Self-assembly in the electrical double layer of ionic liquids

Perkin, Susan; Crowhurst, Lorna; Niedermeyer, Heiko; Welton, Tom; Smith, Alexander M.; Gosvami, Nitya Nand

doi:10.1039/c1cc11322d

Cited by 253 publications

(315 citation statements)

References 25 publications

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“…Our results suggest that a long-range, monotonic force may be a general feature of the electric double layers formed by RTILs in contact with macroscopic charged surfaces, whenever surface-bound ion layers are unable to fully compensate surface charges. For mica surfaces, we find this longrange force to be in series with a short-range, nonmonotonic "oscillatory" structural force that is in agreement with the nanoscale surface-induced ion ordering identified in previous work on RTILs (17,(20)(21)(22)(23)(24)(25). Further, we show that the long-range screening behavior of RTILs can be rationalized via a thermally activated population of either free ions or correlated charge domains, reminiscent of the free electron/hole approximation used in semiconductor physics.…”

Section: Significancesupporting

confidence: 67%

“…These studies predict that the electric double layers formed by RTILs should be short-range and exhibit pronounced charge density oscillations, similar to the screening behavior identified in pioneering work on molten KCl (15). Recent theoretical studies emphasize that complex ion ordering in RTILs can intimately depend on the electrochemical potentials of the charged surfaces (5,(17)(18)(19), but these studies have left intact the picture that the electric double layers formed by RTILs should be very short-ranged.Experimentally, the short-range, surface-induced ordering of ions in RTILs has been confirmed with X-ray scattering experiments, atomic force microscopy (AFM) force measurements, and surface forces apparatus (SFA) measurements (17,(20)(21)(22)(23), with these studies highlighting that the ordering of RTIL ions at surfaces exhibits many subtleties. For example, Atkin et al (22) used AFM to demonstrate that gold electrode surfaces immersed Significance Liquid solutions with high concentrations of electrically charged ions are key elements of many energy storage technologies and are prevalent in biology.…”

mentioning

confidence: 72%

“…Experimentally, the short-range, surface-induced ordering of ions in RTILs has been confirmed with X-ray scattering experiments, atomic force microscopy (AFM) force measurements, and surface forces apparatus (SFA) measurements (17,(20)(21)(22)(23), with these studies highlighting that the ordering of RTIL ions at surfaces exhibits many subtleties. For example, Atkin et al (22) used AFM to demonstrate that gold electrode surfaces immersed Significance Liquid solutions with high concentrations of electrically charged ions are key elements of many energy storage technologies and are prevalent in biology.…”

mentioning

confidence: 72%

“…in RTILs can undergo ion-mediated surface reconstructions under externally applied electrochemical potentials. Perkin et al (23) have shown that RTIL ions self-assemble into ordered (smectic-like) bilayers when the cations contain pronounced nonpolar domains. Recent SFA measurements have added to these pictures by demonstrating the presence of a long-range monotonic, exponentially decaying, equilibrium force that extends to distances of up to 35 ionic diameters per surface (24,25).…”

Section: Significancementioning

confidence: 99%

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Long-range electrostatic screening in ionic liquids

