1,721,043 research outputs found
Dielectric spectroscopy experimental study on the relaxation process in ionic liquids/moleculare liquids mixtures
No full textRunning dielectric spectroscopy measurements on the relaxation processes in fluorinated ionic liquids
No full textNew experimental evidence supporting the mesoscopic segregation model in room temperature ionic liquids
No full textThe existence of a high degree of order over the mesoscopic spatial scale in room temperature ionic liquids is one of their most intriguing properties. Recently the possibility that such a feature, that is witnessed by the occurrence of peculiar low Q diffraction features, reflects nm-scale structural organization has been questioned on the basis of both experimental and computational studies. In this contribution we discuss these studies and present novel experimental evidence that confirm the existence of nm-scale spatial heterogeneities due to the segregation of apolar moieties dispersed in a polar network. The consequence of this scenario is that when the chain polarity gets closer to that of the charged head, the structural heterogeneities are no longer observed
Comparing intermediate range order for alkyl- vs. ether-substituted cations in ionic liquids
No full textX-ray scattering data from four pairs of ionic liquids (ILs) are compared. The alkyl-substituted cations show a first sharp diffraction peak between 3 and 4 nm(-1) that is not observed for ILs having cations with ether- or hydroxy-substitutions. These observations indicate a significant difference in the intermediate range order for these liquids
Micro- and mesoscopic structural features of a bio-based choline-amino acid ionic liquid
No full textHigh energy X-ray diffraction data from a bio-based ionic liquid constituted by choline ([cho]) and an amino acid (AA), namely n-leucine ([nle]), are presented and described by means of an atomistic molecular dynamics simulation aiming at extracting detailed structural information at both microscopic and mesoscopic spatial scales. We find that similar to other previously studied analogous systems, a strong, hydrogen bonding driven, cation–anion correlation determines the microscopic structure. While other peculiar correlations exist in this [cho][nle] IL, the medium length alkyl tail of the AA leads to the development of a characteristic polar vs. apolar alternation, as a consequence of the alkyl tails segregation into domains, thus delivering the formation of an enhanced level of mesoscopic organization in this IL
Complexity of structural and dynamic features in RTILs
No full textRoom temperature ionic liquids (RTILs) are characterised by the coexistence of polar and apolar moieties. The different nature of the interaction between these moieties leads to a complex morphology, as the apolar part (typically represented by alkyl chains) tend to segregate into nm-scale clusters that are embedded into a three-dimensional charged (polar) network.
Such a behaviour was originally proposed in the basis of molecular dynamics simulations and confirmed on the basis of experimental data.
We will report on X-ray and neutron diffraction experiments highlighting the existence of nano-scale structural heterogeneities in a variety of RTILs.
Furthermore, we will show that this complex morphology has strong implications on the relaxation dynamics in these systems. Using Neutron Spin Echo, dielectric and mechanical spectroscopies we will highlight the existence of relaxation processes whose activation energy depends upon the size of the structural heterogeneities
Heterogeneous large amplitude atomic motion in supercooled liquids
No full textOne of the central questions in glass physics is the dynamic nature of the glass transition. Essential issues are the type of atomic motions involved and their homogeneity or heterogeneity. Previous experimental studies of the dynamic heterogeneity performed by special NMR techniques for times > 10 -6 s and by incoherent neutron scattering were restricted to the α-relaxation process. Here we review the results of neutron scattering studies focused on the picosecond time domain showing that fast β-process corresponds to large amplitude cluster like heterogeneous motion. © 2003 Published by Elsevier Science B.V
Mesoscopic organization in ionic liquids: structural and dynamic implications.
No full textRoom temperature ionic liquids are an exciting novel class of materials1 that are composed solely of ionic species; nevertheless, due to their asymmetric chemical structure (see the figure), they show a low (<100°C) melting point. They show negligible vapor pressure and a wide tunability of the chemical-physical properties upon slight changes of the chemical details (e.g. anion and cation nature).
One of the most striking features emerging among the properties of these materials is the existence of high degree of structural heterogeneity over the nm spatial scale.
Small-Angle X-ray Scattering (SAXS) patterns have been collected on a series of ILs that are characterized by a varying alkyl chain length2. Remarkably, these materials are characterized by a low Q amorphous, whose amplitude as well as position depends on the chain length. These findings have been rationalized in terms of a nanoscale segregated morphology, where the alkyl chains self-assemble into domains embedded into the charged matrix.
Such a structural scenario can be expected to play a role in the relaxation dynamics in ILs. We collected Neutron Spin Echo measurements on a series of deuterated ILs, in order to access specific information on the collective dynamics in these salts3. These experiments highlighted evidences of deviations from the commonly observed viscosity-driven collective dynamics.
1. E. W. Castner et al., J. Chem. Phys., 2010, 132, 120901; J. Wishart, J. Phys. Chem. Lett., 2010, 1, 1629
2. A. Triolo et al., J. Phys. Chem. B, 2007, 111, 4641; Chem. Phys. Lett., 2008, 457, 362; J. Chem. Phys., 2009, 130, 164521
3. A. Triolo et al., J. Phys. Chem. B, 2009, 113, 846
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