Ryohei Ishige

Large-scale self-assembled zirconium phosphate smectic layers via a simple spray-coating process

The large-scale assembly of asymmetric colloidal particles is used in creating high-performance fibres. A similar concept is extended to the manufacturing of thin films of self-assembled two-dimensional crystal-type materials with enhanced and tunable properties. Here we present a spray-coating method to manufacture thin, flexible and transparent epoxy films containing zirconium phosphate nanoplatelets self-assembled into a lamellar arrangement aligned parallel to the substrate. The self-assembled mesophase of zirconium phosphate nanoplatelets is stabilized by epoxy pre-polymer and exhibits rheology favourable towards large-scale manufacturing. The thermally cured film forms a mechanically robust coating and shows excellent gas barrier properties at both low- and high humidity levels as a result of the highly aligned and overlapping arrangement of nanoplatelets. This work shows that the large-scale ordering of high aspect ratio nanoplatelets is easier to achieve than previously thought and may have implications in the technological applications for similar materials.

Synthesis of diphenyl-diacetylene-based nematic liquid crystals and their high birefringence properties

We synthesized two series of diphenyl-diacetylene (DPDA)-based materials with alkoxy and alkyl tails of length m (DPDA–OCm and DPDA–Cm, respectively), and measured their nematic-phase birefringence (Δn) as a function of wavelength and temperature. We found that Δn decreases with an increase in m, possibly by a dilution effect of the low-Δn alkyl tail. Further, of the two series, Δn was found to be relatively higher in the DPDA–OCm materials, with the highest value of 0.4 obtained for DPDA–OC1 at 550 nm at 10 °C below the isotropic-to-nematic transition temperature. Further, we observed the temperature dependence for Δn, which is proportional to the order parameter (s). From extrapolation to s = 1 (the perfect orientation state), it is speculated that the DPDA–O moiety has the potential to afford a very large Δn of 0.9.

Control over Internal Structure of Liquid Crystal Polymer Nanofibers by Electrospinning

Liquid crystal polymer nanofibers with a diameter ranging from 0.13 to 4.71 µm were prepared by electrospinning from a main-chain liquid crystalline polyester, BB-5(3-Me). WAXD measurements showed that the formation and orientation of the ordered structure in the electrospun fibers were controlled by the fiber diameter formed during electrospinning. For BB-5(3-Me), the SmA structure with two layer spacings was formed in the fiber during the electrospinning. Under optimal spinning conditions, the SmA structure is highly oriented in the fiber. In addition, annealing transformed the metastable SmA structure in the BB-5(3-Me) fiber into stable SmCA one.

Molecular design of environmentally benign segmented polyurethane(urea)s: effect of the hard segment component on the molecular aggregation states and biodegradation behavior

We investigated the molecular aggregation states, mechanical properties, and biodegradability of environmentally benign segmented polyurethane(urea)s [SPU(U)s], which contained bio-based monomers of an α-amino acid lysine-based diisocyanate (LDI). The SPU(U)s consisted of an aliphatic diisocyanate (LDI or 1,4-butanediisocyanate (BDI)), a chain extender (1,4-butanediamine (BDA) or 1,4-butanediol (BDO)), and a poly-e-caprolactone (PCL) segment. Four SPU(U)s, LDI–BDA, LDI–BDO, BDI–BDA, and BDI–BDO, were prepared by a standard two-step prepolymer method. Fourier transformed infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle X-ray scattering (SAXS) measurement indicated that the LDI-series SPU(U)s formed weakly aggregated hard segment domains, which readily dissociated under mechanical deformation and heating. The diamine chain extender, BDA, enhanced the stability of the hard segment domains, and the BDA-series SPU(U)s exhibited better mechanical properties than the BDO-series. The LDI-series SPU(U)s have notable biodegradability, and the BDI-based hard segments delayed the degradation rate because of the strongly segregated hard segment.

Enhanced thermal conductivity in immiscible polyimide blend composites with needle-shaped ZnO particles

Novel blend composite films were prepared by mixing two kinds of immiscible polyimides (PIs), one containing sulfur (SD) and one containing fluorine (TF), with needle-shaped zinc oxide (n-ZnO) particles. Optical microscopy and cross-sectional SEM images revealed that vertical double percolation (VDP) structures were successfully formed in the PI blend films by spontaneous macro-phase separation. In the VDP structures, each phase is separately aligned along the out-of-plane direction, and the n-ZnO particles were selectively incorporated in the TF-rich phase. These blend composite films exhibited significantly higher thermal conductivity (TC) in the out-of-plane direction than blend composite films containing pyramidal ZnO (p-ZnO) particles. The wide-angle X-ray diffraction (WAXD) results revealed that the n-ZnO particles were more randomly oriented in the blend films than those in homopolymer films, in which the particles were preferentially aligned parallel to the film. The n-ZnO particles confined in the VDP structures and partially oriented along the out-of-plane direction contributed to the enhancement of the out-of-plane TC.

