Anisotropic Ionic Conductivity Research Articles

Phase transition and anisotropic conductivity in guanidine zinc sulfate crystals

The guanidine zinc sulfate [C(NH 2) 3] 2Zn(SO 4) 2 – abbreviated as GZS – crystal was grown and characterized by the calorimetric and dielectric investigations. Basing on the specific heat measurements the second order structural phase transition at temperature of about 178 K was found. The anisotropic ionic conductivity of GZS was observed in the complex dielectric measurements performed in wide temperature and frequency ranges: 140–320 K and 10 0–10 6 Hz, respectively. The activation energy of the conduction process measured along [110] direction varies from 0.43 eV in low temperature to 0.28 eV in high temperature phase. The activation energy in the [001] direction in the high temperature phase equals to 0.43 eV. The low frequency dielectric relaxation process of activation type in GZS crystals was found.

Anisotropic Ionic Conductivity in Block Copolymer Membranes by Magnetic Field Alignment

The self-assembly of diblock copolymers provides a convenient route to the formation of mechanically robust films with precise and tunable periodic arrangements of two physically demixed but chemically linked polymeric materials. Chemoselective transport membranes may be realized from such films by selective partitioning of an active species into one of the polymer domains. Here, lithium ions were selectively sequestered within the poly(ethylene oxide) block of a liquid crystalline diblock copolymer to form polymer electrolyte membranes. Optimization of the membrane conductivity mandates alignment of self-assembled structures such that conduction occurs via direct as opposed to tortuous transport between exterior surfaces. We show here that magnetic fields can be used in a very simple and scalable manner to produce highly aligned hexagonally packed cylindrical microdomains in such membranes over macroscopic areas. We systematically explore the dependence of the ionic conductivity of the membrane on both temperature and magnetic field strength. A surprising order of magnitude increase in conductivity relative to the nonaligned case is found in films aligned at the highest magnetic field strengths, 6 T. The conductivity of field aligned samples shows a nonmonotonic dependence on temperature, with a marked decrease on heating in the proximity of the order-disorder transition of the system before increasing again at elevated temperatures. The data suggest that domain-confined transport in hexagonally packed cylindrical systems differs markedly in anisotropy by comparison with lamellar systems.

Effects of Alkyl Chain Length on Properties of 1‐Alkyl‐3‐methylimidazolium Fluorohydrogenate Ionic Liquid Crystals

A series of 1-alkyl-3-methylimidazolium fluorohydrogenate salts (C(x)MIm(FH)(2)F, x=8, 10, 12, 14, 16, and 18) have been characterized by thermal analysis, polarized optical microscopy, IR spectroscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. Liquid crystalline mesophases with a smectic A interdigitated bilayer structure are observed from C(10) to C(18), showing a fan-like or focal conic texture. The temperature range of the mesophase increases with the increase in the alkyl chain length (from 10.1 °C for C(10)MIm(FH)(2)F to 123.1 °C for C(18)MIm(FH)(2)F). The distance between the two layers in the smectic structure gradually increases with increasing alkyl chain length and decreases with increasing temperature. Conductivity parallel to the smectic layers is around 10 mS cm(-1) regardless of the alkyl chain length, whereas that perpendicular to the smectic layers decreases with increasing alkyl chain length because of the thicker insulating sheet with the longer alkyl chain.

Anisotropic ionic conductivities in lyotropic supramolecular liquid crystals

The designed aromatic amide discotic molecule with sulfonic acid groups at its periphery exhibits a hexagonal supramolecular columnar liquid crystalline phase, which leads to the achievement of anisotropic ionic conductivity through macroscopically aligning the ionic channels.

Uniaxially Parallel Alignment of a Smectic A Liquid-Crystalline Rod−Coil Molecule and Its Lithium Salt Complexes Using Rubbed Polyimides

The alignment behavior of thermotropic smectic A liquid-crystalline molecule 1 and its complexes with lithium triflate on the thin films of rubbed polyimides has been examined. Compound 1 has a rod−coil block structure consisting of a tetra(ethylene oxide) chain that is polar and a phenylcyclohexyl mesogen that is nonpolar. The use of a rubbed polyimide having a linear and rigid molecular structure prepared from pyromellitic dianhydride and 1,4-phenylenediamine induces the uniaxially parallel alignment of 1 and its lithium triflate complexes. The lithium salt complexes of compound 1 that exhibit smectic A phases function as two-dimensional ion conductors. The ionic conductivities of the aligned complexes of 1 on the rubbed polyimides were measured by an ac impedance method. Anisotropic ionic conductivities have been observed for the aligned liquid-crystalline lithium salt complexes.

