Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yasushi Okumura Last modified date:2018.07.03

Associate Professor / Nano-organization / Department of Integrated Materials / Institute for Materials Chemistry and Engineering


Papers
1. Yu Narazaki, Hiroya Nishikawa, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Substituent effects of bridged binaphthyl-type chiral dopants on the helical twisting power in dopant-induced chiral liquid crystals, RSC Advances, 10.1039/c7ra12465a, 8, 2, 971-979, 2018.01, A new series of chiral dopants, (R)-6,6′-halogenated (1b-1e, X = F, Cl, Br and I) and -methylated (1f) binaphthyl compounds, were designed and synthesized to create chiral liquid crystals by doping them into an achiral nematic liquid crystal (NLC). The influence of halogen (X = F, Cl, Br and I) and methyl substituent factors, such as steric, polar, and polarizability properties, on the helical twisting power (HTP) and their temperature dependences on the chiral dopants were investigated in two host NLCs with different characteristics, fluorinated JC-1041XX and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The chiral dopants possessing less steric and larger polarizability factors increased the HTP values. The structural similarity and electrostatic arene-arene interactions between the chiral dopants and the NLC molecules also exerted important influences on these values. The temperature dependence of the HTP (HTPt.d.) values also correlated well with the steric and polarizability substituents factors in the two host NLCs. Their correlation coefficients (R2) depended on the molecular structural similarity between the chiral dopant and the NLC..
2. K. Rijeesh, Hiroki Higuchi, Yasushi Okumura, Jun Yamamoto, Hirotsugu Kikuchi, Liquid crystal anchoring transitions and weak anchoring interface formation at surfaces created by uniquely designed acrylate copolymers, Polymer, 10.1016/j.polymer.2016.12.012, 2016.11, Weak anchoring of liquid crystals (LCs) can, in principle, have the potential to provide lower operating voltage systems with an improved electro-optic response. The creation of such a liquid crystal system is an important goal for next-generation displays, including polymer-stabilized blue phases. Herein, we report a new method of weak anchoring for LCs in contact with uniquely designed amorphous side-chain copolymers that feature both mesogenic and non-mesogenic units. The mesogenic pendant enhances the compatibility with the LC molecules, while the non-mesogenic part reduces the possible azimuthal anchoring energy of the mesogenic side-chain on LCs. The copolymers with mesogenic pendants bearing polar and non-polar end groups favor planar and homeotropic alignments, respectively. Interestingly, LCs in a glass plate cell coated with these side-chain non-liquid crystalline copolymers showed anchoring transitions and weak anchoring interface formation at precise temperatures. The weak anchoring nature of LCs on copolymer surfaces was confirmed by their easy response to an applied magnetic field. These results suggest that the copolymers perform an important function as weak anchoring surfaces for nematic LCs..
3. K. Rijeesh, Hiroki Higuchi, Yasushi Okumura, Jun Yamamoto, Hirotsugu Kikuchi, Liquid crystal anchoring transitions and weak anchoring interface formation at surfaces created by uniquely designed acrylate copolymers, Polymer, 10.1016/j.polymer.2016.12.012, 2016.11, Weak anchoring of liquid crystals (LCs) can, in principle, have the potential to provide lower operating voltage systems with an improved electro-optic response. The creation of such a liquid crystal system is an important goal for next-generation displays, including polymer-stabilized blue phases. Herein, we report a new method of weak anchoring for LCs in contact with uniquely designed amorphous side-chain copolymers that feature both mesogenic and non-mesogenic units. The mesogenic pendant enhances the compatibility with the LC molecules, while the non-mesogenic part reduces the possible azimuthal anchoring energy of the mesogenic side-chain on LCs. The copolymers with mesogenic pendants bearing polar and non-polar end groups favor planar and homeotropic alignments, respectively. Interestingly, LCs in a glass plate cell coated with these side-chain non-liquid crystalline copolymers showed anchoring transitions and weak anchoring interface formation at precise temperatures. The weak anchoring nature of LCs on copolymer surfaces was confirmed by their easy response to an applied magnetic field. These results suggest that the copolymers perform an important function as weak anchoring surfaces for nematic LCs..
