods. The activation energies of sublimation calculated by both techniques are in very good agreement. However, the sublimation rates c