Fluid Phase Equilibria 294 (2010) 157–179 Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid Studies on the density, heat capacity, surface tension and infinite dilution diffusion with the ionic liquids [C 4 mim][NTf 2 ], [C 4 mim][dca], [C 2 mim][EtOSO 3 ] and [Aliquat][dca] Carlos A. Nieto de Castro a,c,∗ , Elisa Langa a , Ana L. Morais a , Manuel L. Matos Lopes a,c , Maria J.V. Lourenc ¸o a,c , Fernando J.V. Santos a,c , M. Soledade C.S. Santos b,c , José N. Canongia Lopes d , Helena I.M. Veiga d , Mafalda Macatrão d , José M.S.S. Esperanc ¸a d , Carolina S. Marques e , Luís P.N. Rebelo d , Carlos A.M. Afonso e a Centro de Ciências Moleculares e Materiais, Faculdade de Ciências, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal b Centro de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal c Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal d Instituto de Tecnologia Química e Biológica, ITQB2, Universidade Nova Lisboa, Av. República, Apartado 127, 2780-901 Oeiras, Portugal e CQFM - Centro de Química-Física Molecular and IN - Institute of Nanosciences and Nanotechnology, Instituto Superior Técnico, 1049-001 Lisboa, Portugal article info Article history: Received 7 December 2009 Received in revised form 3 March 2010 Accepted 6 March 2010 Available online 12 March 2010 Keywords: Ionic liquids Density Diffusion Heat capacity Heat storage capacity Heat transfer fluids Surface tension Thermal expansion coefficient Isothermal compressibility abstract Ionic liquids are a class of fluids that requires the attentions of experimentalist and theoreticians. In a new project on synthesis and characterization of new and not-so-new ionic liquids, the study of several thermophysical properties of these liquids was started, namely binary diffusion, electri- cal conductivity, heat capacity, surface tension, viscosity and thermal conductivity. Among others we will study 1-n-butyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, ([C 4 mim][NTf 2 ]), 1-n- butyl-3-methyl-imidazolium dicyanamide, ([C 4 mim][dca]), 1-ethyl-3-methyl-imidazolium ethylsulfate, ([C 2 mim][EtOSO 3 ]) and methyltrialkylammonium dicyanamide [Aliquat ® 336-derived][dca], and in the case of diffusion, their mixtures with water. It is the purpose of this paper to report data on the density, using vibrating tube densimetry, infinite dilution diffusion coefficients, using the Taylor dispersion method, heat capacity, using DSC equip- ment and surface tension, using the Wilhelmy plate method. Density measurements were performed at atmospheric pressure between 293 and 363 K and several isotherms, depending on the stability of the compound, up to 60 MPa, with an uncertainty of 0.4%. Measurements were performed at 298.03 K for the infinite dilution measurements, with an uncertainty of 1.3–3.5%, for temperatures between 300 and 370 K for heat capacity, with an uncertainty better than 1.5%, and between 292 and 395 K for surface tension, with an uncertainty of 1.5–1.8%. A brief analysis of the potential of the fluids studied as engineering heat transfer fluids, namely its heat storage capacity was also performed. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Ionic liquids have proven to be safe and sustainable alternatives for many applications in industry and chemical manufactur- ing. Their success arises mainly from their thermophysical and phase-equilibria properties, and the versatility of their synthe- sis, manageable to be tailored for a given application. Their ∗ Corresponding author at: Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal. Tel.: +351 217 500 918; fax: +351 217 500 088. E-mail address: cacastro@fc.ul.pt (C.A. Nieto de Castro). solvent properties as well as their heat transfer/heat storage and surface properties, makes this class of fluids possible to use in a high plethora of applications [1,2]. Thermophysical properties data, that we can trust, not only because the sam- ples are well purified and characterized, but also because the uncertainty of the data is well discussed, are needed for sev- eral applications and for the design of chemical plants. They can be obtained from experimental measurements, predictive or estimation techniques, and although there were some interest- ing developments in this last area, by using group contribution methods, the calculation of the thermophysical properties of ionic liquids with more or less theoretical based schemes is currently very difficult, but useful for some properties [3]. Exper- 0378-3812/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2010.03.010