The specific heat anomaly in some ternary liquid mixtures near a critical solution point

Abstract

The anomaly in the specific heat at constant pressure and constant overall concentration Cpx has been investigated near a critical solution point in a ternary system of triethylamine–water–heavy water and in two different mixtures of triethylamine–water–ethanol. Data have been obtained by means of a standard heat pulse technique and with a constant heating rate method. Accurate results could be obtained for ‖TC−T‖/Tc values as small as 10−5. A detailed analysis of the data has been carried out by means of a nonlinear least squares fitting procedure. No indication of exponent renormalization was observed for triethylamine–water–heavy water. Instead, the value for the critical exponent as well as for the universal amplitude ratio are in close agreement with recent values obtained for the binary system triethylamine–heavy water and with the Ising values. For the two critical mixtures of triethylamine–water–ethanol exponent renormalization effects were, however, clearly visible and increased with increasing ethanol concentration. The effect was much more pronounced in the two-phase region. Although effective exponent values smaller than the Ising value αI = 0.110 were obtained, the data were not compatible with αR = −αI/(1−αI), indicating that for the experimental range the full renormalization regime was not yet reached. The experimental observations do not contradict the theoretical estimates of crossover between αI and αR.