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Jun-ichi FUKUDA Last modified date:2022.06.16

Professor / Condensed Matter Physics
Department of Physics
Faculty of Sciences


Graduate School
Undergraduate School


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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/junichi-fukuda
 Reseacher Profiling Tool Kyushu University Pure
https://cmt.phys.kyushu-u.ac.jp/~J.Fukuda/
Academic Degree
Dr. of Science
Country of degree conferring institution (Overseas)
No
Field of Specialization
Condensed Matter Physics, Statistical Physics, Computational Physics
ORCID(Open Researcher and Contributor ID)
0000-0003-3552-8406
Total Priod of education and research career in the foreign country
01years06months
Outline Activities
I study statistical physics and computational physics of soft matter. In particular, I focus on the mechanism and dynamics of self-organized structures of liquid crystals and optical properties of such structures.
Research
Research Interests
  • Statistical and Computational Physics of Soft Condensed Matter
    keyword : Soft Matter, Liquid Crystal, Polymer, Colloid
    1999.04.
Academic Activities
Papers
1. K.Z. Takahashi, T. Aoyagi J. Fukuda, Multi-step nucleation of anisotropic molecules, Nature Communications, https://doi.org/10.1038/s41467-021-25586-4, 12, 5278, 2021.09, [URL], 従来の古典核生成理論において、さまざまな物質のナノ構造は1段階~2段階のプロセスを経て生成されると説明されていた。しかし今回、液晶の場合にはより複雑な3段階のプロセスを経ることを発見するとともに、そのメカニズムの解明にも成功した。本解析技術は液晶だけでなくポリマーや生体材料などさまざまな物質の解析にも応用可能なため、幅広い高機能材料の創製につながる。.
2. Andriy Nych, Jun-ichi Fukuda, Uliana Ognysta, Slobodan Zumer, Igor Musevic, Spontaneous formation and dynamics of half-skyrmions in a chiral liquid-crystal film, NATURE PHYSICS, 10.1038/NPHYS4245, 13, 12, 1215-+, 2017.12, Skyrmions are coreless vortex-like excitations emerging in diverse condensed-matter systems, and real-time observation of their dynamics is still challenging. Here we report the first direct optical observation of the spontaneous formation of half-skyrmions. In a thin film of a chiral liquid crystal, depending on experimental conditions including film thickness, they form a hexagonal lattice whose lattice constant is a few hundred nanometres, or appear as isolated entities with topological defects compensating their charge. These half-skyrmions exhibit intriguing dynamical behaviour driven by thermal fluctuations. Numerical calculations of real-space images successfully corroborate the experimental observations despite the challenge because of the characteristic scale of the structures close to the optical resolution limit. A thin film of a chiral liquid crystal thus offers an intriguing platform that facilitates a direct investigation of the dynamics of topological excitations such as half-skyrmions and their manipulation with optical techniques..
3. H. Yoshida, K. Asakura, J. Fukuda, M. Ozaki, Three-dimensional positioning and control of colloidal objects utilizing engineered liquid crystalline defect networks, NATURE COMMUNICATIONS, 10.1038/ncomms8180, 6, 2015.05, Topological defects in liquid crystals not only affect the optical and rheological properties of the host, but can also act as scaffolds in which to trap nano or micro-sized colloidal objects. The creation of complex defect shapes, however, often involves confining the liquid crystals in curved geometries or adds complex-shaped colloidal objects, which are unsuitable for device applications. Using topologically patterned substrates, here we demonstrate the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality, in a flat slab of nematic liquid crystal. By using the defect lines as templates and the electric response of the liquid crystals, colloidal superstructures are constructed, which can be reversibly reconfigured at a voltage as low as 1.3V. Three-dimensional engineering of the defect shapes in liquid crystals is potentially useful in the fabrication of self-healing composites and in stabilizing artificial frustrated phases..
