Abstract
We have investigated the (K+, Cl-) ions effect on the refractive index (n), on the mass density ($\rho$) and on the shear viscosity ($\eta$) in the homogeneous phase above the higher critical solution point in critical-composition liquid mixture isobutyric acid + water (I-W). For the pure critical system (I-W), both critical exponents ($\alpha$) and $y$, respectively obtained by the techniques of density ($\rho$) and refractive index (n) on the one hand, and by shear viscosity ($\eta$) on the other hand, agree well with (d = 3)-dimensional Ising value established not only by renormalisation group (RG) calculation, but also by extensive high-T series expansions and Monte Carlo simulations. Concerning the exponent , with (K+, Cl-) ions at weak concentrations, the critical mixture (I-W) exhibits critical behaviour in favour of Ising critical exponent asymptotically close to the critical point. However, the critical exponent y value connected to the critical anomaly of shear viscosity is found smaller than the one predicted by dynamic renormalisazation group and mode-coupling theories. Furthermore, the decrease of the critical amplitude of the viscosity caused by the ionic impurity is attributed to the strengthening of the solute-solvent interaction which causes the increase of the water-solute clusters.
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