Heat capacity anomaly near the lower critical consolute point of triethylamine–water

The heat capacity of the binary liquid mixture triethylamine–water has been measured near its lower critical consolute point using a scanning, adiabatic calorimeter. Two data runs are analyzed to provide heat capacity and enthalpy data that are fitted by equations with background terms and a critical term that includes correction to scaling. The critical exponent α was determined to be 0.107±0.006, consistent with theoretical predictions. When α was fixed at 0.11 to determine various amplitudes consistently, our values of A + and A− agreed with a previous heat capacity measurement, but the value of A+ was inconsistent with values determined by density or refractive index measurements. While our value for the amplitude ratio A+/A −=0.56±0.02 was consistent with other recent experimental determinations in binary liquid mixtures, it was slightly larger than either theoretical predictions or recent experimental values in liquid-vapor systems. The correction to scaling amplitude ratio D+/D −=0.5±0.1 was half of that predicted. As a result of several more precise theoretical calculations and experimental determinations, the two-scale-factor universality ratio X, which we found to be 0.019±0.003, now is consistent among experiments and theories. A new ‘‘universal’’ amplitude ratio RBcr± involving the amplitudes for the specific heat was tested. Our determination of RBcr+=−0.5±0.1 and R Bcr−=−1.1±0.1 is smaller in magnitude than predicted and is the first such determination in a binary fluid mixture.

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