Liquid-Crystalline Formation and Functionalization of Ionic Liquids through Self-Organization Processes

Self-assembly of liquid-crystalline molecules that combine order and fluidity is one of promising approaches to the preparation of nanostructured functional materials. Here we present a development of liquid-crystalline materials exhibiting anisotropic ionic conductivities by self-organization of ionic liquids. A new class of liquid-crystalline materials with layered (smectic) and cylindrical (columnar) structures was prepared by supramolecular association of conventional ionic liquids and hydrogen-bonded mesogenic molecules and by the chemical modification of ionic liquids. These materials formed nano-segregated structures consisting of ion-conducting and insulating parts in the liquid-crystalline states. Anisotropic ionic conductivities were induced by the formation of a single domain in the liquid-crystalline phases and the macroscopic alignment of the ion-conductive paths. Free-standing ion-conductive polymer films were also prepared by fixation of aligned structures of polymerizable liquid-crystalline ionic liquids through photoirradiation.

Organosiloxane liquid crystals for fast-switching bistable scattering devices

In this paper, we investigate the dependence of the bistable electro-optic response of organosiloxane based smectic A liquid crystals on key material properties; the modes are optically scattering (<100 Hz) and clear (>1 kHz), respectively. The scattering mode is generated by motion of doped ionic species and is dependent upon the conductivity anisotropy of the liquid crystal; the clear mode occurs through dielectric coupling at frequencies sufficient to inhibit ionic conduction. The pure siloxane liquid crystals exhibit unusually high anisotropic ionic conductivities; the ratio of the components parallel and perpendicular to the director is up to 0.005; for analogous non-siloxane based liquid crystals the value is ∼0.5. However, the pure materials possess low dielectric anisotropy compared with similar polar liquid crystals, e.g. 0.8 compared with 8.4. Based upon these observations, we prepare exemplar mixtures of organosiloxane with 4-(ω-pentyloxy)-4′-cyanobiphenyl (5OCB) as a dielectric additive. These systems show beneficial properties: highly anisotropic conductivity coupled with an increase in the dielectric anisotropy. As a result, the electro-optic responses of these mixtures show a significant improvement upon the pure compounds; for example, for the 49% w/w mixture it is found that the response time of the optically clear mode is significantly reduced, e.g. from 130 ms (at 280 V rms) to 5 ms at an applied voltage of 102 V rms. We conclude that simple mixtures, using an organosiloxane as the bulk component, have much promise for use in bistable, electro-optic storage and display devices.

One-Dimensional Ion-Conductive Polymer Films: Alignment and Fixation of Ionic Channels Formed by Self-Organization of Polymerizable Columnar Liquid Crystals

We have prepared two types of one-dimensional ion-conductive polymer films containing ion nanochannels that are both perpendicular and parallel to the film surface. These films have been obtained by photopolymerization of aligned columnar liquid crystals of a fan-shaped imidazolium salt having acrylate groups at the periphery. In the columnar structure, the ionic part self-assembles into the inner part of the column. The column is oriented macroscopically in two directions by different methods: orientation perpendicular to the modified surfaces of glass and indium tin oxide with 3-(aminopropyl)triethoxysilane and orientation parallel to a glass surface by mechanical shearing. Ionic conductivities have been measured for the films with columnar orientation vertical and parallel to the surface. Anisotropic ionic conductivities are observed for the oriented films fixed by photopolymerization. The ionic conductivities parallel to the columnar axis are higher than those perpendicular to the columnar axis because the lipophilic part functions as an ion-insulating part. The film with the columns oriented vertically to the surface shows an anisotropy of ionic conductivities higher than that of the film with the columns aligned parallel to the surface.

Nano-Segregated Polymeric Film Exhibiting High Ionic Conductivities

Nanostructures can be used for the fabrication of highly functional materials transporting ions and charges. We demonstrate a new design strategy for polymeric higher ion-conductors. Phase-segregated layers of alternating mobile tetra(ethylene oxide)s (TEOs) and rigid aromatic cores where the TEO moieties are grafted from aromatic layers have been shown to be efficient to transport lithium triflate. Such segregated structures at the nanometer scale (nano-segregated structures) were prepared by in-situ photopolymerization of an aligned methacrylate liquid crystalline monomer comprising a terphenyl rigid rod mesogen having a TEO terminal chain. The ion-conductive TEO moiety remains in the highly mobile state even after polymerization, which is indicated by its low glass transition temperature (-45 degrees C). This nanostructured film exhibits an ionic conductivity parallel to the layer of 10(-3) S cm(-1) at room temperature. The highest ionic conductivity is in the level of 10(-2) S cm(-1) observed at 150 degrees C. The anisotropic ionic conductivities have been observed for the nano-segregated film.

