Hirosato Monobe

Shaping liquid on a micrometre scale using microwrinkles as deformable open channel capillaries

Methods of shaping and manipulating liquids on small scales are important for micro-patterning, microfluidics and biosensing, and may provide fundamental insights into phenomena in confined small spaces. Here, we report a simple technique for shaping liquids into micrometre-scale filaments. Microgrooves on microwrinkles generated by thin film buckling on elastic substrates can function as open channel capillaries for liquids with appropriate wettabilities. Tuning the groove depth of the microwrinkles by modulating strain, we explore the capillary action of various liquids in microgrooves, which form liquid filaments emanating from a large reservoir. This behaviour is explained in terms of sinusoidal-geometry-dependent surface energy. Based on this concept, a regular array of liquid filaments can be formed over a large area by a simple coating method, and these filaments can be further reshaped by exploiting strain-induced nonlinear changes in microwrinkle topography. This technology shows promise for applications in micro-patterning, nano- and micro-reactors, and microfluidics.

High Carrier Mobility up to 1.4 cm2·V-1·s-1in Non-Peripheral Octahexyl Phthalocyanine

Carrier transport properties of a non-peripherally alkyl-substituted phthalocyanine, 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) have been investigated. The material is a low-molecular-weight organic semiconductor with high solubility for typical organic solvents and liquid crystallinity. The carrier mobility was measured in the crystal phase and the hexagonal disordered columnar (Colhd) mesophase by the time-of-flight technique. A strong negative temperature dependence was observed for the hole mobility in the crystal phase, and a maximum drift mobility of 1.4 cm2·V-1·s-1 was achieved at -15 °C. A maximum mobility of 0.5 cm2·V-1·s-1 was obtained for the electrons that had a smaller dependence.

Highly localized photochemical processes in LB films of photo chromic material by using a photon scanning tunneling microscope

Abstract A highly localized evanescent light from a fiber probe with a 100 nm diameter aperture of a photon scanning tunneling microscope (PSTM) was used to realize localized photochemical processes in LB films of photochromic material. The localized photochemical processed region sized as small as 130 nm was obtained by using the transmission type PSTM.

Photoconductivity of liquid crystalline derivatives of pyrene and carbazole

Two structurally related discogens containing either pyrene (1a) or carbazole (2a) were investigated by thermal, XRD, spectroscopic, and time-of-flight (TOF) methods. Experiments demonstrated for 1a a narrow range Colh phase, which easily forms a glass state at ambient temperature. TOF measurements showed an ambipolar charge transport for 1a with the mobilities on the order of 10−3 cm2 V−1 s−1. The carbazole 2a has two enantiotropic phases (Crcol and Colh) and behaves as a p-type semiconductor. The activation energy for positive charge mobility in 1a was found to be 0.10 ± 0.01 eV.

Microwrinkles: Shape-tunability and applications

Recently, spontaneously formed microwrinkle patterns on hard coating-capped elastomer surfaces have attracted the attention of both the scientific and applied research communities, because of their simple fabrication process and practical potential in diverse applications. The periodicity and statistical orientation of the microwrinkle stripes can be controlled by applying uniaxial or isotropic compressive strain. Thus, microwrinkles have been applied to cell patterning, optical gratings, pattern templates for further patterning, surfaces with anisotropic wetting properties, surfaces with unique adhesion properties, and metrology of ultrathin film properties. Our group has focused on tuning the structure of microwrinkles by exerting additional strain. This is almost impossible for micropatterns fabricated on a hard Si wafer; therefore, our technique is based on a soft substrate and the non-linear response of the system to external strain. The dynamic shape-tunability of the micropatterns shows potential for new applications, in which switching states of a system could be induced by a change in the physical boundary conditions, namely, the shape of microwrinkles. This feature article summarizes our laboratorys recent work on controlling the stripe pattern of microwrinkles and the application of shape-tunable microwrinkles to liquid manipulation and liquid crystal alignment. For liquid manipulation, the microgrooves of the microwrinkles are used as an open channel capillary, in which the tunable groove depth controls the capillary action of the liquid in the grooves. Further changes in the direction of the microgrooves, which are filled with liquid, can induce the division of the liquids into small droplets. Such methods for shaping liquids are made possible by only macroscopic control of the strain applied to the sample. The alignment of a nematic liquid crystal was also investigated. Nematic liquid crystals can be aligned by anisotropic microgrooves; therefore, we have demonstrated that microwrinkles can be used for this purpose. In addition, because microwrinkles are shape-tunable, the liquid crystal alignment could be repeatedly switched. Our research demonstrates that shape-tunable microwrinkles provide new physical boundary conditions that can control the states of the bounded material, for example: the shape of liquid droplets and the alignment of a nematic director. We expect that many other systems that interact with the tunable boundary will lead to the discovery of new phenomena and technologies.

