Critical behavior of 2,6-dimethylpyridine-water: Measurements of specific heat, dynamic light scattering, and shear viscosity

The specific heat C p at constant pressure, the shear viscosity η s , and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature T c . The amplitude of the fluctuation correlation length ξ 0 = ( 0.198 ± 0.004 ) nm has been derived from a combined evaluation of the η s and D data. This value is in reasonable agreement with the one obtained from the amplitude A + = ( 0.26 ± 0.01 ) J ∕ ( g K ) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Γ of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Γ = ( 25 ± 1 ) × 10 9 s − 1 . No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity η b , resulting from the treatment of η s and D data, with the viscosity η s ( ν = 0 ) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5 - 130 MHz using a novel shear impedance spectrometer.