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5.5 Ultrasonic spectrometry

Figure 5.11: Frequency normalized ultrasonic attenuation spectra for the (NE-CH) mix- ture of critical composition at three temperatures:(▲): 28.3 oC , (■):25.6 oC, (•): 24.0 oC.

exceptionally large. According to the Bhattacharjee-Ferrell theory the scaling function FBF(Ω) can be derived, rewriting Eq.(4.25) as ratio:

Usually, it is assumed that the temperature dependence in the sound velocity cs and also in the amplitude A of the attenuation coefficient is sufficiently small to be neglected so that F∗ BF = 1 can be used in Eq.(5.14), as originally proposed by Bhattacharjee and Ferrell. This precondition, however, is not always fulfilled. A closer examination of the binary critical mixture (NE-CH) points at an unusual dependence of the critical amplitude SBF on temperature [90]. In the next section this amplitude behavior will be discussed with more details. Moreover, for (ME-HEX) as well as (ET-DOD) it has been found that, al- though both considered constituents of the binary systems do not reveal indications of a chemical relaxation in pure liquids, the mixture indicates a relaxation due to an alco-

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