4. Hirotsugu Kikuchi, Hiroki Higuchi, Yasushi Okumura, Kenji Higashiguchi, Interaction between topological defects of liquid crystals and polymers, Kobunshi, 64, 11, 721-726, 2015.11, Around the topological defects of a liquid crystal, there are gradients of the director distortions and the orientational order, where a long range elastic force field is created. When polymers are placed in the field, an attractive force along the gradient, toward the defect core, is imposed to the particles. By this long-range force, the particles are migrated and finally trapped by the defect. The polymer-stabilized liquid crystal blue phases, which show fast electro-optic effect are stabilized by this kind of effect. Recent research progresses on the related phenomena are briefly reviewed in this paper..
5. K. Rijeesh, Hiroki Higuchi, Yasushi Okumura, Jun Yamamoto, Hirotsugu Kikuchi, Liquid crystal anchoring transitions and weak anchoring interface formation at surfaces created by uniquely designed acrylate copolymers, Polymer, 10.1016/j.polymer.2016.12.012, 2016.11, Weak anchoring of liquid crystals (LCs) can, in principle, have the potential to provide lower operating voltage systems with an improved electro-optic response. The creation of such a liquid crystal system is an important goal for next-generation displays, including polymer-stabilized blue phases. Herein, we report a new method of weak anchoring for LCs in contact with uniquely designed amorphous side-chain copolymers that feature both mesogenic and non-mesogenic units. The mesogenic pendant enhances the compatibility with the LC molecules, while the non-mesogenic part reduces the possible azimuthal anchoring energy of the mesogenic side-chain on LCs. The copolymers with mesogenic pendants bearing polar and non-polar end groups favor planar and homeotropic alignments, respectively. Interestingly, LCs in a glass plate cell coated with these side-chain non-liquid crystalline copolymers showed anchoring transitions and weak anchoring interface formation at precise temperatures. The weak anchoring nature of LCs on copolymer surfaces was confirmed by their easy response to an applied magnetic field. These results suggest that the copolymers perform an important function as weak anchoring surfaces for nematic LCs..
6. Rijeesh Kizhakidathazhath, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Weak Anchoring Interface Inducing Acrylate Copolymer Designs for High-Performance Polymer-Stabilized Blue Phase Liquid Crystal Displays, ChemistrySelect, 10.1002/slct.201701233, 2, 23, 6728-6731, 2017.01, Polymer-stabilized blue phase liquid crystal (PS-BPLC) is emerging as a strong competitor for next-generation liquid crystal displays and optoelectronic devices. However, the realization of technologies built on PS-BPLC requires lowering of driving voltage without sacrificing other desirable properties of blue phase liquid crystals. Here, we present a new method for voltage reduction in PS-BPLC based on the stabilization of BPLC with weak anchoring interface inducing acrylate monomers. This method provides significant voltage reduction while maintaining the electro-optical performance of BPLCs at the same time. We believe that this approach has a great potential in developing high-performance photonic devices and displays based on liquid crystals..
7. Hiroya Nishikawa, Kazuya Shiroshita, Hiroki Higuchi, Yasushi Okumura, Yasuhiro Haseba, Shin Ichi Yamamoto, Koki Sago, Hirotsugu Kikuchi, A Fluid Liquid-Crystal Material with Highly Polar Order, Advanced Materials, 10.1002/adma.201702354, 29, 43, 2017.11, An anomalously large dielectric permittivity of ≈104 is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid-crystal compound having a 1,3-dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X-ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 µC cm−2, and a parallelogram-shaped polarization–electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field-induced polarization switching occurs. Furthermore, sufficiently larger second-harmonic generation is observed for DIO in the MP phase. Second-harmonic-generation interferometry clearly shows that the sense of polarization is inverted when the +/− sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric-like parallel polar arrangement of the molecules is generated along the director in the MP phase..
8. Hiroya Nishikawa, Daigou Mochizuki, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Reversible Broad-Spectrum Control of Selective Reflections of Chiral Nematic Phases by Closed-/Open-Type Axially Chiral Azo Dopants, ChemistryOpen, 10.1002/open.201700170, 6, 6, 2017.12, Invited for this month's cover picture is the groups of Professor Hirotsugu Kikuchi and Dr. Yasushi Okumura at the Institute for Materials Chemistry and Engineering at Kyushu University (Japan). External dynamic control of molecular self-organized superstructures with unique features has been researched, as these structures are applicable to chiral molecular devices. The cover picture shows photocontrol of selective reflection color that originated from the self-organized helical structure of chiral nematic liquid crystals (N*LCs) using closed-/open-type dopants. The drastic structure changes of the dopants by light stimuli enable reversible broad-spectrum control of selective reflections of N*LCs with opposite helical sign. Read the full text of the Full Paper at 10.1002/open.201700121..
