355 results found
Kornyshev A, Sikdar D, Weir H, Optical response of electro-tuneable 3D superstructures of plasmonic nanoparticles self-assembling on transparent columnar electrodes, Optics Express, ISSN: 1094-4087
Electrically tuneable, guided self-assembly of plasmonic nanoparticles (NPs) at polarized, patterned solid–liquid interfaces could enable numerous platforms for designing nanoplasmonic optical devices with new tuneable functionalities. Here, we propose a unique design of voltage-controlled guided 3D self-assembly of plasmonic NPs on transparent electrodes, patterned as columnar structures — arrays of vertical nanorods. NP assembly on the electrified surfaces of those columnar structures allows formation of a 3D superstructure of NPs, comprising stacking up of NPs in the voids between the columns, forming multiple NP-layers. A comprehensive theoretical model, based on quasi-static effective medium theory and multilayer Fresnel reflection scheme, is developed and verified against full-wave simulations for obtaining optical responses — reflectance, transmittance, and absorbance — from such systems of 3D self-assembled NPs. With a specific example of small gold nanospheres, self-assembling on polarized zinc oxide columns, we show that the reflectance spectrum can be controlled by the number of stacked NP-layers. Numerical simulations show that peak reflectance can be enhanced up to ~1.7 times, along with spectral broadening by a factor of ~2 — allowing wide range tuning of optical reflectivity. Smaller NPs with superior mobility would be preferable over large NPs for realizing such devices for novel photonic and sensing applications.
Kondrat S, Vasilyev OA, Kornyshev AA, 2019, Feeling your neighbors across the walls: How interpore ionic interactions affect capacitive energy storage., Journal of Physical Chemistry Letters, Vol: 10, Pages: 4523-4527, ISSN: 1948-7185
Progress in low-dimensional carbon materials has intensified research on supercapacitors with nanostructured/nanoporous electrodes. The theoretical and simulation work so far has focused on charging single nanopores or nanoporous networks and the effects due to ionic interactions inside the pores, while the effect of interpore ion-ion correlations has received less attention. Herein, we study how the interactions between the ions in the neighboring pores across the pore walls affect capacitive energy storage. We develop a simple lattice model for the ions in a stack of parallel-aligned nanotubes, solve it by using the perturbation and "semi-mean-field" theories, and test the results by Monte Carlo simulations. We demonstrate that the interpore ionic interactions can have a profound effect on charge storage; in particular, such interactions can enhance or diminish the stored energy density, depending on the sign of like-charge interactions. We also find that charging can proceed either continuously or via a phase transition. Our results call for more detailed investigations of the properties of carbon pore walls and suggest that tuning their electrostatic response may be promising for the rational design of an optimal supercapacitor.
Ma Y, Sikdar D, Fedosyuk A, et al., 2019, An auxetic thermo-responsive nanoplasmonic optical switch., ACS Applied Materials and Interfaces, ISSN: 1944-8244
Development and use of metamaterials have been gaining prominence in large part due to the possibility of creating platforms with 'disruptive' and unique optical properties. However, to date the majority of such systems produced using micro or nanotechnology, are static and can only perform certain target functions. Next-generation multifunctional smart optical metamaterials are expected to have tuneable elements with the possibility of controlling the optical properties in real time via variation in parameters such as pressure, mechanical stress, voltage, or through non-linear optical effects. Here, we address this challenge by developing a thermally controlled optical switch, based on the self-assembly of poly(N-isopropylacrylamide)-functionalised gold nanoparticles on a planar macroscale gold substrate. We show that such meta-surfaces can be tuned to exhibit substantial changes in the optical properties both in terms of wavelength and intensity, through the temperature-controlled variation of the interparticle distance within the nanoparticle monolayer as well as its separation from the substrate. This change is based on temperature induced auxetic expansion and contraction of the functional ligands. Such a system has potential for numerous applications, ranging from thermal sensors to regulated light harnessing.
