Heat capacity anomalies along the critical isotherm in fluid-fluid phase transitions

resumo

The behavior of the isochoric heat capacity of pure fluids and the isobaric heat capacity at constant composition of binary mixtures along isothermal paths of approach to liquid-gas and liquid-liquid critical points is studied. From the complete scaling formulation of fluid-fluid criticality, explicit expressions for the critical amplitudes of the leading vertical bar Y-Y-c vertical bar(-alpha/beta) (where Y can be the density or the mole fraction) contributions are found to reveal previously discovered features of the scaling function, whereas the nature of the most important asymmetry-related terms is characterized. Data for pure toluene and for the binary mixture nitromethane-isobutanol are described within experimental uncertainty using the vertical bar Y-Y-c vertical bar(-alpha/beta) singularity plus a linear term. Extensive data for mixtures allow proper visualization of the topological features of the heat capacity-density-temperature surface in the critical region.

palavras-chave

CRITICAL END-POINTS; LIQUID; THERMODYNAMICS; UNIVERSALITY

categoria

Chemistry; Physics

autores

Losada-Perez, P; Perez-Sanchez, G; Troncoso, J; Cerdeirina, CA

nossos autores

agradecimentos

This research was supported by the Conselleria de Innovacion e Industria (Xunta de Galicia) under Grant No. PGIDIT-06PXIB3832828PR. Assistance to P.L.-P. and G.P.-S. by the "Ministerio de Educacion y Ciencia" under the "Programa Nacional de Formacion del Profesorado Universitario" (Grant Nos. AP-2004-2947 and AP-2005-1959, respectively) is greatly appreciated.

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