Effect of ionic additives on critical exponents of 2,6-dimethylpyridine–water

The diffusion coefficients and the shear viscosities of critical mixtures of water and 2,6-dimethylpyridine have been measured without and with small amounts of an ionic liquid or sodium bromide added. The experimental data reveal significant deviations from universal power law behaviour and also a dependence of the critical exponents on the concentration and properties of the added ions. A coupling of the critical fluctuations in the local concentrations to the formation of mesoscopic molecular aggregates is suggested. Likely the formation involves stacking of the cyclic amine molecules promoted by hydrophobic interactions and hydrogen bonding with water.