A dielectric relaxation study of some mixtures of mono and dihydric alcohols

Dielectric spectra up to 72 GHz have been measured at 20 degrees C for binary mixtures of a monohydric and a dihydric alcohol, composed from the following groups of substances. Monoalcohols: l-butanol and tert-butanol. Diols: Ethanediol, 1,2- and 1,3-propanediol, 1,2- and 1,4-butanediol, 1,2- and 1,5-pentanediol. The spectra are rather similar in shape. They are formally described by four Debye type spectral components. The principal (lowest frequency) component, which is related to the dynamics of self and/or hetero-association, is discussed with respect to steric conditions. In mixtures of l-butanol with longer chain 1,2-diols, the principal relaxation time passes through a minimum on increasing the diol content. In mixtures of tert-butanol (which has a weaker self-association tendency) with longer chain 1,n-diols, on the other hand, it passes through a maximum. With regard to the principal relaxation strength, longer chain 1,2-diols tend to resemble monohydric alcohols of full diol chain length while 1,n-diols tend to resemble monohydric alcohols of half the diol chain length. (C) 1999 Elsevier Science B.V. All rights reserved.