Physics and Chemistry of Liquids Vol. 50, No. 2, March–April 2012, 210–221 Thermoacoustical study of molecular interactions in binary mixtures of pentane with methanol and tert-butanol Shashi Singh * , Maimoona Yasmin, Divya Shukla, Shahla Parveen and Manisha Gupta Department of Physics, University of Lucknow, Lucknow 226007, India (Received 3 May 2011; final version received 15 May 2011) Experimental values of density, ultrasonic velocity and viscosity for the binary mixtures of pentane with methanol and tert-butanol have been measured at 293.15, 298.15 and 303.15 K over the entire composition range. Using these experimental data, specific heat ratio, heat capacity, effective Debye temperature, pseudo-Gru¨neisen parameter, viscosity deviation, excess internal pressure, excess Gibb’s free energy of activation for viscous flow and excess molar enthalpy have been calculated and computed results were fitted to the Redlich-Kister polynomial equation. These parameters were used to study the nature and extent of intermolecular interaction between components molecules present in the binary mixtures. The results suggest that stronger specific interactions are taking place in pen- tane þ methanol mixture than in pentane þ tert-butanol mixture. Furthermore, various empirical relations were used to correlate the ultrasonic velocities of these mixtures. An excellent agreement has been found between experimental and theoretical values. Keywords: specific heat ratio; Debye temperature; pseudo-Gru¨neisen parameter; methanol; tert-butanol PACS numbers: 62.60.þv; 65.20.-w; 66.20.-d 1. Introduction Study of liquid mixtures has gained considerable interest in recent years. The density, viscosity and ultrasonic velocity are important properties of pure liquids as well as liquid mixtures for design of separation equipment [1–4]. In recent years, there has been considerable interest in experimental and theoretical investigations of the excess thermodynamic properties of binary mixtures [5,6]. In principle, the interaction between the molecules can be established from the study of the characteristic departure from ideal behaviour of some physical properties (i.e. viscosity, energy and enthalpy etc.). Ultrasonic data for liquid mixture have also yielded information regarding the nature of interaction forces operating within and between the molecules and the existence of a complex, if any [7,8]. The study of atomic motions in liquids plays a significant role in understanding the solid-like behaviour of liquids. The dynamical behaviour of liquids can be studied *Corresponding author. Email: shashi.cmpl@gmail.com ISSN 0031–9104 print/ISSN 1029–0451 online ß 2012 Taylor & Francis http://dx.doi.org/10.1080/00319104.2011.597030 http://www.tandfonline.com