Montelongo Y, Sikdar D, Ma Y, et al., 2019, Author Correction: Electrotunable nanoplasmonic liquid mirror., Nat Mater, ISSN: 1476-1122
In the version of this Article originally published, the last sentence of the acknowledgements incorrectly read 'L.V. acknowledges the support of a Marie Skodowska-Curie fellowship (N-SHEAD)'; it should have read 'L.V. and D.S. acknowledge the support of Marie Skłodowska-Curie fellowships, N-SHEAD and S-OMMs, respectively'.
Feng G, Kornyshev A, Goodwin Z, 2019, Free and bound states of ions in ionic liquids, conductivity, and underscreening paradox, Physical Review X, Vol: 9, ISSN: 2160-3308
Free and Bound States of Ions in Ionic Liquids, Conductivity, and Underscreening ParadoxGuang Feng,1,* Ming Chen,1 Sheng Bi,1 Zachary A.H. Goodwin,2,3 Eugene B. Postnikov,4 Nikolai Brilliantov,5,6* Michael Urbakh,7,* and Alexei A. Kornyshev3,8*1State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Room 321, Power Building, 1037 Luoyu Road, Wuhan, Hubei 430074 China2Department of Physics, Imperial College London, South Kensington Campus, SW7 2AZ London, United Kingdom3Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, White City Campus, W12 0BZ London, United Kingdom4Theoretical Physics Department, Kursk State University, Radishcheva Str., 33, Kursk 305000, Russia5Department of Mathematics, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom6Skolkovo Institute of Science and Technology, Moscow 121205, Russia7School of Chemistry, The Sackler Faculty of Science, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel8Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, South Kensington Campus, SW7 2AZ London, United Kingdom*Correspondence: firstname.lastname@example.org (GF), email@example.com (MU), firstname.lastname@example.org (NB) and email@example.com (AAK) ABSTRACTUsing molecular dynamics simulations and theoretical analysis of velocity autocorrelation functions, we study ion transport mechanisms in typical room temperature ionic liquids. We show that ions may reside in two states – free and bound with an inter-state exchange; we investigate quantitatively the exchange process and reveal new qualitative features of this process. To this end we propose a dynamic criterion for free and bound ions, based on the ion trajectory density and demonstrate that this criterion is consistent with a static one, based on interionic distances. Analyzing the trajectories of individual cations and anions, we estimate t
Sikdar D, Ma Y, Kucernak AR, et al., 2019, Nanoplasmonic Metamaterial Devices as Electrically Switchable Perfect Mirrors and Perfect Absorbers
© 2019 The Author(s) 2019 OSA. We introduce nanoplasmonic metamaterial devices - electrically-switchable between perfect-mirror/absorber states - based on voltage-controlled assembly/disassembly of gold nanoparticles on silver films. These are investigated using effective-medium-theory, verified with simulations and experiments.
Sikdar D, Ma Y, Kucernak AR, et al., 2019, Nanoplasmonic Metamaterial Devices as Electrically Switchable Perfect Mirrors and Perfect Absorbers, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Bi S, Wang R, Liu S, et al., 2018, Minimizing the electrosorption of water from humid ionic liquids on electrodes, Nature Communications, Vol: 9, ISSN: 2041-1723
In supercapacitors based on ionic liquid electrolytes, small amounts of absorbed water could potentially reduce the electrochemical window of electrolytes and cause performance degradation. The same would take place if ionic liquids are used as solvents for electrocatalysis involving the dissolved molecular species. In this work, we carry out molecular dynamics simulations, with gold and carbon electrodes in typical ionic liquids, hydrophobic and hydrophilic, to study electrosorption of water. We investigate the effects of hydrophobicity/hydrophilicity of ionic liquids and electrodes on interfacial distribution of ions and electrosorbed water. Results reveal that using hydrophilic ionic liquids would help to keep water molecules away from the negatively charged electrodes, even at large electrode polarizations. This conclusion is supported by electrochemical cyclic voltammetry measurements on gold and carbon electrodes in contact with humid ionic liquids. Thereby, our findings suggest potential mechanisms for protection of electrodes from water electrosorption.
