Junko Kagimoto

3D Interconnected Ionic Nano-Channels Formed in Polymer Films: Self-Organization and Polymerization of Thermotropic Bicontinuous Cubic Liquid Crystals

Thermotropic bicontinuous cubic (Cub(bi)) liquid-crystalline (LC) compounds based on a polymerizable ammonium moiety complexed with a lithium salt have been designed to obtain lithium ion-conductive all solid polymeric films having 3D interconnected ionic channels. The monomer shows a Cub(bi) phase from -5 to 19 °C on heating. The complexes retain the ability to form the Cub(bi) LC phase. They also form hexagonal columnar (Col(h)) LC phases at temperatures higher than those of the Cub(bi) phases. The complex of the monomer and LiBF(4) at the molar ratio of 4:1 exhibits the Cub(bi) and Col(h) phases between -6 to 19 °C and 19 to 56 °C, respectively, on heating. The Cub(bi) LC structure formed by the complex has been successfully preserved by in situ photopolymerization through UV irradiation in the presence of a photoinitiator. The resultant nanostructured film is optically transparent and free-standing. The X-ray analysis of the film confirms the preservation of the self-assembled nanostructure. The polymer film with the Cub(bi) LC nanostructure exhibits higher ionic conductivities than the polymer films obtained by photopolymerization of the complex in the Col(h) and isotropic phases. It is found that the 3D interconnected ionic channels derived from the Cub(bi) phase function as efficient ion-conductive pathways.

Nanostructured Liquid Crystals Combining Ionic and Electronic Functions

New molecular materials combining ionic and electronic functions have been prepared by using liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid crystals show thermotropic smectic A phases. Nanosegregation of the pi-conjugated mesogens and the ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of 2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic responses are observed for compound 1 without additional electrolyte solution on the application of double-potential steps between 0 and 2.5 V in the smectic A phase at 160 degrees C. In contrast, compound 2 having a tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-organized molecular redox systems can be built by nanosegregated pi-conjugated liquid crystals containing imidazolium moieties with and without electroactive thin layers on the electrodes.

Macroscopic Photocontrol of Ion-Transporting Pathways of a Nanostructured Imidazolium-Based Photoresponsive Liquid Crystal

The photocontrol of the macroscopic alignment of nanostructured 2D ion-transporting pathways is described. The uniplanar homogeneous alignment of the thermotropic smectic (Sm) liquid-crystalline (LC) phase has been successfully achieved via photoinduced reorientation of the azobenzene groups of the imidazolium-based LC material. The ionic layers of the Sm LC phase are macroscopically oriented perpendicular to the surface of the glass substrate. The oriented films show anisotropic ion conduction in the Sm phase. This is the first example of the macroscopic photoalignment of ion-conductive LC arrays. Reversible switching of homeotropic and homogeneous alignments has also been achieved for the LC material. These materials and the alignment methodology may be useful in the development of ion-based circuits and memory devices.

Anisotropic Proton-Conductive Materials Formed by the Self-Organization of Phosphonium-Type Zwitterions

or electrolyte solution substituents for energy devices such as lithium ion batteries [ 3 ] and fuel cells, [ 4 ] as a result of their unique combination of properties such as high ionic conductivity, negligibly small vapor pressure, and fl ame retardancy. For use in energy conversion devices (other than capacitors), strict requirements on the selective transport of the target ions must be met. For example, lithium ions and protons are required to be transported in the matrix for lithium (ion) batteries and fuel cells, respectively. In spite of the remarkable properties of ionic liquids, they also have drawbacks as the matrix for selective ion transport. In particular, migration of component ions lowers the transference number of target ions, such as lithium cations or protons in the ionic liquid. To overcome the problem, zwitterions, in which both cation and anion are bonded covalently, have been proposed as a medium for selective target ion transport. [ 5–8 ] The zwitterions are expected not to migrate under an applied potential gradient because of their intramolecularly neutralized charges, and the applied voltage can therefore be used to operate the target ions. In our previous studies we designed and synthesized zwitterions with relatively low melting point and/or low glass transition temperature. [ 5–7 ] Although zwitterions are generally solid at room temperature, they become liquid at room temperature upon equimolar addition of salts or acid containing bis(trifl uoromethylsulfonyl) imide anions (Tf 2 N) such as LiTf 2 N [ 6 ] or HTf 2 N. [ 7 ] It has already been shown that the Tf 2 N anions interact strongly with the cationic part of the zwitterions to provide a matrix with a low glass transition temperature. [ 6 ] The resulting liquids therefore display cation-selective transport behavior. For instance, we have

Effect of tetrabutylphosphonium cation on the physico-chemical properties of amino-acid ionic liquids

Tetraalkylphosphonium-based amino-acid ionic liquids show lower viscosities and higher decomposition temperatures (>300 degrees C) than previously reported ammonium-based amino-acid ionic liquids.

Co-organisation of ionic liquids with amphiphilic diethanolamines: construction of 3D continuous ionic nanochannels through the induction of liquid–crystalline bicontinuous cubic phases

Three-dimensionally continuous ionic nanochannels have been developed by imidazolium-based ionic liquids and amphiphilic molecules having a diethanolamine moiety. Co-organisation of these two components into liquid–crystalline bicontinuous cubic phases leads to the formation of the 3D nanochannels. The induction of bicontinuous cubic phases is observed for the combination of an ionic liquid, 1-(2-methoxyethyl)-3-methylimidazolium bromide, and a diethanolamine derivative, N-{3-[N′, N′-bis(2-hydroxyethyl) aminopropyl]}-3,4-didodecyloxy benzoylamide. Compatibility enhanced by intermolecular interactions between the imidazoliums and the diethanolamine moiety plays an important role for the co-organisation of the two components. The three-dimensionally continuous ionic nanochannels function as efficient transportation pathways for ions. The material design using bicontinuous cubic liquid–crystalline structures will offer an opportunity for the development in the field of nanochannel material science.

Novel thermotropic gels composed of only ions

Novel thermotropic physical gels were synthesized by mixing different ionic liquids without reduction of ion density due to addition of no other additives such as polymer materials or gelators.