Light Scattering and Shear Viscosity Studies of the Binary System 2,6-Lutidine-Water in the Critical Region

Measurements have been made at the critical mixing composition of the system 2,6‐lutidine‐water for a (T_c‐T) range of 0.001°–7.5°C for the intensity and Rayleigh linewidth and of 0.007°–27.4°C for the shear viscosity. We find that $$\begin{array}{c}{I}_c^{\text{−1}}{\text{(0)\hspace{0.17em}∝ (ε)}}^{\text{(1.26± 0.02)}},\\ {\xi }_s{\text{=(2.0± 0.2)(ε)}}^{\text{−(0.61± 0.08)}}\mathrm{\AA ,}\\ {\text{D=(0.290± 0.020)(ε)}}^{\text{(0.554± 0.015)}}{\text{× 10}}^{\text{−5}}{\mathrm{cm}}^2/\sec ,\\ {\xi }_{\Gamma }{\text{=(2.92± 0.19)(ε)}}^{\text{−(0.567± 0.015)}}\mathrm{\AA ,}\end{array}$$ where ${\mathrm{\epsilon \; =(T}}_c{\mathrm{‐T)/T}}_c{\mathrm{,\hspace{0.17em}\; I}}_c\text{(0)}$ is the intensity extrapolated to zero angle, ξ_Γ the correlation length from intensity measurements, D the mutual diffusion coefficient, and ξ_Γ the correlation length obtained from fitting the Kawasaki equation to linewidth measurements with the above value of D. We find that the Ornstein‐Zernike‐Debye theory is valid for (T_c‐T) >0.03°C and the Kawasaki mode‐mode coupling theory gives a good over‐all description of the behavior of the linewidth of the Rayleigh line. The Kadonoff‐Swift‐Kawasaki result $\mathrm{\gamma \; ‐\hspace{0.17em}psi\; =\; \nu }$ seems to be valid with ${\mathrm{\nu =\nu }}_s{\mathrm{=\nu }}_{\Gamma }.$ We also find that the excess shear viscosity does not exhibit a simple power law dependence on (T_c‐T) as the critical temperature is approached.