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 bina ry mixtures of a monohydric and a dihydric alcohol, composed from the follo wing 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 d escribed by four Debye type spectral components. The principal (lowest freq uency) component, which is related to the dynamics of self and/or hetero-as sociation, 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-butan ol (which has a weaker self-association tendency) with longer chain 1,n-dio ls, on the other hand, it passes through a maximum. With regard to the prin cipal relaxation strength, longer chain 1,2-diols tend to resemble monohydr ic alcohols of full diol chain length while 1,n-diols tend to resemble mono hydric alcohols of half the diol chain length. (C) 1999 Elsevier Science B. V. All rights reserved.