8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P2.47Experimental evidence for the Yang-Yang anomaly in abinary liquid mixture: high-resolution study by adiabaticscanning calorimetryPatricia Losada-Perez, 1 ChandraShekhar Pati Tripathi, 1 Jan Leys, 1 ChristGlorieux, 1 and Jan Thoen 11 Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001, Heverlee, BelgiumThe Yang Yang relation for binary liquid mixtures in the two phase region expresses the isobaricheat capacity at constant mole fraction, Cp, x2, as a linear function of the mole fraction x2,the slope being proportional to the second temperature derivative of the chemical potentialdifference between the two components and the intercept to the second temperature derivativeof the chemical potential of one of the components [1]. It is well known that Cp, x2 diverges atthe liquid liquid critical point. According to the Yang Yang relation at least one of the two termsshould diverge. Classical scaling predicts that only the intercept diverges. However, the YangYang anomaly predicted by complete scaling formulation implies that both terms should diverge[2]. Such anomaly has remained elusive in liquid liquid criticality due to the need of very accurateand time consuming measurements in the two phase region and the need for a system with a largeheat capacity anomaly. Adiabatic scanning calorimetry proves to be the adequate high resolutiontechnique to accomplish such a task. Moreover, a UCST type of binary mixture (nitromethane and3 pentanol) with a large heat capacity anomaly has been recently found. We report high resolutionCp, x2 data for this system at different isopleths between 286 and 296 K. A Yang Yang plot, i.e. a representation of Cp, x2 vs x2 for various isotherms has been performed. It is observed thatboth slope and intercept diverge near the critical point. The experimentally detected Yang Yanganomaly is studied in the framework of the predictions of complete scaling.[1] C. A. Cerdeirina, M. A. Anisimov, and J. V. Sengers, Chem. Phys. Lett. 424, 414(2006).[2] 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 13.47