Nonexponential dielectric relaxation dynamics in supercooled liquid and glassy states of isoamyl bromide and 2-methylpentane mixtures

摘要

The dielectric spectra of mixtures of the polar solute isoamyl bromide in 2-methylpentane have been ~stigated in the frequency range 1 mHz to 1 MHz and in the temperature range approaching the is transition temperature. The results obtained from the spectra are compared with those obtained :ntly [I. Chem. Phys. Ill, 10979 (1999)] on pure isoamyl bromide. It is found that on increasing .tion with the nonpolar solvent, the width of the curves of the dielectric spectra increase lificantly, and this is reflected in the increase in the nonexponential nature of the relaxation amics. This is found to be a consequence of the decrease in the cooperativity of the relaxation amics and or an increase in the heterogeneity of the solution. The data are found to fit the riliak-Negami equation extremely well. The data at low and high frequencies also fits the liversallaw," since the latter is a low and high frequencies limiting case of the Havriliak- ;ami equation. The scaling parameters of this law are calculated for the 25 mol % solution of myl bromide in 2-methylpentane, and these are shown to experimentally relate to the H-N Lffieters. The stretched exponential parameter, y, is estimated as a function of the temperature is shown to follow the equation y""a(T- T 0). Vogel-Fulcher- Tammann equation fits the data le relaxation peak frequency as a function of the inverse of absolute temperature for the various tures quite well, this being possibly a consequence of the temperature dependence of the ched exponential parameter. The predictions from the mode coupling theory and those by rand and Souletie are verified with the exception that the exponent is found to be much greater predicted by these theories. The relative predominance of the Iohari-Goldstein process in myl bromide increases initially with dilution with 2-methylpentane and then disappears as the ber density of the independent relaxors increases with further dilution.