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Structural heterogenities over nanometer scale in room temperature ionic liquids

Room temperature ionic liquids represent a novel class of materials that is attracting a great applicative interest due to their negligible vapour pressure and tunability of physical-chemical properties. They are typically built up by a bulk, asymmetric cation, bearing a side alkyl chain and a fluorinated anion. The charge delocalization hinders the crystallization, thus leading to a wide stability range for the liquid phase. As a consequence of the amorphous nature of the liquid state of these materials, their morphology should be characterised by a limited degree of order over short to medium spatial scales, due to repulsive, dispersive and coulombic interactions.
Using X-ray diffraction techniques, we highlighted that these materials are characterised by a high degree of long range order of a spatial scale of nanometers.
The proposed structural model considers that the charged portions of the material organise themselves in a structure that is mainly determined by the strong coulombic interactions. On the other hand, the alkyl chains (that are strongly apolar) tend to segregated, leading to the formation of nano-scale domains. The morphology is then characterised by oily nano-pools that are embedded into a charged three-dimensional matrix.
Such a structural model implies a nano-structuring due to self-assembly and turns out to be adequate to rationalising many peculiar properties of these materials, such as the anomalous viscosity dependence from the alkyl chain length.
This peculiar mesoscopic morphology can be exploited for many applications ranging from chemical separation to nanoparticle synthesis and catalysis.
The results of this study have been published: "Nanoscale Segregation in Room Temperature Ionic Liquids" Journal of Physical Chemistry 118 (2007) 4641 (A. Triolo, O. Russina, H.-J. Bleif, E. Di Cola). Confirming the importance of these findings, the paper has been considered as 'Most Cited JPCB Paper' among the ones published in 2007 and 'Hot Paper' in march 2008 (Source: Web of Science, ISI).