Ma Y, Zagar C, Klemme DJ, et al., 2018, A tunable nanoplasmonic mirror at an electrochemical interface, ACS Photonics, Vol: 5, Pages: 4604-4616, ISSN: 2330-4022
Designing tunable optical metamaterials is one of the great challenges in photonics. Strategies for reversible tuning of nanoengineered devices are currently being sought through electromagnetic or piezo effects. For example, bottom-up self-assembly of nanoparticles at solid | liquid or liquid | liquid interfaces can be used to tune optical responses by varying their structure either chemically or through applied voltage. Here, we report on a fully reversible tunable-color mirror based on a TiN-coated Ag substrate immersed in an aqueous solution of negatively charged Au-nanoparticles (NPs). Switching electrode potential can be used to fully control the assembly/disassembly of NPs at the electrode | electrolyte interface within a 0.6 V wide electrochemical window. The plasmon coupling between the electrode and the adsorbed NP array at high positive potentials produces a dip in the optical reflectance spectrum, creating the "absorber" state. Desorption of NPs at low potentials eliminates the dip, returning the system to the reflective "mirror" state. The intensity and wavelength of the dip can be finely tuned through electrode-potential and electrolyte concentration. The excellent match between the experimental data and the theory of optical response for such system allows us to extract valuable information on equilibrium and kinetic properties of NP-assembly/disassembly. Together with modeling of the latter, this study promotes optimization of such meta-surfaces for building electrotunable reflector devices.
Bresme F, Robotham O, Chio W-IK, et al., 2018, Debye screening, overscreening and specific adsorption in solutions of organic ions, Physical Chemistry Chemical Physics, Vol: 20, Pages: 27684-27693, ISSN: 1463-9076
Tetrabutylammonium (TBA) and tetraphenylborate (TPB) ions dissolved in dichloroethane (DCE) are widely used in electrochemistry of liquid–liquid interfaces. Unlike alkali halide solutions in water, TBA–TPB–DCE solutions feature large organic ions and a solvent with a dielectric constant almost one order of magnitude lower than that of water. This is expected to dramatically amplify the impact of ionic correlations in the properties of the solution. Here we report atomistic simulations of TBA–TPB–DCE solutions and analyze ion correlations, clustering, and charge screening effects. We target concentrations in the range of 0.01–0.25 molal (m), hence exploring concentration regimes typical for many experimental investigations. We show that the transition from monotonic to oscillatory decay of the charge density, which signals the onset of strong ion correlations, takes place in this concentration interval, leading to overscreening effects. Furthermore, we investigate the distribution and adsorption of ions at the DCE–air interface. Unlike what is observed for small inorganic ions in water at similar concentrations, we find that TPB and TBA ions accumulate near the DCE surface, resulting in significant interfacial clustering and adsorption at concentrations ∼0.25 m. TPB ions adsorb more strongly leading to free energy wells of ∼1–2 kBT. The adsorption modifies significantly the electrostatic potential of the DCE–air interface, which undergoes a shift of 0.2 V in going from pure DCE to TBA–TPB–DCE solutions at 0.25 m.
Goodwin ZAH, Kornyshev AA, 2018, Theory of polymer-electrolyte-composite electroactuator sensors with flat or volume-filling electrodes, Soft Matter, Vol: 14, Pages: 7996-8005, ISSN: 1744-683X
In reverse actuation, a voltage/electrical-current signal can be generated from applying a mechanical force to an electroactuator. Such processes are of interest in touch sensing and soft robotics applications. We develop a classical density functional theory of reverse actuation for polymer-electrolyte-composite electroactuators, which treats mobile cations in the same spirit as forward actuation (curving in response to applied voltage). The proposed framework is applied to electroactuators with micro-structured porous electrodes (with cylindrical or slit pores) and flat electrodes, the dynamic response of which has to be modelled differently. Open- and short-circuit operation modes are investigated separately. A detailed analysis of the proposed theory indicates the preferred architectures for sensing, depending on the operation regimes.