9. Hiroya Nishikawa, Daigou Mochizuki, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Reversible Broad-Spectrum Control of Selective Reflections of Chiral Nematic Phases by Closed-/Open-Type Axially Chiral Azo Dopants, ChemistryOpen, 10.1002/open.201700121, 6, 6, 710-720, 2017.12, We demonstrate reversible RGB-color photocontrol of a chiral nematic liquid crystal (N*LC) by using newly synthesized closed- and open-type chiral dopants. The photoswitching elements in the dopants are azobenzene units on axially chiral binaphthyl cores. Owing to cis–trans photoisomerization of the azobenzene units, both closed- and open-type compounds showed higher solubility, larger helical twisting power (HTP), and larger changes in HTP than conventional chiral dopants in host LCs. Thus, even at very low dopant concentrations, we successfully controlled the chirality of the induced helical structure of the N*LCs. Consequently, the N*LCs reflected right- and left-handed circularly polarized light (CPL) under a light stimulus. In the N*LCs with closed-type chiral dopants, the RGB-color reflection was reversibly controlled within several seconds. Interestingly, the open-type chiral dopant reversibly inverted CPL with opposite handedness in the near and short-wave IR regions. These novel materials are expected to realize new applications and perspectives in color information and similar technologies..
10. Yu Narazaki, Hiroya Nishikawa, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Substituent effects of bridged binaphthyl-type chiral dopants on the helical twisting power in dopant-induced chiral liquid crystals, RSC Advances, 10.1039/c7ra12465a, 8, 2, 971-979, 2018.01, A new series of chiral dopants, (R)-6,6′-halogenated (1b-1e, X = F, Cl, Br and I) and -methylated (1f) binaphthyl compounds, were designed and synthesized to create chiral liquid crystals by doping them into an achiral nematic liquid crystal (NLC). The influence of halogen (X = F, Cl, Br and I) and methyl substituent factors, such as steric, polar, and polarizability properties, on the helical twisting power (HTP) and their temperature dependences on the chiral dopants were investigated in two host NLCs with different characteristics, fluorinated JC-1041XX and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The chiral dopants possessing less steric and larger polarizability factors increased the HTP values. The structural similarity and electrostatic arene-arene interactions between the chiral dopants and the NLC molecules also exerted important influences on these values. The temperature dependence of the HTP (HTPt.d.) values also correlated well with the steric and polarizability substituents factors in the two host NLCs. Their correlation coefficients (R2) depended on the molecular structural similarity between the chiral dopant and the NLC..
11. Junichi Fukuda, Yasushi Okumura, Hirotsugu Kikuchi, Numerical calculation of Kossel diagrams of cholesteric blue phases, 2018 Emerging Liquid Crystal Technologies XIII Emerging Liquid Crystal Technologies XIII, 10.1117/12.2286290, 10555, 2018.01, Kossel diagrams visualize the directions of strong Bragg reflections from a specimen with periodic ordering. They have played a pivotal role in the determination of the symmetry of cholesteric blue phases, and in the investigation of their structural changes under an electric field. In this work, we present direct numerical calculations of the Kossel diagrams of cholesteric blue phases by solving the Maxwell equations for the transmission and reflection of light incident upon a finite-thickness blue phase cell. Calculated Kossel diagrams are in good agreement with what is expected as a result of Bragg reflections, although some differences are present..
