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5 Experimental Verification of Dynamic Scaling Theories and Discussions

Figure 5.23: Half-power bandwidth ∆fr of an acoustical resonance at 4000 kHz of a cylindrical biplanar resonator filled with the (i−C4E1/H2O) mixture of critical compo- sition, plotted versus reduced temperature ε.

Figure 5.24: Relaxation rate ΓDLS, (◦), and non-universal be- havior of ΓUS, (•), near critical point.

The relaxation rate Γ of concentration fluc- tuations, derived from the critical contribu- tion to the ultrasonic spectra, did not follow power law Fig.(5.24) as did the Γ values from static and dynamic light scattering [112]. There- fore, additional measurements of low frequency part of the ultrasonic spectra have been per- formed between 200 kHz and 3 MHz and have been evaluated on the assumption that the re- laxation rate of critical fluctuations in ultra- sonic spectra is governed by the relaxation rate ΓDLS from the dynamic light scattering. An example of an ultrasonic excess attenua- tion spectrum of the (i−C4E1/H2O) mixture of critical composition at 25 oC is displayed in Fig.(5.25). A careful analysis of the broadband sonic (i−C4E1/H2O) spectra at Yc lead to the conclusion that at least three relaxation terms,

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