DIELECTRIC-RELAXATION OF 3-BROMOPENTANE IN MIXTURES WITH 3-METHYLPENTANE

Dielectric measurements of mixtures of 75, 50 and 25 mol% 3-bromopentane (3BP) in 3-methylpentane are presented in the temperature range 85-112 K. The data obtained from ac and transient measurements are in the frequency range from 100 kHz to below 1-mu-Hz (transient data are transformed to the frequency domain). Previous dielectric studies and a recent measurement on pure 3BP fit the Cole-Davidson (CD) skewed arc within the limits of the experiment. However, measurements reported here on the mixtures yield a better fit to the Kohlrausch-Williams-Watts (KWW) function than to the CD skewed arc. A log plot of best-fit KWW relaxation times (KWW-tau) against reciprocal temperature appears to be linear for the temperature range of the measurements (all mole fractions) unlike the Vogel-Tammann-Fulcher behavior of pure 3BP. Due to the limited temperature range, only a comparison of isothermal relaxation times between adjacent concentrations can be made directly: at 111 K, the KWW-tau for pure 3BP is 2.5 s and that for 75% 3BP is 0.0018 s; at 100 K, the KWW-tau for 75% 3BP is 104 s and that for 50% is 0.0687 s; at 90.9 K, the KWW-tau for 50% 3BP is 402 s and that for 25% is 0.444 s.