SELF-ASSEMBLY OF AN IONIC LIQUID AND A HYDROXYL-TERMINATED LIQUID CRYSTAL: ANISOTROPIC ION CONDUCTION IN LAYERED NANOSTRUCTURES

Anisotropic ion-conductive materials have been prepared by self-assembly of a conventional ionic liquid and a hydroxyl-terminated liquid crystal. These assemblies form phase-segregated layered structures on the nanometer scale. Anisotropic ionic conductivities along the direction parallel and perpendicular to the layer have been successfully measured for the sample forming oriented monodomains. The ionic conductivity parallel to the layer (σi//) is higher than that perpendicular to the layer (σi⊥). The maximal anisotropy (σi///σi⊥) is 2.6 × 103 at 37°C in the smectic B phase.

Ion-conductive mechanism in liquid crystalline molecules having polyether segment

A series of liquid crystalline molecules, α,ω-bis{4-[(4′-pentyloxy (or -octyloxy)-4-biphenylyl)-carbonyloxy]phenyl}oligo(oxyethylene)s, was synthesized to prepare oriented oligo(oxyethylene) chains. The complexes with LiCF 3SO 3 spontaneously formed a smectic phase. Since a rigid rod part cannot solubilize the inorganic salts, the oxyethylene moieties form the ion-conductive layers in the smectic phase. The anisotropic ionic conductivity was measured by an impedance analyzer with gold comb-shaped electrode deposited on a glass substrate between Au teeth. The ionic conductivity between the gold teeth increased to 10 −3 S cm −1 at 142 °C, but it dropped considerably to 10 −4 S cm −1 above that temperature. The temperature corresponded to the isotropization point of the complex. Homeotropic orientation of the liquid crystalline complex enables to make a successive ion-conducting pathway, which is effective to obtain higher ionic conductivity. The effect of the added salts on the ionic conductivity was also analyzed. Higher ionic conductivity was obtained when the liquid crystals were complexed with LiCF 3SO 3. There is a suitable ion size for prompt ion migration in the oriented polyether.

Anisotropic ionic conductivity of lithium-doped sulfonated PBI

The conductivity study results of lithium-doped sulfonated PBI, a conjugated rigid rod polymer, poly[(1,7-dihydrobenzo[1,2-d:4,5-d′]dimidazole-2,6-diyl)-2-(2-sulfo)-p-phenylene], derivatized with pendants of propane sulfonate Li+ ionomer are reported. The room-temperature DC four-probe conductivity parallel to the surface of cast films was as large as 8.3 × 10−3 S/cm. Similar measurements with an eight-probe configuration showed no difference between bulk and surface conductivity. The ionic nature of the conductivity was indicated by constant voltage depletion experiments and by secondary ion mass spectroscopy measurements of the residues near the electrodes. The DC two-probe conductivity measured transverse to the sample surface was three to four orders of magnitude smaller than longitudinal conductivity, while the AC two-probe conductivity was even less. Electron microscopy indicated that the films had a layered structure parallel to the surfaces. This structural anisotropy was confirmed by refractive index values obtained from wave-guide experiments and by wide angle X-ray scattering. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2925–2933, 1997

Anisotropic Ionic Conductivity Observed in Superplastically Deformed Yttria‐Stabilized Zirconia/Alumina Composite

Ionic conductivity measurements on a yttria‐stabilized tetragonal zirconia polycry stall alumina composite subjected to superplastic deformation demonstrate anisotropic character. Parallel to the pressing direction, the grain‐boundary resistance to oxygen ion mobility is 25% to 30% higher than that measured perpendicular to the pressing direction. The same directional dependency on the volume conductivity is observed but is less pronounced, showing approximately a 9% difference. Microstructural evidence reveals an agglomeration and elongation of alumina particles perpendicular to the pressing direction, and it is suggested that this phenomenon restricts the passage of ions parallel to the compression direction, giving rise to the anisotropic nature of the conductivity measurements.

Haven ratio and correlation effects in diffusion in li3N

Abstract We define a modified Haven ratio Hnmr using NMR-experiments instead of tracer diffusion techniques. The derived experimental values of Hnmr show that the anisotropic ionic conductivity in Li3N can be completely described in terms of two diffusion processes determined from NMR observables: an intra-layer process within the Li2N layers only and an inter-layer process involving both Li sites. The comparision of Hnmr obtained by a computer simulation with the corresponding experimental value confirm the idea of a vacancy-induced migration of Li ions in the Li2N layers.