Gebbie

Dobbs

Valtiner

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

229

302

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Electrolyte solutions with high concentrations of ions are prevalent in biological systems and energy storage technologies. Nevertheless, the high interaction free energy and long-range nature of electrostatic interactions makes the development of a general conceptual picture of concentrated electrolytes a significant challenge. In this work, we study ionic liquids, single-component liquids composed solely of ions, in an attempt to provide a novel perspective on electrostatic screening in very high concentration (nonideal) electrolytes. We use temperature-dependent surface force measurements to demonstrate that the long-range, exponentially decaying diffuse double-layer forces observed across ionic liquids exhibit a pronounced temperature dependence: Increasing the temperature decreases the measured exponential (Debye) decay length, implying an increase in the thermally driven effective free-ion concentration in the bulk ionic liquids. We use our quantitative results to propose a general model of long-range electrostatic screening in ionic liquids, where thermally activated charge fluctuations, either free ions or correlated domains (quasiparticles), take on the role of ions in traditional dilute electrolyte solutions. This picture represents a crucial step toward resolving several inconsistencies surrounding electrostatic screening and charge transport in ionic liquids that have impeded progress within the interdisciplinary ionic liquids community. More broadly, our work provides a previously unidentified way of envisioning highly concentrated electrolytes, with implications for diverse areas of inquiry, ranging from designing electrochemical devices to rationalizing electrostatic interactions in biological systems.electrostatic interactions | intermolecular interactions | interfacial phenomena | Boltzmann distribution | activation energy E lectrolyte solutions are multicomponent liquids that are composed of ions (solutes) dissolved in a liquid phase (solvent), a classic example being salt water. Like any ideal mixture, the driving force for the dissolution of ions in electrolyte solutions is entropic. Unlike ideal mixtures, the long-range nature and high interaction free energy of the electrostatic interactions between ions ensures that the physical properties of all but the most dilute electrolyte solutions exhibit pronounced deviations from ideal behavior. These deviations primarily arise from the steric "crowding" of ions and the electrostatic correlation of ions, for example the formation of neutral ion pairs, both of which increase the range of electrostatic interactions, compared with ideal solutions (1). As a result, the development of a general conceptual picture of concentrated electrolyte solutions remains challenging. Nevertheless, electrolytes with high ionic concentrations are prevalent in biological systems (2) and technological applications, such as energy storage devices (3-5), so overcoming this challenge remains an important task.In this work, we study room-temperature ionic liquids (RTILs), ...

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Section: Significancesupporting

confidence: 67%

mentioning

confidence: 72%

mentioning

confidence: 72%

Section: Significancementioning

confidence: 99%

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Long-range electrostatic screening in ionic liquids

Gebbie

Dobbs

Valtiner

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

229

302

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“…A rich library of nanostructures were observed both adsorbed onto [33][34][35][36][37] and near 33,36 solid interfaces, which revealed that previous descriptions based on data normal to the IL-solid interface were far too simplistic. [38][39][40][41] The nanostructure of the ion layer in contact with the substrate is strongly affected by the registry between the ions and surface adsorption sites, 13,[33][34][35][36][37] except when the cation is large and sterically hindered. 33 As in the bulk, near surface nanostructure is sensitive to both cation and anion type.…”

Section: Introductionmentioning

confidence: 99%

Near surface properties of mixtures of propylammonium nitrate with n-alkanols 1. Nanostructure

Elbourne

Cronshaw

Voïtchovsky

et al. 2015

Phys. Chem. Chem. Phys.

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. * Corresponding author AbstractIn situ amplitude modulated -atomic force microscopy (AM-AFM) has been used to probe the nanostructure of mixtures of propylammonium nitrate (PAN) with n-alkanols near a mica surface. PAN is a protic ionic liquid (IL) which has a bicontinuous sponge-like nanostructure of polar and apolar domains in the bulk, which becomes flatter near a solid surface. Mixtures of PAN with 1-butanol, 1-octanol, and 1-dodecanol at 10 -70 vol% n-alkanol have been examined, along with each pure n-alkanol, to reveal the effect of composition and n-alkanol chain length. At low concentrations the butanol simply swells the PAN nearsurface nanostructure, but at higher concentrations the nanostructure fragments. Octanol and dodecanol first lower the preferred curvature of the PAN near-surface nanostructure because, unlike n-butanol, their alkyl chains are too long to be accommodated alongside the PAN cations. At higher concentrations, octanol and dodecanol self-assemble into n-alkanol rich aggregates in a PAN rich matrix. The concentration at which aggregation first becomes apparent decreases with n-alkanol chain length.2

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In‐SituScanning Probe Microscopies: Imaging and Beyond

Mao

2014

Developments in Electrochemistry

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Self-assembly in the electrical double layer of ionic liquids

Cited by 253 publications

References 25 publications

Long-range electrostatic screening in ionic liquids

Long-range electrostatic screening in ionic liquids

Near surface properties of mixtures of propylammonium nitrate with n-alkanols 1. Nanostructure

In‐SituScanning Probe Microscopies: Imaging and Beyond

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