12. Rijeesh Kizhakidathazhath, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Effect of polymer backbone flexibility on blue phase liquid crystal stabilization, Journal of Molecular Liquids, 10.1016/j.molliq.2018.04.085, 262, 175-179, 2018.07, In this study, we synthesized two novel monofunctional acrylate monomers A0DA and A3DA featuring a benzene core and a dodecyl tail, and then investigated their effect on blue phase liquid crystal (BPLC) stabilization. The benzene core is directly linked to the acrylate unit in A0DA, which forms a rigid polymeric backbone. Whereas in A3DA,a propyl spacer is employed to separate the benzene unit from the acrylate group, thereby allowing backbone mobility. By using A0DA as a monofunctional monomer in the BPLC precursor composite, stabilization of BPLC was not seen upon photopolymerization. Interestingly, the use of A3DA showed successful stabilization of BPI lattice structure after polymerization. These results confirm that the origin of stabilization effect of blue phase is the flexibility of A3DA backbone employed; therefore, the polymeric backbone flexibility is suggested to have a major influence on BP stabilization process. Furthermore, we demonstrated a low voltage electro-optical switching of PS-BPLC built on A3DA, while preserving other desirable properties of BPLC. The present study provides useful insight into monomer designs towards BPLC stabilization and enhancement of electro-optical performance..
13. Atsuomi Shundo, Koichiro Hori, Penaloza David P., Jr., Matsumoto Yuji, Yasushi Okumura, Hirotsugu Kikuchi , Kyung Eun Lee, Sang Ouk Kim, Keiji Tanaka, Hierarchical spatial heterogeneity in liquid crystals composed of graphene oxides, PHYSICAL CHEMISTRY CHEMICAL PHYSICS , 2016.08.
14. Akinori Bando, Rumiko Kasahara, Kentaro Kayashima, Yasushi Okumura, Kazuaki Kato, Yasuhiro Sakai, Hideaki Yokoyama, Yuya Shinohara, Yoshiyuki Amemiya, Kohzo Ito, Volume Phase Transitions of Slide-Ring Gels, POLYMERS, 10.3390/polym8060217, 8, 6, 2016.05.
15. Jun-ichi Fukuda, Yasushi Okumura, Hirotsugu Kikuchi , Calculation of confocal microscope images of cholesteric blue phases, EMERGING LIQUID CRYSTAL TECHNOLOGIES XI, 10.1117/12.2209210, 9769, 2016.02.
16. Gihwan Lim, Yasushi Okumura, Hiroki Higuchi, Hirotsugu Kikuchi, Low Temperature Properties of Polymer-Stabilized Liquid Crystal Blue Phases, Materials Research Express, 15, 7, 1447-1451, 2014.05.
17. Fangjie Zhu, Tatsuya Nishimura, Takeshi Sakamoto, Hidekazu Tomono, Hiroki Nada, Yasushi Okumura, Hirotsugu Kikuchi, Takashi Kato, Tuning the Stability of CaCO3 Crystals with Magnesium Ions for the Formation of Aragonite Thin Films on Organic Polymer Templates, Chemistry - An Asian Journal, 2013.09.
18. Shin-ichi Yamamoto, Yasuhiro Haseba, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Lattice plane control of liquid crystal blue phase, Liquid Crystals, 40, 5, 639-645, 2013.06.
19. Seishi Shibayama, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Dendron-Stabilized Liquid Crystalline Blue Phases with an Enlarged Controllable Range of the Photonic Band for Tunable Photonic Devices, Advanced Functional Materials, 23, 19, 2387-2396, 2013.05.
20. Shuhei Yabu, Hiroyuki Yoshida, Gihwan Lim, Kosuke Kaneko, Yasushi Okumura, Noboru Uehara, Hirotsugu Kikuchi, Masanori Ozaki, Dual Frequency Operation of a Blue Phase Liquid Crystal, Optical Materials Express, 1, 8, 1577-1584, 2011.12.
21. Tatsuro Mizunuma, Thet Naing Oo, Yasutomo Nagano, Hengyi Ma, Yasuhiro Haseba, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Electro-Optical Properties of Polymer-Stabilized Blue Phase with Different Monomer Combination and Concentration, Optical Materials Express, 1, 8, 1561-1568, 2011.12.
22. Thet Naing Oo, Tatsuro Mizunuma, Yasutomo Nagano, Hengyi Ma, Yukiko Ogawa, Yasuhiro Haseba, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Effects of Monomer/Liquid Crystal Compositions on Electro-Optical Properties of Polymer-Stabilized Blue Phase Liquid Crystal, Optical Materials Express, 1, 8, 1502-1510, 2011.12.