McEldrew M, Goodwin ZAH, Kornyshev AA, et al., 2018, Theory of the Double Layer in Water-in-Salt Electrolytes., Journal of Physical Chemistry Letters, Vol: 9, Pages: 5840-5846, ISSN: 1948-7185
One challenge in developing the next generation of lithium-ion batteries is the replacement of organic electrolytes, which are flammable and most often contain toxic and thermally unstable lithium salts, with safer, environmentally friendly alternatives. Recently developed water-in-salt electrolytes (WiSEs), which are nonflammable, nontoxic, and also have enhanced electrochemical stability, are promising alternatives. In this work, we develop a simple modified Poisson-Fermi theory for WiSEs, which demonstrates the fine interplay between electrosorption, solvation, and ion correlations. The phenomenological parameters are extracted from molecular dynamics simulations, also performed here. The theory reproduces the WiSEs' electrical double-layer structure with remarkable accuracy.
Budkov YA, Kolesnikov AL, Goodwin ZAH, et al., 2018, Theory of electrosorption of water from ionic liquids, Electrochimica Acta, Vol: 284, Pages: 346-354, ISSN: 0013-4686
We propose and develop a classical density functional theory for the description of a minor amount of water dissolved in ionic liquid in the vicinity of an electrode. In addition to the electrostatic energy and lattice-gas mixing entropy terms, the utilised grand canonical potential contains several phenomenological terms/parameters that describe short-range interactions between ions, water molecules and the electrode. Here we investigate: (i) specific interaction of ions and molecules with the electrode, which are responsible for their specific adsorption; (ii) hydrophilicity/hydrophobicity of ions. We obtain water electrosorption isotherms as a function of the potential drop across the electrical double layer, investigate its asymmetry with respect to the sign of electrode potential, and establish the relationship between the sign of this asymmetry and hydrophobicity/hydrophilicity of cations and anions. We also calculate the effect of water electrosorption on the double layer differential capacitance which brings clear new features to its voltage dependence, some of which have been already experimentally observed.
Goodwin Z, Eikerling M, Loewen H, et al., 2018, Theory of microstructured polymer-electrolyte artificial muscles, Smart Materials and Structures, Vol: 27, ISSN: 0964-1726
Ionic electroactuator beams are promising systems for artificial muscles in microrobotics. Here a theory is developed to investigate one promising class of such systems, which employs flexible volume-filling electrodes impregnated with polymer–electrolyte. The theory provides analytical formulae for the equilibrium beam curvature as a function of voltage and structure-related operational parameters. It predicts a possible enhancement of beam curvature by orders of magnitude over that of flat electrodes. Volume-filling electrodes thus constitute one of the 'strongest' architectures for voltage-induced movement. Approximate expressions for the dynamics of tandem pore charging and beam deflection are developed to determine the maximum pore length that still warrants a sufficiently fast response time (up to 1 s). Upper bounds on applied voltage and response time constrain the maximal device thickness and curvature, and therefore, the resulting work such a device can perform.
Pivnic K, Fajardo OY, Bresme F, et al., 2018, Mechanisms of Electrotunable Friction in Friction Force Microscopy Experiments with Ionic Liquids, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 122, Pages: 5004-5012, ISSN: 1932-7447
Using molecular dynamics simulations and a coarse-grained model of ionic liquids (ILs), we study mechanisms of electrotunable friction measured in friction force microscopy experiments, where only one layer of IL is present between the tip and the electrode (substrate). We show that the variation of the friction force with the electrode surface charge density is determined by the regime of motion of the confined IL relative to the substrate and tip. The latter depends on the strengths of the ion–substrate and ion–tip interactions and on the commensurability between the characteristic ion dimensions and lattice spacings of the substrate and tip surfaces. Related with those factors, our simulations predict two strictly different scenarios for the variation of the friction force with the electrode surface charge. Revealing mechanisms of frictional energy dissipation in nanoscale IL films offers a way for controlling friction by tuning ion–substrate interactions and electrical polarization of sliding surfaces.
