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5 Experimental Verification of Dynamic Scaling Theories and Discussions

Figure 5.16: Half-attenuation frequency Ωx 1/2 for the Bhattacharjee-Ferrell empirical scaling function (x = BF) plotted versus scaled frequency: (◦) data for the system (ET- DOD). (□) refers to (ME-CH) mixture of critical composition.

confirms the conclusion that the Bhattacharjee-Ferrell scaling function applies best to the experimental data. Results for most binary critical systems measured in present thesis indicate ΩBF 1/2 = 2.1±0.1. This value is in nice agreement with the theoretical prediction of Bhattacharjee and Ferrell. For the system (n-PE-NM) the half-attenuation frequencies are somewhat smaller (ΩBF 1/2 = 1.8). Previous investigations of the system (ET-DOD) had revealed a value (ΩBF 1/2 = 1.2) [89]. However, if effects of hydrodynamic coupling are taken into account ΩBF 1/2 = 2.1 follows [99].

Another binary liquid, which has been studied within the series of mixtures without ad- ditional noncritical relaxation, was the system (NE-CH). This critical mixture, however, reveals an anomaly in the critical amplitude SBF Eq.(4.17) and in the adiabatic coupling constant g. As was mentioned previously, the assumption of the independency from tem- perature not fulfilled with these systems. If the critical amplitude is assumed constant, the data show systematic deviations from the theoretical FBF function in a way that most of them seem to be shifted to lower reduced frequency Ω(Fig.(5.18)). Since, the more recent

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