The structure at a molecular level of two ionic liquid homologous series -1-alkyl-3-methylimdazolium hexafluorophosphate and 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide- are probed using Molecular Dynamics simulations. The studied systems include pure ionic liquids with propyl, hexyl, nonyl and dodecyl side chains and also four selected equimolar binary mixtures within each series. The results show that nano-segregation between the polar network of the ionic liquid and its non-polar domains occurs more effectively for longer alkyl side chains and the hexafluophosphate anion. The non-homogeneous character of the alkyl length found in the mixtures is also detrimental for the formation of well-defined and segregated non-polar domains. (C) 2015 Elsevier B.V. All rights reserved.