FREQUENCY-DOMAIN SPECTROSCOPIC STUDY OF THE EFFECT OF N-PROPANOL ON THE INTERNAL VISCOSITY OF SODIUM DODECYL-SULFATE MICELLES

The rotational diffusion behavior of tetracene in sodium dodecyl sulfate micelles is studied as a function of the n-propanol content of the micellar solution. Fluorescence anisotropy measurements using frequency-domain spectroscopy show that tetracene reorients faster with increasing concentration of n-propanol. This result is consistent with micellar liquid chromatographic studies and lends insight into the role of n-propanol as a mobile-phase modifier. The components of the rotational diffusion tensor are determined from the double-exponential anisotropy decay. These confirm the validity of the Debye-Stokes-Einstein model and allow calculation of the viscosity of the micelle interior. The viscosity decreases from 8 to 4 cP as the concentration of n-propanol increases from 0 to 10% (v/v). The components of the rotational diffusion tensor indicate that the solvation environment of tetracene in the micelle is structurally disordered.