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5.5 Ultrasonic spectrometry

Figure 5.20: Scaling function data FBF of the binary mixture (ET-DOD) of critical con- tribution: without taken into account of the additional noncritical contribution.

found in both mixtures, with consequences for the data evaluation. In Fig.(5.20) the scal- ing function (ET-DOD) data, following on the assumption of a system without additional chemical relaxation are displayed. These data, follow the general trends in the scaling function but show systematic deviations and a large scatter. Moreover, the critical am- plitude SBF as adjustable parameter similar to (NE-CH) demonstrates a dependence on temperature. However, taking into account the existence of an additional Debye-type re- laxation term and considering its contribution to the low frequency wing in the spectra f < 1.7MHz according to Eq.(4.26), leads to an excellent agreement of the experimen- tal scaling function with the theoretical form of the Bhattacharjee-Ferrell model. It also leads to independency of the critical amplitude on temperature. The same procedure has been successfully performed with the binary mixture (ME-HEX) [93] as well as with the system perfluoromethylcyclohexane-carbon tetrachloride [100]. Unfortunately, although recently performed measurements on a (NE-CH) mixture of noncritical composition point at an additional chemical relaxation. The unusual behavior of the critical amplitude of that system is still not clear.

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