Kornyshev AA, Sikdar D, Edel JB, et al., 2018, Towards Electrotuneable Nanoplasmonic Fabry–Perot Interferometer, Scientific Reports, Vol: 8, ISSN: 2045-2322
Directed voltage-controlled assembly and disassembly of plasmonic nanoparticles (NPs) at electrified solid–electrolyte interfaces (SEI) offer novel opportunities for the creation of tuneable optical devices. We apply this concept to propose a fast electrotuneable, NP-based Fabry–Perot (FP) interferometer, comprising two parallel transparent electrodes in aqueous electrolyte, which form the polarizable SEI for directed assembly–disassembly of negatively charged NPs. An FP cavity between two reflective NP-monolayers assembled at such interfaces can be formed or deconstructed under positive or negative polarization of the electrodes, respectively. The inter-NP spacing may be tuned via applied potential. Since the intensity, wavelength, and linewidth of the reflectivity peak depend on the NP packing density, the transmission spectrum of the system can thus be varied. A detailed theoretical model of the system’s optical response is presented, which shows excellent agreement with full-wave simulations. The tuning of the peak transmission wavelength and linewidth is investigated in detail. Design guidelines for such NP-based FP systems are established, where transmission characteristics can be electrotuned in-situ, without mechanically altering the cavity length.
Chen M, Goodwin ZAH, Feng G, et al., 2017, On the temperature dependence of the double layer capacitance of ionic liquids., Journal of Electroanalytical Chemistry, Vol: 819, Pages: 347-358, ISSN: 1572-6657
The temperature dependence of room temperature ionic liquids differential capacitance is studied here with both theoretical and computational methods. On the theory front, the lattice-gas mean-field theory of ionic liquids is further generalised to account for ‘ion pairing’ and ‘neutral aggregate’ formation. An anomalous temperature dependence of linear response capacitance was found, similar to that reported in earlier work. The theory also predicted that differential capacitance curves transform from a camel to bell shape with increasing temperature. Molecular dynamics simulations verified the expected transition in shape of differential capacitance curves with temperature and the dependence of linear response capacitance on temperature. Further investigation into charge density distributions revealed an ordered structure, reminiscent of oriented ion pairs and neutral aggregates, extending far enough from the electrode to control the capacitance-voltage response. It was found that these structures were dismantled with increasing temperature, as predicted by the mean-field theory.
Rochester C, Sartor A, Pruessner G, et al., 2017, "One dimensional" double layer. The effect of size asymmetry of cations and anions on charge-storage in ultranarrow nanopores-an Ising model theory, RUSSIAN JOURNAL OF ELECTROCHEMISTRY, Vol: 53, Pages: 1165-1170, ISSN: 1023-1935
We develop a statistical mechanical theory of charge storage in quasi-single-file ionophilic nanopores with pure room temperature ionic liquid cations and anions of different size. The theory is mapped to an extension of the Ising model exploited earlier for the case of cations and anions of the same size. We calculate the differential capacitance and the stored energy density per unit surface area of the pore. Both show asymmetry in the dependence on electrode potential with respect to the potential of zero charge, related to the difference in the size of the ions, which will be interesting to investigate experimentally. It also approves the increase of charge storage capacity via obstructed charging, which in these systems emerges for charging nanopores with smaller ions.
Recently, there has been a drive to design and develop fully tunable metamaterials for applications ranging from new classes of sensors to superlenses among others. Although advances have been made, tuning and modulating the optical properties in real time remains a challenge. We report on the first realization of a reversible electrotunable liquid mirror based on voltage-controlled self-assembly/disassembly of 16 nm plasmonic nanoparticles at the interface between two immiscible electrolyte solutions. We show that optical properties such as reflectivity and spectral position of the absorption band can be varied in situ within ±0.5 V. This observed effect is in excellent agreement with theoretical calculations corresponding to the change in average interparticle spacing. This electrochemical fully tunable nanoplasmonic platform can be switched from a highly reflective ‘mirror’ to a transmissive ‘window’ and back again. This study opens a route towards realization of such platforms in future micro/nanoscale electrochemical cells, enabling the creation of tunable plasmonic metamaterials.
