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5.6 Systems with complex background contributions

the temperature dependence of the low-frequency term (n = 2 in Eq.(5.23)), within the limits of experimental error, can be represent by a power law. Applying the relation de- fined by Eq.(5.23) yields τD0,2 = 31.19 ns and ψ = 0.17±0.04. This value of the critical exponent is in fair agreement with that from the system isobutyric acid-water [128], where Kaatze at al. obtained the exponents ψ = 0.2 ± 0.05 and ψ = 0.3 ± 0.2. In Fig.(5.36) a bilogarithmic plot of τD2 as a function of reduced temperature ε is given. The unusual

Figure 5.37: Scaling function data for the (TEA-H2O) system as calculated from runs special low frequency measurements and from previous broadband spectrometry [97] are indicated by figure symbols. (run 1 (•), run 2 (▲), run 3 (▼), previous (◦)) The line is the graph of the empirical form of the Bhattacharjee-Ferrell scaling function.

coupling of the rotational isomerization to the critical fluctuations reflected thereby may be also be explained within the framework of the afore mentioned redistribution of solvent molecules associated with structural isomerization of TEA with water. More detailed, the ethylene groups parts of TEA are surrounded by cages of water molecules. The H-bond network of water molecules will fluctuated slower in these cages (”hydrophobic hydra- tion”), which results in a higher viscosity. The Debye-Stokes-Einstein model, which pre- dicts a linear relation between the rotational diffusion time of a solute molecule, τrot and viscosity ηs, may give an explanation for such effect:

where V denotes the effective molecular volume. Unfortunately, the shear viscosity data

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