Reaction fronts in an ionic autocatalytic system with an applied electric field

The effects of applying an electric field to an ionic autocatalytic reaction with a cubic rate law are discussed. The constant field strength approximation is made and the resulting equations for the model examined by first considering the corresponding travelling wave equations. These show ranges of field strength over which travelling waves do not exist, these ranges being dependent on whether D< 1 or D< 1, where D is the ratio of diffusion coefficients of autocatalyst and substrate. Numerical simulations of the full system are obtained and these show that, when travelling waves exist, these are formed as the long time behaviour of the system. When travelling waves do not exist, complete electrophoretic separation of the reacting ionic species results, forming separate fronts in autocatalyst and substrate, their direction of propagation depending on D. Comparisons with a related problem with a quadratic rate law are made and the implications for experiments based on the iodate–arsenous acid reaction assessed.     

Synthesis and electric field actuation of an ionic liquid polymer

Polymerizable ionic liquids and their actuation in an electric field are a combination of material and properties with unique potential to display structural and fluid dynamics above that found in small molecule ionic liquids. In an effort to blend ionic liquid nature with actuation response, we have synthesized a new ionic liquid ammonium sulfonate monomer and polymer. The liquid temperature ranges of both the monomer and polymer ionic liquid systems are quite large extending from their respective glass transitions (Tg) of -57 and -49 degrees C to decomposition at approximately 200 degrees C. Particularly remarkable is the small Tg increment that accompanies the transformation from monomer to polymer. The electrowetting behavior of the polymer and of the monomer presents an interesting contrast. This communication will encompass the polymerization, characterization, and actuation of these new ionic liquids.     

Nuclear magnetic relaxation of ionic nuclei moving in an external electric field

We have experimentally investigated nuclear magnetic relaxation of some quadrupolar ionic nuclei (²³Na⁺, ⁸⁷Rb⁺ and ³⁵Cl⁻ ) in electrolyte solutions in non-equilibrium states. The measurements of relaxation rates 1/T₁ in the presence of a direct electric field, and thus also an electric current, revealed that differences can occur in comparison with relaxation in the absence of the field. In some systems no change in the relaxation rate was observed, but in certain other (non-aqueous) systems there was a change in the quadrupolar relaxation rate in the presence of the field.     

Morphological manipulation of ionic block copolymer micelles using an electric field

We present an electric-field-triggered sphere-to-cylinder transition of negatively charged block copolymer micelles with a radically low electric field of 30 V/cm. The system investigated is dilute solutions of strong polyelectrolyte containing ionic-b-neutral block copolymers (i.e., poly(styrenesulfonate-b-methylbutylene)). We have carried out in situ small-angle X-ray scattering experiments equipped with a dc power supply, combined with electron microscopy and atomic force microscopy. The application of small electrical fields across the solutions of spherical micelles results in the transient morphology of interconnected spheres, which are eventually transformed into a cylindrical shape with time. The E-field-induced cylindrical micelles revert to spherical micelles when the E field is switched off.     

Novel transmittance change of polyelectrolyte hydrogel in DC electric field

A novel transmittance change of poly(acrylamide‐co‐acrylic acid) hydrogel in a DC electric field was observed. Transmittance of a specimen increased when the electric field was on and decreased by removing the electric force. In certain cases, the sample was able to switch from white opaque to colorless transparent. The rate and extent of the transition depended on the applied electric potential, ambient temperature, and composition of the specimen. These observations are closely related to the dissociation of hydrogen bonding in the network induced by an external electric field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2290–2295, 2003     

Dynamic light scattering of an ionic SDS micellar solution under an AC electric field

The phase separation behavior of near-critical ionic sodium-dodecyl-sulfate (SDS) micellar solution under a sinusoidal electric field was investigated by phase-contrast optical microscopy and by the small-angle dynamic light scattering method. The sinusoidal electric field significantly deformed the concentration domains and shifted the phase separation temperature. The autocorrelation function under a sinusoidal electric field was measured in the vicinity of a phase separation temperature range of 0.10 K < T_p – T < 0.97 K, where T_p – T is the temperature distance from the phase separation temperature in quiescent state T_p. The correlation function with an oscillatory part in the longer correlation time region was observed. The occurrence of the oscillatory mode, which depended on both the applied field frequency and the ambient temperature, indicates deformation of concentration fluctuation domains by dynamical coupling between the phase separation and the applied sinusoidal electric field. Received: 9 June 2000 Accepted: 31 August 2000     

