Tomohiro Mukai

Noncovalent Approach to One-Dimensional Ion Conductors: Enhancement of Ionic Conductivities in Nanostructured Columnar Liquid Crystals

Noncovalent design of new liquid-crystalline (LC) columnar assemblies based on an ionic liquid has shown to be useful to achieve anisotropic high ionic conductivities. An equimolar mixture of an ionic liquid, 1-butyl-3-methylimidazolium bromide, and 3-[3,4,5-tri(octyloxy)benzoyloxy]propane-1,2-diol, which is partially miscible with the ionic liquid, exhibits an LC hexagonal columnar phase from -4 to 63 degrees C. This columnar supramolecular assembly forming the nanostructures shows the one-dimensional (1D) ionic conductivity of 3.9 x 10(-3) S cm(-1) at 50 degrees C along the column, which is more than 700 times higher than that of the corresponding covalent-type columnar ionic liquid, 1-methyl-3-[3,4,5-tri(octyloxy)benzyl]imidazolium bromide, which is 5.3 x 10(-6) S cm(-1) at 50 degrees C. This significant enhancement of the ionic conductivity is attributed to the increase of the mobility of the ionic part.

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 liquid crystals: Formation of stable smectic semi-bilayers by the introduction of perfluoroalkyl moieties†

Liquid-crystalline compounds 1 and 3 having perfluoroalkyl-terminated mesogens at both ends of poly(ethylene oxide) chains have been prepared. These compounds show smectic A (S A ) and C phases over 100 °C. The S A -Iso (isotropic) transition temperatures are higher by about 70 °C than those of the corresponding alkyl-substituted compounds 2 and 4. The incorporation of lithium triflate into 1 and 3 widens the temperature ranges of the S A phases for the resulting complexes. The complexes of 1 and 3 containing 50 mol-% of lithium triflate exhibit columnar phases. The ionic conductivities of the homotropically aligned complexes based on 1 along the direction perpendicular to the molecular director of the S A phases are higher than those of the corresponding compound of 2. The increase of the ionic conductivities as well as the stabilization of the smectic phases for these perfluoroalkyl-terminated compounds may be due to the formation of more stabilized layered structures through the intermolecular interactions among the perfluoroalkyl moieties.

Spiropyran-based liquid crystals: the formation of columnar phases via acid-induced spiro–merocyanine isomerisation

Hexagonal columnar liquid-crystalline phases are induced for a new fan-shaped spiropyran compound as the result of an acidichromism effect of spiro-merocyanine isomerisation through protonation upon incorporation of 4-methylbenzenesulfonic acid.

Self-Organized Ion-Conductive Liquid Crystals: Lithium Salt Complexes of Mesogenic Dimer Molecules Exhibiting Smectic A Phases

Abstract Liquid-crystalline dimeric molecules consisting of rigid mesogenic cores and flexible oxyethylene spacers have been prepared. The ethoxy carbonyl and alkoxy groups are attached to the ends of the mesogenic cores. These molecules have been complexed with lithium triflate, resulting in thermal stabilization of the mesophases. Ionic conductivities along the direction perpendicular to the molecular director of the smectic A phases have been measured for these complexes.

Ion-conductive mechanism in liquid crystalline molecules having polyether segment

Abstract 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 3 SO 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 3 SO 3 . There is a suitable ion size for prompt ion migration in the oriented polyether.

Two Dimensionally Ion-Conductive Liquid Crystals of Cholesterol/Tetra(Ethylene Oxide) Block Molecules

ABSTRACT Two-dimensionally ion-conductive liquid crystals have been simply obtained by self-assembly of a cholesterol/tetra(ethylene oxide) block molecule and lithium triflate. Nanophase-segregation between cholesterol and tetra(ethylene oxide) blocks leads to the formation of a smectic A liquid crystalline phase in a wide range of temperature. A homeotropically aligned lithium salt complex in the smectic A phase shows two-dimensional ionic conductivity. The ionic conductivities parallel to the smectic layers are higher than those perpendicular to the layers. The maximum value of the anisotropy in the ionic conductivity is about 2.4 × 103 at 30°C.