23. Kota Kakisaka, Hiroki Higuchi, Yasushi Okumura, Hirotsugu Kikuchi, Chiral Liquid Crystalline Phase of Fluorinated Nematic Liquid Crystal Material Doped with a Fluorinated Binaphthyl Chiral Dopant, Proceedings of the 13th Cross Straits Symposium on Materials, Energy and Environmental Engineering, 241-242, 2011.11.
24. Taura, D., Hashidzume, A., Okumura, Y.; Harada, A., Cooperative Complexation of alpha-Cyclodextrin with Alternating Copolymers of Sodium Maleate and Dodecyl Vinyl Ether with Varying Molecular Weights., Macromolecules, 41 (10), 3640-3645., 2008.05.
25. Inoue, Y., Kuad, P., Okumura, Y., Takashima, Y., Yamaguchi, H., Harada, A., Thermal and Photochemical Switching of Conformation of Poly(ethylene glycol)-Substituted Cyclodextrin with an Azobenzene Group at the Chain End., Journal of the American Chemical Society, 129 (20), 6396-6397., 2007.04.
26. Karino, T., Okumura, Y., Zhao, C. M., Kidowaki, M., Kataoka, T., Ito, K., Shibayama, M., Sol-Gel Transition of Hydrophobically Modified Polyrotaxane., Macromolecules, 39 (26), 9435-9440., 2006.12.
27. Shinohara, Y., Kayashima, K., Okumura, Y., Zhao, C. M., Ito, K., Amemiya, Y., Small-angle x-ray scattering study of the pulley effect of slide-ring gels., Macromolecules, 39 (21), 7386-7391., 2006.09.
28. Karino, T., Shibayama, M., Okumura, Y., Ito, K., SANS study on pulley effect of slide-ring gel., Physica B: Condensed Matter, 385-386(Pt. 1), 807-809., 2006.06.
29. Zhao, C., M., Domon, Y., Okumura, Y., Okabe, S., Shibayama, M., Ito, K., Sliding mode of cyclodextrin in polyrotaxane and slide-ring gel., Journal of Physics-Condensed Matter , 17 (31), S2841-S2846., 2005.08.
30. Karino, T., Okumura, Y., Zhao, C. M., Kataoka, T., Ito, K., Shibayama, M., SANS studies on deformation mechanism of slide-ring gel., Macromolecules , 38 (14), 6161-6167., 2005.08.
31. Ito, K., Shimomura, T., Okumura, Y., Nanostructures formed by combination of nanotube and polymer chain., Macromolecular Symposia, 201, 103-110., 2003.10.
32. Ito K, Okumura Y , Scattering study of topological gel., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 225, U696-U696, part1, 2003.03.
33. Okumura, Y., Ito, K., The polyrotaxane gel: A topological gel by figure-of-eight cross-links., Advanced Materials , 13 (7), 485-487., 2001.04.
34. Saito, M., Shimomura, T., Okumura, Y., Ito, K., Hayakawa, R., Temperature dependence of inclusion-dissociation behavior between molecular nanotubes and linear polymers., Journal of Chemical Physics , 114 (1), 1-3., 2001.01.
35. Okumura, Y., Ito, K., Hayakawa, R., Nishi, T., Self-assembling dendritic supramolecule of molecular nanotubes and starpolymers., Langmuir, 16 (26), 10278-10280., 2000.12.
36. Ikeda, E., Okumura, Y., Shimomura, T., Ito, K., Hayakawa, R., Inclusion behavior between molecular nanotubes and linear polymer chains in aqueous solutions., Journal of Chemical Physics , 112 (9), 4321-4325., 2000.03.
37. Okumura, Y., Ito, K., Hayakawa, R., Theory on inclusion behavior between cyclodextrin molecules and linear polymer chains in solutions., Polymers for Advanced Technologies, 11, 815-819., 2000.11.
38. Okumura, Y., Ito, K., Hayakawa, R., Inclusion-dissociation transition in the complex formation between molecular nanotubes and linear polymer chains in solutions., Physical Review Letters, 80 (22), 5003-5006., 1998.06.
39. Okumura, Y., Ikeda, E., Shimomura, T., Ito, K., Hayakawa, R., Inclusion Complex Formation between Polyethylene Glycol Chains and Molecular Nanotubes in Aqueous Solutions., Reports on Progress in Polymer Physics in Japan, 40, 95-98., 1997.06.