6 Discussion of the Dynamic Scaling Hypothesis
6.1 Comparison of Ultrasound (US) and Dynamic Light Scattering (DLS) Results
The relaxation rates determined from dynamic light scattering and ultrasound measurements show excellent agreement:
As already mentioned in the preceding section, the scaling function was verified using a fixed value of Ω1/2 = 2.1. It is therefore not meaningful to claim that the fitting procedure independently confirmed this parameter. It is noteworthy, however, that during the development of the theory the parameter was not always quoted with this value; Ω1/2 = 2.5 was also used in some cases.
The 20% uncertainty in Γ0US arises because ultrasound measurements very close to the critical point are difficult, while the theory is valid only sufficiently near that point. Figure 6.1 summarizes the results.
6.2 Fitting Methods and Their Significance
Before the final determination of the Bhattacharjee–Ferrell scaling function, it was necessary to examine different fitting methods and their effects on the final result. For example, one may prescribe the relaxation time measured by light scattering and examine how the fit develops. If the amplitude ABF is assumed to be independent of temperature, or only weakly temperature-dependent, and is normalized at all temperatures (see Eq. 6.1), a very good agreement with the theoretical scaling-function curve is also obtained. This comparison is shown in Figure 6.2.