Dielectric relaxation spectroscopy of 2-propanol-water mixtures

Abstract

The complex dielec. spectra of 2-propanol-water mixts. were detd. at seven molar fractions of 2-propanol, X=0.03, 0.065, 0.14, 0.3, 0.5, 0.7, and 0.9 at 25°C in the frequency range 0.1≤ν/GHz≤89 with the help of time domain reflectometry in 0.1≤ν/GHz≤25 and waveguide interferometry in 13≤ν/GHz≤89. In the alc.-rich region of 0.3≤X≤1.0, a description of the ε*(ν) spectra requires the superposition of the three relaxation processes. The dominating low-frequency dispersion (j=1) follows a Cole-Cole equation. Addnl., two Debye equations (j=2 and 3) with the relaxation times of τ2∼10-20 ps and τ3∼1-2 ps are required to fit the high-frequency part of the spectrum. The three processes are assigned to the cooperative dynamics of the H-bond system (j=1), a rotation of singly H-bonded alc. monomers at the ends of chainlike structure (j=2), possibly connected to the formation of bifurcate hydrogen bonds, and a flipping motion of free OH group (j=3). In the region of X<0.3, the intermediate alc. monomer process becomes inseparable. Here, a two process model with a Cole-Cole equation for the main dispersion and a high-frequency Debye process for the fast switching mode gives the best fit. Based on the dielec. relaxation mechanism of the pure constituents proposed in the literatures [J. Barthel et al., Chem. Phys. Lett. 165, 369 (1990), and R. Buchner et al., Chem. Phys. Lett. 306, 57 (1999)], a compn.-dependent relaxation behavior of the mixts. is discussed.