  The work reports transport and structure properties of the three
pyridinium-based ionic liquids (RTILs) - N-butylpyridinium hexafluorophosphate
[BPY][PF6], N-butylpyridinium trifluorosulfonate [BPY][TF] and
N-butylpyridinium bis(trifluoromethanesulfonyl)imide [BPY][TFSI] - in their
mixtures with acetone (ACET). The ionic conductivity maximum occurs at 10 mol%
RTIL, irrespective of the anion. The absolute ionic conductivity value of
[BPY][TF] is higher than those of other RTILs. This is explained by a weaker
cation-anion binding than that in [BPY][PF6] and smaller anion size than that
of [BPY][TFSI]. All the investigated RTILs are infinitely miscible with ACET,
which boosts their diffusivity and conductivity. A small viscosity of ACET
favors a drastic viscosity decay in the RTIL-ACET mixtures. Structure analysis
(radial distribution functions, ionic clusters) of the mixtures are in line
with their transport properties providing a reliable microscopic interpretation
of the observed macroscopic properties. As a molecular co-solvent, ACET
constitutes an interesting alternative and competitor to more intensively
investigated liquids.