Kolomeisky A, Kornyshev A, 2017, Current-generating double layer shoe with a porous sole, 254th National Meeting and Exposition of the American-Chemical-Society (ACS) on Chemistry's Impact on the Global Economy, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Goodwin ZAH, Kornyshev AA, 2017, Underscreening, overscreening and double-layer capacitance, ELECTROCHEMISTRY COMMUNICATIONS, Vol: 82, Pages: 129-133, ISSN: 1388-2481
There have recently been reports of extraordinarily long screening lengths in concentrated electrolytes and which vary non-monotonically with ion concentration. There were several attempts to explain these puzzling observations. In this communication we further explore possibilities to rationalise those results. Our analysis does not yet close the problem, but it highlights conflicting consequences of the models designed to reproduce those observations.
Bazant M, Bennewitz R, Booth S, et al., 2017, Electrovariable nanoplasmonics: general discussion, FARADAY DISCUSSIONS, Vol: 199, Pages: 603-613, ISSN: 1359-6640
Bazant M, Bennewitz R, Bocquet L, et al., 2017, Electrotunable wetting, and micro- and nanofluidics: general discussion, Publisher: ROYAL SOC CHEMISTRY
Velleman L, Scarabelli L, Sikdar D, et al., 2017, Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation, Faraday Discussions, Vol: 205, Pages: 67-83, ISSN: 1364-5498
Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials and for sensing and optical applications. NPs can spontaneously assemble at the liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening between NPs with the addition of electrolyte or pH adjustment. The in situ modulation of nanoparticle positioning on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision.
To a greater or lesser extent, most room-temperature ionic liquids (RTILs) absorb water from humid air. Penetration of water into the lubricating nanoscale film may affect its equilibrium structure and dynamic properties and thus influence the ability of RTILs as lubricants to reduce friction between solid surfaces. Here we investigate the impact of hydration on lubrication using nonequilibrium molecular dynamics simulations. Water adsorption changes both the ionic liquid molecules’ orientation and the slip conditions at the solid–liquid interfaces, resulting in a reduced resistance against squeezing-out of the lubricant by an external load. For the same normal load, the film becomes thinner when water is present. We show that even small amounts of water can screen the electrostatic interactions between the ions, making RTILs more “fluid” and compressible and hence less resistant to external stress. The impact that screening has on friction involves several aspects that are systematically analyzed in this paper.
Kornyshev AA, Twidale RM, Kolomeisky AB, 2017, Current-Generating Double-Layer Shoe with a Porous Sole: Ion Transport Matters, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 121, Pages: 7584-7595, ISSN: 1932-7447
Generating electrical current from mechanically forced variation of the contact area of electrode/electrolyte interface underpins one of the scenarios of harvesting electrical current from walking. We develop here theory of an electrical shoe with a porous sole with an account of both convection of the liquid electrolyte under pressure and ion migration with transmission-line-type charging of electrical double layer at the pore walls. We show here that ion transport limitations can dramatically reduce the generated current and power density. The developed theory describes the time dependence of the generated current and reveals its dependence on the main operation parameters, the amplitudes of oscillating pressure and frequency, in relation to the system parameters.
Kornyshev AA, Lee DJ, Wynveen A, 2017, Theory of phase segregation in DNA assemblies containing two different base pair sequence types, New Journal of Physics, Vol: 19, ISSN: 1367-2630
Spontaneous pairing ofhomologous DNAsequences –a challenging subject in molecular biophysics,often referred to as‘homology recognition’ –hasbeen observedin vitrofor several DNAsystemsa. One of these experiments involvedliquid crystalline quasi-columnar phases formed by a mixture of two kindsof oligomerof double stranded DNA. Both oligomer types wereof the same length and identical stoichiometric base-pair composition,but the base-pairs followed a different order. Phase segregation of the two DNA types was observedin the experiments, with the formation of boundariesbetween domainsrich inmolecules of one type (order) ofbase pair sequence. We formulate here a modified ‘X-Y model’for phase segregation in such assemblies, obtain approximate solutions of the model, compare analytical results toMonte Carlosimulations, and rationalize pastexperimental observations. This study,furthermore,reveals the factors that affect the degree of segregation. Such information could be usedin planning new versions of similarsegregationexperiments, neededfordeepeningour understanding offorces that might be involved, e.g., ingene-gene recognition.
