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5.3 Binary systems without and with one additional noncritical relaxation term

Figure 5.3: Density of the binary system triethylamine-water of critical composition with lower critical temperature.

5.3.2 Dynamic light scattering, shear viscosity ηs and characteristic relaxation rate Γ0

As mentioned in the previous section, in order to reduce the number of unknown parame- ters, ultrasonic spectrometry has been complemented by the dynamic light scattering and shear viscosity measurements. The lifetime of critical fluctuations τξ has been determined by dynamic light scattering and the shear viscosity measurements as presented in Chapter (2). The shear viscosity has been measured as a function of temperature using an capil- lary and a falling ball viscosimeter. These two methods have been used to complement each other as well as to control the shear rate dependence in ηs. In the (NE-CH) system it was found that the shear rate dependence in the viscosity data is within the limits of experimental errors ∆ηs/ηs = 0.02. Both methods of measurements agree with one other as is shown by the data in Fig.(5.5). However, in order to carefully treat the capillary viscosimeter data, the shear rate corrections have to be taken into account. Those correc- tions have to be performed, because the critical temperature close to the consolute point changes due to macroscopic non-linear effects. The relation between geometrical param- eters of the capillary and the shear rate was given by Kohlrausch:

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