Competition of Viscosity Correlation Equations in Isobutyric Acid plus Water Binary Mixtures Near and Far Away from the Critical Temperature

Shear viscosity deviations Delta eta have been investigated by using density (rho) and kinematic viscosity (nu) measurements for isobutyric acid + water (IBA + W) mixtures over the entire range of mole fractions at atmospheric pressure and at two temperatures (301.15 and 315.15 K). This study extends the temperature range from the five other temperatures investigated in a previous work, 1.055 Ka parts per thousand currency sign(T-T (c) )a parts per thousand currency sign14.055 K, both far from and close to the critical temperature. This system exhibits very large positive values of Delta eta due to increased hydrogen bonding interactions and the correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The results were also fitted with the Redlich-Kister polynomial equations and the recently proposed Herraez correlation equation. Comparisons between the two models at different temperatures and number of parameters are discussed. We note that, in this system where the shear viscosity eta as a function of mole fraction (x (1)) of IBA presents a maximum, experimental data are in agreement with the two correlation models when more than three parameters are employed, especially for temperatures far from the critical temperature.