Medida de propiedades físicas de líquidos iónicos y de sus mezclas con agua y etanol

Resumo

The aim of this work is to measure experimentally physical properties of ionic liquids and its mixtures with water and ethanol. We choose ionic liquids from two families of the available commercial imidazolium based ones, the 1-alkyl-3-methylimidazolium tetrafluoroborate (CnMIM-BF4) and 1-ethyl-3-methylimidazolium alkyl sulphate (EMIM-CnS), being alkyl group ethyl, butyl, hexyl and octyl in both series of ionic liquids. The CnMIM-BF4 ionic liquids allow us to see the influence of the cation size on physical properties while we can analyze the influence of the alkyl chain length of the anion with the EMIM-CnS ionic liquids. We have done, as well, measurements at different temperature and pressure conditions to see their influence on the physical properties. These ones can also be modulated by mixing them with other solvents, and for this reason, we measured them mixed in the whole range of miscible concentrations, with water and ethanol. The knowledge of these properties is necessary to develop industrial process and to design new ionic liquids for a specific purpose by changing their formulation. In addition, they are essential for the development and checking of theoretical models and numerical simulations. At the beginning of this work the number of published papers on this subject was scarce but a great number of articles have been published in the last years. We present in chapter 2 a bibliography revision of the published papers about the physical properties we measured. Density was measured using three different vibrating tube densimeters from Anton Paar, SVM3000 viscodensimeter, DSA5000 that also measure speed of sound and DMA60/512P for measuring at different pressure conditions. We measured surface tension in a drop volume tensiometer Lauda TVT1. Viscosity data were obtained using a Stabinger Viscometer (Anton Paar SVM3000) and a falling sphere viscometer (Anton Paar AMVn), conductivity by means of a Crison GLP31+ and finally, refractive index data were measured with a refractometer ATAGO RX-1000 as we explain in chapter 3. We plot all measured data on chapter 4 where we can check the influence of the alkyl chain length of both anion and cation in physical properties. From experimental density, surface tension, viscosity and refractive index data we work out, in chapter 5, molar volumes, excess molar volumes, surface tension, viscosity and refractive index deviations respectively, as well as isoentropic compressibility coefficient from speed of sound and density data and isothermal compressibility and isobaric expansion from density data obtained al different pressure conditions (apendix 2). Experimental data were also compared with those previously published, and a good agreement was observed for all the properties. Finally, in chapter 6, surface tension and conductivity data were used to contribute in the development of the Bahe-Varela theory, based on the pseudolattice formalism, for surface tension of aqueous mixtures of ionic liquids, and for charge transport in ionic liquid solution. Also we applied Bahe-Varela theory developed for partial molar volumes of ionic liquids in mixtures to data of the binary systems analyzed in this work, checking that this theory is appropriated to reproduce these experimental data.