Dynamic heterogeneity and viscosity decoupling: origin and analytical prediction

Das, Nilimesh; Sen, Pratik

doi:10.1039/d1cp01804c

Cited by 19 publications

(12 citation statements)

References 56 publications

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“…The apparent decoupling of viscosity from diffusion has been seen before, for both RTIL and deep eutectic solvent (DES) systems. In those works, this decoupling was interpreted as evidence for heterogeneity within the media, and our findings are consistent with that explanation. − In other words, the viscosity sensed by reorientation measurements is that of the environment in the immediate proximity of the chromophore, while bulk viscosity is reflective of interactions between larger assemblies (e.g., aggregates) in which the chromophores are confined.…”

Section: Results and Discussionsupporting

confidence: 89%

Relating the Induced Free Charge Density Gradient in a Room-Temperature Ionic Liquid to Molecular-Scale Organization

et al. 2023

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We report on dilution-dependent changes in the local environments of chromophores incorporated into roomtemperature ionic liquid (RTIL)-molecular solvent binary systems where the ionic liquid cation and molecular solvent possess the same alkyl chain length. We have used the RTIL 1-decyl-1methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (DMPyrr + TFSI − ) and the molecular solvent 1-decanol. Perylene was used as a non-polar probe, and cresyl violet (CV + ) was used as a polar probe chromophore. We observe that in both regions there is a change in the chromophore local environments with increasing 1-decanol content. The changes in the nonpolar regions of the binary RTIL-molecular solvent system occur at a lower 1-decanol concentration than changes in the polar regions. Both chromophores reorient as oblate rotors in this binary system, allowing detailed information on the relative values of the Cartesian components of the rotational diffusion constants to be extracted from the experimental data. The induced free charge density gradient, ρ f , known to exist in RTILs, persists to high 1-decanol content (1decanol mole fraction of 0.75), with the structural details of the gradient being reflected in depth-dependent changes in the Cartesian components of the rotational diffusion constants of CV + . This is the first time that changes in molecular organization have been correlated with ρ f .

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Section: Results and Discussionsupporting

confidence: 89%

Relating the Induced Free Charge Density Gradient in a Room-Temperature Ionic Liquid to Molecular-Scale Organization

et al. 2023

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“…Such a difference could also be viewed as a variation in the frictional term, f , with dilution. There is an interesting body of work that shows the nature of solvent–solute coupling can exhibit heterogeneity in complex systems, 52,53 but we believe that such heterogeneity is not dominant in the systems under consideration because the timescale of environmental exchange that would give rise to such an effect would be necessarily much shorter than the measured rotational diffusion times reported here. In other words, any short-term fluctuations in f would be temporally averaged over the timescale relevant for chromophore rotation.…”

Section: Resultsmentioning

confidence: 68%

The effect of dilution on induced free charge density gradients in room temperature ionic liquids

Hossain

Blanchard

2022

Phys. Chem. Chem. Phys.

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“…This value is an approximate value of many similar fluorophores, − particularly those measured in ILs . It is also possible that solute diffusion–viscosity decoupling contributes to the negative deviation …”

Section: Resultsmentioning

confidence: 85%

“…91 It is also possible that solute diffusion−viscosity decoupling contributes to the negative deviation. 92 For all solvents, the 1 μm films reveal a positive deviation from the Stokes−Einstein relationship; the magnitude of this deviation is larger for [C 6 mim][Cl] and [C 8 mim][Cl] ILs than for glycerol, particularly at higher temperatures. The axial resolution of the FRAP instrument, as defined by Abbe, 93 is approximately 14 μm.…”

Section: ■ Results and Discussionmentioning

confidence: 89%

Temperature-Dependent Constrained Diffusion of Micro-Confined Alkylimidazolium Chloride Ionic Liquids

et al. 2022

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Alkylimidazolium chloride ionic liquids (ILs) have many uses in a variety of separation systems, including micro-confined separation systems. To understand the separation mechanism in these systems, the diffusion properties of analytes in ILs under relevant operating conditions, including micro-confinement dimension and temperature, should be known. For example, separation efficiencies for various IL-based microextraction techniques are dependent on the sample volume and temperature. Temperature-dependent (20–100 °C) fluorescence recovery after photobleaching (FRAP) was utilized to determine the diffusion properties of a zwitterionic, hydrophilic dye, ATTO 647, in alkylimidazolium chloride ILs in micro-confined geometries. These micro-confined geometries were generated by sandwiching the IL between glass substrates that were separated by ∼1 to 100 μm. From the measured temperature-dependent FRAP data, we note alkyl chain length-, thickness-, and temperature-dependent diffusion coefficients, with values ranging from 0.021 to 46 μm2/s. Deviations from Brownian diffusion are observed at lower temperatures and increasingly less so at elevated temperatures; the differences are attributed to alterations in intermolecular interactions that reduce temperature-dependent nanoscale structural heterogeneities. The temperature- and thickness-dependent data provide a useful foundation for efficient design of micro-confined IL separation systems.

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Dynamic heterogeneity and viscosity decoupling: origin and analytical prediction

Abstract: Molecular-level structure and dynamics decide the functionality of a solvent media. Therefore, a significant amount of effort was dedicated, being dedicated, and will be dedicated in understanding its structural and...

Cited by 19 publications

References 56 publications

Relating the Induced Free Charge Density Gradient in a Room-Temperature Ionic Liquid to Molecular-Scale Organization

Relating the Induced Free Charge Density Gradient in a Room-Temperature Ionic Liquid to Molecular-Scale Organization

The effect of dilution on induced free charge density gradients in room temperature ionic liquids

Temperature-Dependent Constrained Diffusion of Micro-Confined Alkylimidazolium Chloride Ionic Liquids

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