4. Takuya Ohzono, Takahiro Yamamoto, Jun-ichi Fukuda, A liquid crystalline chirality balance for vapours, NATURE COMMUNICATIONS, 10.1038/ncomms4735, 5, 2014.04, Chiral discrimination of vapours plays an important role in olfactory perception of biological systems and its realization by artificial sensors has been an intriguing challenge. Here, we report a simple method that tangibly visualizes the chirality of a diverse variety of molecules dissolved from vapours with high sensitivity, by making use of a structural change in a periodic microstructure of a nematic liquid crystal confined in open microchannels. This microstructure is accompanied by a topological line defect of a zigzag form with equal lengths of 'zig' and 'zag.' We find that a tiny amount of vapour of chiral molecules injected onto the liquid crystal induces the imbalance of 'zig' and 'zag' depending on its enantiomeric excess within a few seconds. Our liquid- crystal-based 'chirality balance' offers a simple, quick and versatile chirality-sensing/-screening method for gas-phase analysis (for example, for odours, environmental chemicals or drugs)..
5. Takuya Ohzono, Jun-ichi Fukuda, Zigzag line defects and manipulation of colloids in a nematic liquid crystal in microwrinkle grooves, NATURE COMMUNICATIONS, 10.1038/ncomms1709, 3, 2012.02, Spatially confined liquid crystals exhibit non-uniform alignment, often accompanied by self-organised topological defects of non-trivial shape in response to imposed boundary conditions and geometry. Here we show that a nematic liquid crystal, when confined in a sinusoidal microwrinkle groove, exhibits a new periodic arrangement of twist deformations and a zigzag line defect. This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces. The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects. Moreover, the kinks in the zigzag defects can trap small particles, which may afford a new method for manipulation of colloids. Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects..
6. Jun-ichi Fukuda, Slobodan Zumer, Ring Defects in a Strongly Confined Chiral Liquid Crystal, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.106.097801, 106, 9, 2011.03, We find numerically that a regular array of isolated ring defects can exist as a stable state in a highly chiral liquid crystal confined in a thin cell imposing fixed planar anchoring at the parallel confining surfaces. This peculiar defect structure can be stable when the cell thickness d is around 3/4 of the helical pitch p. A cell of thickness 3p/4 with parallel surface anchoring is incompatible with helical alignment that favors d mp/2 (with m being an integer). Formation of ring defects can thus be regarded as a result of frustrations between the helical alignment with a specific pitch and the confining surfaces that prevent it..
7. Jun-ichi Fukuda, Slobodan Zumer, Quasi-two-dimensional Skyrmion lattices in a chiral nematic liquid crystal, NATURE COMMUNICATIONS, 10.1038/ncomms1250, 2, 1, 2011.03, Skyrmions are particle-like topological entities in a continuous field that have an important role in various condensed matter systems, including two-dimensional electron gases exhibiting the quantum Hall effect, chiral ferromagnets and Bose-Einstein condensates. Here we show theoretically, with the aid of numerical methods, that a highly chiral nematic liquid crystal can accommodate a quasi-two-dimensional Skyrmion lattice as a thermodynamically stable state, when it is confined to a thin film between two parallel surfaces imposing normal alignment. A chiral nematic liquid crystal film can thus serve as a model Skyrmion system, allowing direct investigation of their structural properties by a variety of optical techniques at room temperatures that are less demanding than Skyrmion systems discussed previously..
8. Jun-ichi Fukuda, Slobodan Zumer, Novel Defect Structures in a Strongly Confined Liquid-Crystalline Blue Phase, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.104.017801, 104, 1, 2010.01, In our numerical study based on a phenomenological description of strongly confined liquid crystalline blue phase I (BP I), we find several novel structures characterized by specific configurations of topological disclination lines. The thickness of the system is of the order of the dimension of the unit cell of the bulk BP I and the confining surfaces adopts homeotropic anchoring. The structures include an array of double-helix disclination lines accompanied by an orthorhombic lattice of double-twist cylinders, and two parallel arrays of winding disclination lines almost perpendicular to each other..
9. Jun-ichi Fukuda, Makoto Yoneya, Hiroshi Yokoyama, Surface-groove-induced azimuthal anchoring of a nematic liquid crystal: Berreman's model reexamined, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.98.187803, 98, 18, 2007.05, To account for azimuthal surface anchoring of a nematic liquid crystal, Berreman [Phys. Rev. Lett. 28, 1683 (1972)] proposed a simple model attributing the surface anchoring to the elastic distortion of the liquid crystal induced by the grooves of a surface. He showed that the surface anchoring energy is proportional to sin(2)phi, with phi being the angle between the director at infinity and the direction of the surface grooves. We argue that his assumption of negligibly small azimuthal distortion of the nematic is not valid. Proper treatment of the azimuthal distortion reveals that the Berreman's model should yield a surface anchoring energy proportional to sin(4)phi. This implies that surface grooves alone cannot contribute to the surface anchoring coefficient in the usual Rapini-Papoular sense..
