US EPA

1468204 

Journal Article 

Ion association in [bmim][PF6]/naphthalene mixtures: an experimental and computational study 

Del Pópolo, MG; Mullan, CL; Holbrey, JD; Hardacre, C; Ballone, P 

2008 

Yes 

Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 

AMER CHEMICAL SOC 

WASHINGTON 

130 

22 

7032-7041 

English 

18461932 

10.1021/ja710841n 

WOS:000256301200038 

https://www.scopus.com/inward/record.uri?eid=2-s2.0-44449174665&doi=10.1021%2fja710841n&partnerID=40&md5=c4fea99e5685ae2852cde9f85f10b5cf
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Mixtures of room temperature ionic liquids (IL) with neutral organic molecules provide a valuable testing ground to investigate the interplay of the ionic and molecular-dipolar state in dense Coulomb systems at near ambient conditions. In the present study, the viscosity eta and the ionic conductivity sigma of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/naphthalene mixtures at T = 80 degrees C have been measured at 10 stoichiometries spanning the composition range from pure naphthalene to pure [bmim][PF6]. The viscosity grows nearly monotonically with increasing IL mole fraction ( x), whereas the conductivity per ion displays a clear peak at x approximately 15%. The origin of this maximum has been investigated using molecular dynamics simulations based on a classical force field. Snapshots of the simulated samples show that the conductivity maximum is due to the gradual transition in the IL component from an ionic state at high x to a dipolar fluid made of neutral ion pairs at low x. At concentrations x < 0.20 the ion pairs condense into molecular-thin filaments bound by dipolar forces and extending in between nanometric droplets of IL. These results are confirmed and complemented by the computation of dynamic and transport properties in [bmim][PF6]/naphthalene mixtures at low IL concentration.