The objective of this thesis is to broaden the knowledge of thermophysical and thermodynamic properties of ionic liquids and their mixtures with other fluids. Seven ionic liquids were chosen - 1-butyl-3-methylimidazolium tetrafluroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide, trimethyl-butylammonium bis(trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium ethylsulfate and butyl-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide - in order to assess the influence of both the cations and anions on the measured properties. The first part of this work consisted of the study of thermophysical properties (density and viscosity) of ionic liquids and their mixtures with water, as a function of temperature between 293K and 423K and the composition at atmospheric pressure. The study of the densities of pure ionic liquids was carried out at different pressures, up to 40 MPa, which allowed determination of their mechanical coefficients. The second part of the study concentrated on the fluid phase equilibrium between an ionic liquid and another fluid. First, the solubility of eight gases - carbon dioxide, ethane, methane, nitrogen, oxygen, argon, hydrogen and carbon monoxide - in ionic liquids was studied between 283K and 343K ; at pressures close to atmospheric. Finally, the miscibility of ionic liquids with water and three alcohols - 1-hexanol, hexan-1,2-diol and cyclohexanol - was determined at different temperatures.