10. Junichi Fukuda, Hiroshi Yokoyama, Separation-independent attractive force between like particles mediated by nematic-liquid-crystal distortions, Physical Review Letters, 10.1103/PhysRevLett.94.148301, 94, 14, 2005.04, We investigate numerically with the aid of the Landau-de Gennes continuum theory the interaction between two spherical particles carrying the same topological charges +1 mediated by the elastic distortion of a nematic liquid crystal. We consider the case where an escaped nontopological ring disclination is situated between the particles; the director is continuous everywhere and no counterdefects are present. We find that the interaction is attractive and its potential energy depends linearly on the interparticle distance D. This behavior yields the D-independent interaction force, which was observed experimentally by Poulin, Cabuil, and Weitz [Phys. Rev. Lett. 79, 4862 (1997)] in the presence of narrow strings of birefringent regions ("bubble-gum" configuration) between the particles..
11. Holger Stark, Junichi Fukuda, Hiroshi Yokoyama, Capillary condensation in liquid-crystal colloids, Physical Review Letters, 10.1103/PhysRevLett.92.205502, 92, 20, 2004.05, The capillary condensation between two spherical particles dispersed in the isotropic phase of a nematic liquid crystal was investigated. The interaction energies due to the formation of capillary bridges that reproduce experimental observations were calculated within the Landau-de Gennes theory. The fluctuations in the particle cluster were described by an effective two-state system, close to the critical point of the transition line separating the no-bridge from the bridge configuration. It was found that for the small particles, the transition line vanishes and the shape of interaction potential depends on particle size..
12. Junichi Fukuda, Holger Stark, Makoto Yoneya, Hiroshi Yokoyama, Interaction between two spherical particles in a nematic liquid crystal, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 69, 4 1, 2004.04, The interaction between two spherical particles in a nematic liquid crystal was investigated. The Landau-de Gennes continuum theory was adopted in terms of a second-rank tensor order parameter for the description of the orientational order of a nematic liquid crystal. An adaptive mesh refinement method was used that proves to be an efficient way of dealing with topological defects, whose core size is much smaller than the particle size. It is observed that when the dipoles composed of a particle and a hyperbolic hedgehog defect align in parallel directions, the interaction potential is attractive for large particle separations..
Presentations
1. Jun-ichi FUKUDA, Exotic defect structures of a chiral liquid crystal sandwiched by two parallel substrates and their optical properties, SIAM Conference on Mathematical Aspects of Materials Science 2021 (MS21), 2021.05, [URL].
2. J. Fukuda, Exotic ordered structures of a thin film of a chiral liquid crystal and their optical properties, International Conference on Liquid Crystals, Liquid Crystalline Polymers and Nanosystem, 2019.12.
3. J. Fukuda, Simulation Study on the Self-organized Structures of a Liquid Crystal, National Taiwan Normal UniversityーKyushu University Joint Forum on Facilitating Interdisciplinary Research and Education, 2019.05.
4. J. Fukuda and S. Zumer, Theoretical study on optical properties
of liquid crystalline Skyrmion lattice, SPIE Photonics West "Emerging Liquid Crystal Technologies XIV", 2019.02.
5. J. Fukuda, Exotic mesoscale structures in a thin film of a chiral liquid crystal, Soft Matter Physics: from the perspective of the essential heterogeneity, 2018.12.
6. J. Fukuda, A. Nych, U. Ognysta, S.Zumer, I. Musevic, Half-Skyrmions in a chiral liquid crystal film, The 27th International Liquid Crystal Conference, 2018.07.
Membership in Academic Society
  • The Physical Society of Japan
  • Japanese Liquid Crystal Society
  • The Molecular Simulation Society of Japan
Educational
Other Educational Activities
  • 2022.01.
  • 2021.01.