Resonant increase of ionic conductance of yttria-stabilized zirconia in an alternating external electric field

Journal of Solid State Electrochemistry - The effect of an external alternating electric field on the diffusion of O2− ions in yttria-stabilized zirconia was studied by the molecular dynamics...     

Effects of an electric field on interaction of aromatic systems

The effect of uniform external electric field on the interactions between small aromatic compounds and an argon atom is investigated using post‐HF (MP2, SCS‐MP2, and CCSD(T)) and density functional (PBE0‐D3, PBE0‐TS, and vdW‐DF2) methods. The electric field effect is quantified by the difference of interaction energy calculated in the presence and absence of the electric field. All the post‐HF methods describe electric field effects accurately although the interaction energy itself is overestimated by MP2. The electric field effect is explained by classical electrostatic models, where the permanent dipole moment from mutual polarization mainly determines its sign. The size of π‐conjugated system does not have significant effect on the electric field dependence. We found out that PBE0‐based methods give reasonable interaction energies and electric field response in every case, while vdW‐DF2 sometimes shows spurious artifact owing to its sensitivity toward the real space electron density. © 2015 Wiley Periodicals, Inc.     

Phase behavior of a simple dipolar fluid under shear flow in an electric field

Nonequilibrium molecular dynamics simulations are performed on a dense simple dipolar fluid under a planar Couette shear flow. Shear generates heat, which is removed by thermostatting terms added to the equations of motion of the fluid particles. The spatial structure of simple fluids at high shear rates is known to depend strongly on the thermostatting mechanism chosen. Kinetic thermostats are either biased or unbiased: biased thermostats neglect the existence of secondary flows that appear at high shear rates superimposed upon the linear velocity profile of the fluid. Simulations that employ a biased thermostat produce a string phase where particles align in strings with hexagonal symmetry along the direction of the flow. This phase is known to be a simulation artifact of biased thermostatting, and has not been observed by experiments on colloidal suspensions under shear flow. In this paper, we investigate the possibility of using a suitably directed electric field, which is coupled to the dipole moments of the fluid particles, to stabilize the string phase. We explore several thermostatting mechanisms where either the kinetic or configurational fluid degrees of freedom are thermostated. Some of these mechanisms do not yield a string phase, but rather a shear-thickening phase; in this case, we find the influence of the dipolar interactions and external field on the packing structure, and in turn their influence on the shear viscosity at the onset of this shear-thickening regime.     

Nonlinear response of aluminum surface to electric field

The static limit of the perpendicular second-harmonic response of the exposed single-crystal planes of aluminum to applied electric field is studied using the variant of stabilized-jellium model which allows to account for the anisotropy of surface potential. The self-consistently calculated linear and second-order induced charge density distributions are used to determine the normal component of the polarization vector. The surface structure is found to have a pronounced effect on the anisotropy of second-harmonic response. © 1997 John Wiley & Sons, Inc.     

The influence of an electric field on the wetting of an SiO2 film by ionic liquids

The electrowetting of a dielectric SiO₂ film 100 nm thick by drops (D = 2–3 mm) of [C₄mIm][PF₆], [C₆mIm][PF₆], and [C₆mIm][BTI] ionic liquids was studied at |U| ≤ 60 V in a ～10^?8 mbar vacuum. Electrocapillary curves of the dependence of the wetting angle on electric field potential were constructed with an accuracy of ±1 deg. In conformity with the Young-Lippman equation, the wetting angle θ° decreased by the parabolic law from 51° to 43° for [C₄mIm][PF₆], from 48° to 38° for [C₆mIm][PF₆], and from 35° to 27° for [C₆mIm][BTI] as |U| increased at 298 K. The electrocapillary curve branches were situated symmetrically in the (θ°, U) coordinates with respect to the line passing through the point U = 0; that is, zero-charge potential is zero for the electrowetting of the dielectric film by the ionic liquids. The capacitance of the double electrical layer at the ionic liquid-dielectric interface was determined. This value was found to be 4.65, 2.93, and 1.73 μF/m² for the electrowetting of the SiO₂ film at 298 K by the ionic liquids specified, respectively.     

