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The Yang-Yang anomaly in nitromethane and 3-pentanol binary liquid mixture: Experimental search by adiabatic scanning calorimetry


P. Losada-Perez1, C. Tripathi1, J. Leys1, C. Glorieux1 and J. Thoen1

1Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde Katholieke Universiteit Leuven, Heverlee, Belgium

Keywords: Yang-Yang anomaly, liquid-liquid criticality, adiabatic scanning calorimetry
property: isobaric heat capacity
material: binary liquid mixture

The intrinsic asymmetric character of fluid-fluid criticality is accounted for by the so-called complete scaling formulation introduced by Fisher and coworkers for liquid-gas critical points [1] and later extended by Cerdeirina et al. to liquid-liquid critical points [2]. The most relevant consequences of complete scaling are the appearance of novel singularities for the coexistence curve diameter of density variables (conjugated to a field), as well as the existence of the so-called Yang-Yang anomaly [3], related to the behavior of the heat capacity in the two-phase region. The Yang-Yang relation for binary mixtures in the two-phase region reads [2]:

Cp,x2 = -T (d2mu1/dT2)p,x2-Tx2(d2mu/dT2)p,x2 (1)

where mu1 is the chemical potential of component 1, mu is the chemical potential difference of the two components of the mixture, x2 is the mole fraction of component 2 and Cp,x2 is the two-phase isobaric heat capacity at a given mole fraction. A Yang-Yang anomaly in liquid-liquid criticality implies that both terms in the right-hand side of Eq. (1) should diverge. The Yang-Yang anomaly in liquid-liquid criticality has remained elusive due to the need of very accurate (and time-consuming) measurements in the two-phase region and the need for a system with a large heat capacity critical anomaly. In this context, adiabatic scanning calorimetry (ASC) proves to be the most adequate high-resolution technique to accomplish such a task [4]. In addition, a UCST-type binary mixture (nitromethane and 3-pentanol) with a large heat capacity anomaly has been recently found [5]. We report on high-resolution Cp,x2 data of nitromethane and 3-pentanol at different isopleths and temperature interval (286.15-296.15) K. From the obtained data we have constructed a Yang-Yang plot, i.e. a graphical representation of Cp,x2 vs x2 for a number of isotherms, from which we observed the divergence of both contributions in Eq. (1).

References
  1. Y.C. Kim, M.E. Fisher and G. Orkoulas, Phys. Rev. E 67 061506 (2003)

  2. C.A. Cerdeiriña, M.A. Anisimov and J.V. Sengers, Chem. Phys. Lett. 424, 414 (2006).

  3. C.N. Yang and C.P. Yang, Phys. Rev. Lett. 14, 303 (1964)

  4. J. Thoen, in Heat Capacities: Liquids, Solutions and Vapours, edited by E. Whilhem and T. M. Lechter (The Royal Society of Chemistry, London, 2010) Chap. 13

  5. P. Losada-Pérez, C.S. Pati Tripathi, J. Leys, C. Glorieux, and J. Thoen, J. Chem. Phys. 134, 044505 (2011)

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