Oscillations, Waves, and Interactions - GWDG

Liquids: Formation of complexes and complex dynamics 393
Figure 24. Shear viscosity ηs of the nitroethane-3-methylpentane mixture of critical composition
displayed versus temperature T [111]. Circles show previous data [121]. The full
curve is the graph of the theoretical ηs relation (Eq. (63)), the dashed line represents the
noncritical background contribution ηs (Eq. (64)).
of H is given elsewhere [115,116]. Use of the more recent H ′ crossover function [118]
does not noticeably change the data obtained from the evaluation procedure. The
individual parameters Aη, Bη, and Tη in Eq. (64) are characteristic of the system
under consideration.
The mutual diffusion coefficient
�
�1 2 2
D = DKF + b x �Zη/2 RΩK(x) + 3πηs 1 + x
16ηb
2
ξ
� −1
˜q c − q −1�
D
�
depends also on parameters ξ, qc, and qD. Here x = q ξ with q denoting the amount
of the wave vector selected by scattering geometry in the dynamic light scattering
measurements. Furtheron, b = 0.55, R = 1.03, ˜q −1
c = q−1 c + (2qD) −1 , and
ΩK(x) = 3
4x2 �
1 + x 2 + (x 3 − x −1) �
) arctan x
is the Kawasaki function [119]. Using Eq. (45) with ˜ν = 0.63 the unknown parameters
ξ0, qc, qD, Aη, Bη, and Tη follow from a simultaneous regression analysis of the shear
viscosity and diffusion coefficient data. An example of shear viscosity data and their
representation by Eq. (63) is presented in Fig. 24. Figure 25 shows the relaxation
rates following from the shear viscosity and dynamic light scattering results. This
diagram also indicates the adequacy of the power law (Eq. (60)). For the same
binary system the scaling function data resulting from Eq. (62) are shown in Fig. 26,
indicating that the Bhattacharjee-Ferrell scaling function represents the experimental
data within their limits of experimental errors. The same result has been found
for the other systems investigated. The parameter values for these systems vary
between ξ0 = 0.145 nm and Γ0 = 187 · 10 9 s −1 , n-pentanol-nitromethane [109], and
(65)
(66)