Banana-shaped molecular architecture: Formation of large columns composed of two concentrically enclosed layers

The room-temperature solid phase (X3) of banana-shaped molecules that forms on cooling from the B6 phase is characterized as having an extremely large hexagonal lattice. In this study, we acquired a detailed structure of the X3 phase from synchrotron radiation (SR) micro-beam X-ray and atomic force microscopy (AFM) measurements. Focusing the micro X-ray beam on a single fan-shaped domain, we observed a well-oriented pattern including nine hk0 reflections with spacings of 20–110 A. These can be indexed with a two-dimensional (2-D) hexagonal lattice with an edge length of 126.8 A and incorporating approximately 70 molecules. The hk0 reflections appear in a direction parallel to the long axis of the fan-shaped domain showing that the two-dimensional lattice exists in a plane perpendicular to both the layer and bent direction of the molecules in the preceding B6 phase. An AFM image clearly illustrates the close packing of cylinders with a diameter equal to the hexagonal lattice edge. Further, the electron density map elucidated from the X-ray reflection intensity distribution shows that each cylinder is constructed of two concentrically enclosed layers.

In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts

The change in the crystal structure of polymer-grafted nanoparticles during uniaxial stretching was investigated by simultaneous ultra-small-angle X-ray scattering and stress–strain measurement.

Characteristic smectic structures of main-chain liquid-crystalline polyimides driven by a microphase separation between aromatic imide mesogen and a siloxane spacer

We investigated the phase transition behavior and liquid-crystalline structure for main-chain liquid-crystalline polyimides with aromatic imide cores and alkyl and dimethyl siloxane spacers, BPDA/3SiO4-3F. They formed crystal, smectic C (SC), smectic A (SA), and isotropic phases in order of increasing temperature. The characteristic structures of the SA and SC phases were extracted with wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy measurements. In the SC phase, the mesogenic groups were tilted by approximately 40° to the smectic layer and the unusual quasi two-dimensional structural order exists irrespective of the liquid-like packing of aromatic cores within a layer. On heating, the SC phase transformed into the SA phase with a nature of first-order transition. The resulting SA structure was also unusual. The orientational order parameter was 0.43, which was lower than 0.71 in the SC phase. This indicates that a “de Vries”-type of smectic A is formed in which the mesogenic groups are tilted away from the optic axis, but in azimuthally random directions. The average tilt angle was estimated to be 42°. These characteristics were produced because of the strong segregation effect of the dimethyl siloxane spacer groups with a relatively larger molecular area compared to alkyl chain and aromatic imide cores.

Enhancement of Thermal Diffusivity in Phase-Separated Bismaleimide/Poly(ether imide) Composite Films Containing Needle-Shaped ZnO Particles

Phase-separated polymer blend composite films exhibiting high thermal diffusivity were prepared by blending a soluble polyimide (BPADA-MPD) and a bismaleimide (BMI) with needle-shaped zinc oxide (n-ZnO) particles followed by high-temperature curing at 250 °C. Images recorded with a field-emission scanning electron microscope (FE-SEM) equipped with wavelength-dispersive spectroscopy (WDS) demonstrated that the spontaneously separated phases in the composite films were aligned along the out-of-plane direction, and the n-ZnO particles were selectively incorporated into the BMI phase. The out-of-plane thermal diffusivity of the composite films was significantly higher than those of the previously reported composite films at lower filler contents. Based on wide-angle X-ray diffraction (WAXD) patterns and image analysis, the enhanced thermal diffusivity was attributed to the confinement of the anisotropically shaped particles and their nearly isotropic orientation in one phase of the composite films.

Preparation of High-Density Polymer Brushes with a Multihelical Structure

It is well-known that a mixture of isotactic and syndiotactic polymethyl methacrylate (PMMA) forms a stereocomplex consisting of a multihelical structure in which an isotactic chain is surrounded by a syndiotactic chain. Here, we report the basic structure of the stereocomplex formed when the syndiotactic PMMA chains are tethered to a silicon substrate and form a high-density polymer brush. The influence of geometric confinement was investigated by preparing the high-density polymer brushes on a flat and spherical substrate. In both cases, mixing the untethered isotactic PMMA with the grafted syndiotactic PMMA led to the formation of a stereocomplex with a multihelical structure. Static contact angle measurements showed a hindered surface mobility at the outermost surface of the polymer brush, indicating that the stereocomplex forms a crystalline structure. A syndiotactic polymer brush with substituted fluoroalkyl groups was prepared to increase the contrast for grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements. The GIWAXD results verified that the stereocomplex forms a crystalline structure oriented perpendicular to the substrate with a relatively low degree of orientation.