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 scannin g, adiabatic calorimeter. Two data runs are analyzed to provide heat c apacity and enthalpy data that are fitted by equations with background terms and a critical term that includes correction to scaling. The cr itical exponent alpha was determined to be 0.107+/-0.006, consistent w ith theoretical predictions. When alpha was fixed at 0.11 to determine various amplitudes consistently, our values of A(+) and A(-) agreed w ith a previous heat capacity measurement, but the value of A(+) was in consistent with values determined by density or refractive index measu rements. While our value for the amplitude ratio A(+)/A(-)=0.56+/-0.02 was consistent with other recent experimental determinations in binar y liquid mixtures, it was slightly larger than either theoretical pred ictions or recent experimental values in liquid-vapor systems, The cor rection to scaling amplitude ratio D+/D-=0.5+/-0.1 was half of that pr edicted. As a result of several more precise theoretical calculations and experimental determinations, the two-scale-factor universality rat io X, which we found to be 0.019+/-0.003, now is consistent among expe riments and theories. A new ''universal'' amplitude ratio R(BCr)(+/-) involving the amplitudes for the specific heat was tested. Our determi nation of R(BCr)(+)=-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 bina ry fluid mixture. (C) 1996 American Institute of Physics.