MICROHETEROGENEITY OF 2-BUTOXYETHANOL WATER MIXTURES AT ROOM-TEMPERATURE - AN ULTRASONIC RELAXATION STUDY

At 25-degrees-C the ultrasonic absorption coefficient of 2-n-butoxyeth anol/water mixtures has been measured as a function of frequency nu (1 00 kHz less-than-or-equal-to v less-than-or-equal-to 2 GHz) and mass f raction y (0 < y less-than-or-equal-to 1). Various relaxation function s have been fitted to the measured spectra. It was found that (1) a su m of four Debye terms with discrete relaxation times is appropriate to represent the excess absorption, but also (2) a sum of two Debye term s and a Romanov-Solov'ev, Fixman, or Kawasaki term reflecting concentr ation fluctuations, or (3) a sum of a high-frequency Debye term and on e term due to viscous boundary and thermal conductivity effects in het erogeneous media, respectively. Consistent behaviour of the parameters is best obtained for the latter spectral function. The parameter valu es of this function indicate how the second phase is dispersed. The ma ximum value of the effective radius of this (micro-)phase domains amou nts to 130 nm. It is adopted around the critical composition of the bi nary liquid system. The dependence upon concentration in the relaxatio n rate of the high-frequency Debye term suggests a mechanism of struct ural isomerization of butoxyethanol molecules. Both, the microheteroge ncity and the isomerization effect are discussed together with other p roperties of the liquids to get an almost comprehensive view of the st ructure, kinetics, and microdynamics of this interesting binary aqueou s system.