Lyotropic liquid crystalline phase behaviour in amphiphile-protic ionic liquid systems

Approximate partial phase diagrams for nine amphiphile-protic ionic liquid (PIL) systems have been determined by synchrotron source small angle X-ray scattering, differential scanning calorimetry and cross polarised optical microscopy. The binary phase diagrams of some common cationic (hexadecyltrimethyl ammonium chloride, CTAC, and hexadecylpyridinium bromide, HDPB) and nonionic (polyoxyethylene (10) oleyl ether, Brij 97, and Pluronic block copolymer, P123) amphiphiles with the PILs, ethylammonium nitrate (EAN), ethanolammonium nitrate (EOAN) and diethanolammonium formate (DEOAF), have been studied. The phase diagrams were constructed for concentrations from 10 wt% to 80 wt% amphiphile, in the temperature range 25 °C to >100 °C. Lyotropic liquid crystalline phases (hexagonal, cubic and lamellar) were formed at high surfactant concentrations (typically >50 wt%), whereas at <40 wt%, only micelles or polydisperse crystals were present. With the exception of Brij 97, the thermal stability of the phases formed by these surfactants persisted to temperatures above 100 °C. The phase behaviour of amphiphile-PIL systems was interpreted by considering the PIL cohesive energy, liquid nanoscale order, polarity and ionicity. For comparison the phase behaviour of the four amphiphiles was also studied in water.     

Crystal nucleation in an electric field

Nucleation of polar and apolar crystals in an electrostatic field has been analyzed. The analysis is based on the extended nucleation theory which takes into account orientation of amorphous kinetic elements and the resulting crystals. In an electric field free energy of transformation is orientation-dependent which leads to orientation and field effects in thermodynamic (critical crystallization temperature) and kinetic crystallization characteristics (thermal and athermal nucleation rates).     

Self-discharge characteristics of an electric double-layer capacitor with polymer hydrogel electrolyte

An electric double-layer capacitor (EDLC) was assembled with the polymer hydrogel electrolyte prepared from cross-linked potassium poly(acrylate) (PAAK) and KOH aqueous solution, and the self-discharge characteristics were investigated. The EDLC cell with the polymer hydrogel electrolyte showed lower voltage decay on open circuit than that with a KOH aqueous solution. Moreover, it was found that the leakage current of the EDLC cell was markedly suppressed by using the polymer hydrogel electrolyte. The suppression was enhanced with increasing PAAK content in the electrolyte. These results strongly suggest that the PAAK plays an important role in the suppression of self-discharge.     

Non-joule heating of ice in an electric field

We theoretically predict and calculate non-Joule heating/cooling caused by a direct electric current in ordinary crystalline ice Ih. The cause of this effect is related to partial ordering/disordering occurring in the proton subsystem of ice when protons either drift or diffuse in the ice. Depending on relative directions of the electric current and the configuration vector of ice, the non-Joule effect can be either positive, that is, heat generation, or negative, that is, heat absorption, and its absolute magnitude is usually comparable with that of normal Joule heating. The magnitude of this phenomenon is also approximately inversely proportional to the ice temperature and, thus, is more pronounced at low temperatures.     

Orientation of native cellulose in an electric field

Native cellulose has been oriented in an ac electric field at both the macroscopic and colloidal level. Ramie fiber fragments suspended in chloroform have been shown to point along the field. Cellulose microcrystal suspensions in cyclohexane have also been allowed to evaporate in an electric field and have exhibited a high degree of orientation when further examined by TEM and electron diffraction. Similarly, cellulose whisker suspensions showed increasing birefringence with increasing field strength and displayed interference Newton colors that saturated at around 2000 V cm(-)(1). A high degree of order of this suspension was also obtained by evaluating the induced birefringence with color charts.