Photoconductive Liquid-Crystalline Derivatives of 6-Oxoverdazyl

1,3,5-Triphenyl-6-oxoverdazyl radicals 1[n], in which each phenyl group is substituted with three alkylsulfanyl groups (n = 6, 8, 10), exhibit a monotropic columnar rectangular (Col(r)) phase below 60 °C. Detailed analysis of 1[n] revealed a broad absorption band in the visible region with maxima at 540 and 610 nm and redox potentials E(1/2)(0/+1) = +0.99 V and E(1/2)(0/-1) = -0.45 V vs SCE. Photovoltaic studies of 1[8] demonstrated a hole mobility of 1.52 × 10⁻³ cm² V⁻¹ s⁻¹ in the mesophase with an activation energy of 0.06 ± 0.01 eV. Magnetization studies of 1[8] revealed nearly ideal paramagnetic behavior in either the solid or fluid phase above 200 K and weak antiferromagnetic interactions at low temperatures.

Mesomorphic properties of copolyesters of 3,6-linked triphenylene-based units and polymethylene spacers

Main chain discotic liquid crystalline polymers consisting of triphenylene-based units and alkyl spacers (C8, C10 and C12), connected by ester linkages in the 3- and 6-positions of triphenylene, have been synthesized and their mesomorphic properties were studied by DSC, polarizing optical microscopy and X-ray diffraction. It was found that these polymers exhibit a hexagonal columnar (Colh) mesophase with intracolumnar order over a wide temperature range. The clearing temperature decreases on increasing the spacer length. It was found that the clearing temperatures are rather higher than that of the corresponding triphenylene monomer having six hexyloxy chains. These polymers form an ordered columnar mesophase, while the corresponding monomeric mesogen shows a disordered columnar phase. In the polymeric system, the fluctuations of the disc-like units in the mesophase are restricted by the connection of the mesogenic units, which stabilizes the columnar mesophase.

Liquid crystals containing a 2,6-disubstituted anthracene core—mesomorphism, charge transport and photochemical properties

The synthesis of 2-(4-phenyl)-6-anthracenes and 4,4′-bisphenyl-2,6-anthracenes, disubstituted by saturated (decyloxy) or unsaturated ((Z)-dec-4-enyloxy) chains, is reported. All the materials are liquid crystals and exhibit smectic A and/or C phases. As compared to the saturated chains, the unsaturated ones provide a significant decrease of the transition temperatures. The presence of the central “lath-like” anthracene core in the rigid aromatic moiety is found to induce some molecular π-stackings, at short range, in the mesophases. This molecular peculiarity is thought to be in a large part responsible for the high charge-carrier mobility values measured (i.e. 2 × 10−3 cm2 V−1 s−2), despite the disordered character of the mesophases. Preliminary examination of photodimerisation revealed that the formation of photoadducts was very poor in the smectic phases as compared to the same experiment run in solution. This result was attributed to the instability of the anthracene photodimers at the too high temperatures of the mesophases.

Liquid crystalline and charge transport properties of double-decker cerium phthalocyanine complexes

A homologous series of new thioalkylated double-decker cerium phthalocyanine complexes, [(CnH2n+1S)8Pc]2Ce, were synthesised and their mesomorphisms were clarified by DSC, polarized optical microscopy and X-ray diffraction. Unlike other lanthanide phthalocyanines, these double-decker cerium compounds were found by spectroscopy and X-ray crystallography to be neutral complexes. A hexagonal columnar mesophase (Colh) was exhibited by all homologues prior to melting to the isotropic liquid. Interestingly, the columnar mesophases of these compounds showed strong tendencies for spontaneous homeotropic alignment on non-treated glass substrates or ITO coated glass. The hole mobility in the Colh mesophase of the longer chain homologue was successfully measured by a TOF technique as having a value of 7 × 10−3 cm2 V−1 s−1.

Anion-driven mesogenicity: ionic liquid crystals based on the [closo-1-CB9H10]−cluster

Two series of structurally analogous esters (1) and diazenes (2) derived from the [closo-1-CB9H10]− anion and containing two or three rings in the rigid core were prepared and their liquid crystalline properties investigated. Salts containing NMe4+ or NHEt3+ counterion do not exhibit mesophases, whereas the ion pairs with N-butyl-4-heptyloxypyridinium cation [Pyr] exhibit SmA and occasionally soft crystalline phases in the temperature range of 90–180 °C. Three representative ionic liquid crystals, 1d[Pyr], 1f[Pyr] and 2d[Pyr], were investigated by powder XRD. Absorption spectroscopy demonstrated that ester 1e[Pyr] is transparent above 280 nm and the diazene 2e[Pyr] exhibits absorption bands typical for azobenzene derivatives.