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

Abstract

Measurements have been made at the critical mixing composition of the system 2,6-lutidine-water for a (Tc-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 Ic−1(0) ∝ (ε)(1.26± 0.02),ξs=(2.0± 0.2)(ε)−(0.61± 0.08) Å,D=(0.290± 0.020)(ε)(0.554± 0.015)× 10−5cm2/sec,ξΓ=(2.92± 0.19)(ε)−(0.567± 0.015) Å,where ε =(Tc-T)/Tc, Ic(0) is the intensity extrapolated to zero angle, ξΓ the correlation length from intensity measurements, D the mutual diffusion coefficient, and ξΓ 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 (Tc-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 γ - psi = ν seems to be valid with ν=νs=νΓ. We also find that the excess shear viscosity does not exhibit a simple power law dependence on (Tc-T) as the critical temperature is approached.