David A, Fajardo OY, Kornyshev AA, et al., 2017, Electrotunable lubricity with ionic liquids: the influence of nanoscale roughness, Faraday Discuss, Vol: 199, Pages: 279-297, ISSN: 1359-6640
The properties of ionic liquids can be modified by applying an external electrostatic potential, providing a route to control their performance in nanolubrication applications. Most computational studies to date have focused on the investigation of smooth surfaces. Real surfaces are generally inhomogeneous and feature roughness of different length scales. We report here a study of the possible effects that surface roughness may have on electrotunable lubricity with ionic liquids, performed here by means of non-equilibrium molecular dynamics simulations. In order to advance our understanding of the interplay of friction and substrate structure we investigate coarse grained models of ionic liquids confined in model surfaces with nanometer roughness. The friction is shown to depend on the roughness of the substrate and the direction of shear. For the investigated systems, the friction coefficient is found to increase with roughness. These results are in contrast with previous studies, where roughness induced reduction of friction was reported, and they highlight the strong sensitivity of the friction process to the structure of the surfaces. The friction force features a maximum at a specific surface charge density. This behaviour is reminiscent of the one reported in ionic liquids confined by flat surfaces, showing the generality of this physical effect in confined ionic liquids. We find that an increase of the substrate-liquid dispersion interactions shifts the maximum to lower surface charges. This effect opens a route to control electrotunable friction phenomena by tuning both the electrostatic potential and the composition of the confining surfaces.
Goodwin ZAH, Feng G, Kornyshev AA, 2016, Mean-field theory of electrical double layer in ionic liquids with account of short-range correlations, Electrochimica Acta, Vol: 225, Pages: 190-197, ISSN: 0013-4686
We develop the theory of the electrical double layer in ionic liquids as proposed earlier by Kornyshev (2007). In the free energy function we keep the so called ‘short-range correlation terms’ which were omitted there. With some simplifying assumptions, we arrive at a modified expression for differential capacitance, which makes differential capacitance curves less sharply depending on electrode potential and having smaller values at extrema than in the previous theory. This brings the results closer to typical experimental observations, and makes it appealing to use this formalism for treatment of experimental data. Implications on Debye length and the extent of ion paring in ionic liquids are then briefly discussed.
Sikdar D, Bucher A, Zagar C, et al., 2016, Electrochemical plasmonic metamaterials: towards fast electro-tuneable reflecting nanoshutters, Faraday Discuss, Vol: 199, Pages: 585-602, ISSN: 1359-6640
Self-assembling arrays of metallic nanoparticles at liquid|liquid or liquid|solid interfaces could deliver new platforms for tuneable optical systems. Such systems can switch between very-high and very-low reflectance states upon assembly and disassembly of nanoparticles at the interface, respectively. This encourages creation of electro-variably reversible mirror/window nanoplasmonic devices. However, the response time of these systems is usually limited by the rate-of-diffusion of the nanoparticles in the liquid, towards the interface and back. A large time-constant implies slow switching of the system, challenging the practical viability of such a system. Here we introduce a smart alternative to overcome this issue. We propose obtaining fast switching via electrically-induced rotation of a two-dimensional array of metal nanocuboids tethered to an ITO substrate. By applying potential to the ITO electrode the orientation of nanocuboids can be altered, which results in conversion of a highly-reflective nanoparticle layer into a transparent layer (or vice versa) within sub-second timescales. A theoretical method is developed based on the quasi-static effective-medium approach to analyse the optical response of such arrays, which is verified against full-wave simulations. Further theoretical analysis and estimates based on the potential energy of the nanoparticles in the two orientations corroborate the idea that voltage-controlled switching between the two states of a nanoparticle assembly is a viable option.
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