| 1. |
Sota Inoue, Yasuyuki Kimura and Yuki Uematsu, Ostwald ripening of aqueous microbubble solutions, The Journal of Chemical Physics, https://doi.org/10.1063/5.0128696, 157, 24, 244704-1-244704-10, 2022.12. |
| 2. |
Keita Saito and Yasuyuki Kimura, Optically driven liquid crystal droplet rotator, Scientific Reports, https://doi.org/10.1038/s41598-022-21146-y, 12, 16623-1-16623-8, 2022.10. |
| 3. |
Tomohiro G. Noguchi, Yasutaka Iwashita and Yasuyuki Kimura, Controlled armoring of metal surfaces with metallodielectric patchy particles, The Journal of Chemical Physics, 10.1063/1.5090440, 150, 17, 174903-1-174903-8, 2019.04. |
| 4. |
Toyokazu Ikeda, Haruka Eitoku and Yasuyuki Kimura, AC electrophoretic mobility of individual microscale colloidal particles measured using holographic video microscopy
, Applied Physics Letters, 10.1063/1.5088723, 114, 15, 153703-1-153703-4, 2019.04. |
| 5. |
Ryotaro Koike, Yasutaka Iwashita, Yasuyuki Kimura, Emulsion Droplets Stabilized by Close-Packed Janus Regular Polygonal Particles, Langmuir, 10.1021/acs.langmuir.8b02323, 34, 41, 12394-12400, 2018.10, In Pickering-Ramsden emulsions, the packing structure of the colloidal particles at the liquid-liquid (or liquid-gas) interface significantly affects the structure and behavior of the emulsion. Here, using a series of platelike particles with regular polygonal shapes and Janus amphiphilicity, we created emulsion droplets stabilized by close-packed polygonal particles at the interface. The systematic variation of the particle morphology shows that the geometrical features of the regular polygons in (curved) planar packing dominate over the self-assembled structures. The structures are tessellations of triangular, square, and hexagonal particles at the surface for large droplets and regular tetrahedral, cubic, and dodecahedral particle shells of triangular, square, and pentagonal particles for small droplets, respectively. This work creates the possibility of geometrically designing the structure and functionality of emulsions.. |
| 6. |
Mariko Suga, Saori Suda, Masatoshi Ichikawa, Yasuyuki Kimura, Self-propelled motion switching in nematic liquid crystal droplets in aqueous surfactant solutions, Physical Review E, 10.1103/PhysRevE.97.062703, 97, 6, 2018.06, The self-propelled motions of micron-sized nematic liquid crystal droplets in an aqueous surfactant solution have been studied by tracking individual droplets over long time periods. Switching between self-propelled modes is observed as the droplet size decreases at a nearly constant dissolution rate: from random to helical and then straight motion. The velocity of the droplet decreases with its size for straight and helical motions but is independent of size for random motion. The switching between helical and straight motions is found to be governed by the self-propelled velocity, and is confirmed by experiments at various surfactant concentrations. The helical motion appears along with a shifting of a point defect from the self-propelled direction of the droplet. The critical velocity for this shift of the defect position is found to be related with the Ericksen number, which is defined by the ratio of the viscous and elastic stresses. In a thin cell whose thickness is smaller than that of the initial droplet size, the droplets show more complex trajectories, including "figure-8s" and zigzags. The appearance of those characteristic motions is attributed to autochemotaxis of the droplet.. |
| 7. |
Keita Saito, Shogo Okubo, Yasuyuki Kimura, Change in collective motion of colloidal particles driven by an optical vortex with driving force and spatial confinement, Soft Matter, 10.1039/c8sm00582f, 14, 29, 6037-6042, 2018.01, We studied the change in collective behavior of optically driven colloidal particles on a circular path. The particles are simultaneously driven by the orbital angular momentum of an optical vortex beam generated by holographic optical tweezers. The driving force is controlled by the topological charge l of the vortex. By varying the driving force and spatial confinement, four characteristic collective motions were observed. The collective behavior results from the interplay between the optical interaction, hydrodynamic interaction and spatial confinement. Varying the topological charge of an optical vortex not only induces changes in driving force but also alters the stability of three-dimensional optical trapping. The switch between dynamic clustering and stable clustering was observed in this manner. Decreasing the cell thickness diminishes the velocity of the respective particles and increases the spatial confinement. A jamming-like characteristic collective motion appears when the thickness is small and the topological charge is large. In this regime, a ring of equally-spaced doublets was spontaneously formed in systems composed of an even number of particles.. |
| 8. |
Yasuyuki Kimura, Hydrodynamically induced collective motion of optically driven colloidal particles on a circular path, Journal of the Physical Society of Japan, 10.7566/JPSJ.86.101003, 86, 10, 2017.10, Among typical active matter such as self-propelled micro-objects, the characteristic collective motion originating from the hydrodynamic interaction between constituents has been observed in both biological and artificial systems. In illustrating such motion of micrometer-size particles in a one-dimensional optically driven system with a low Reynolds number, we highlight the importance of the hydrodynamic interaction. We show the appearance of regular stationary and dynamic arrangements resembling “crystals” or “clusters” observed in the equilibrium state. A transition in the collective motion has been observed by varying the hydrodynamic interaction in a system of two particle sizes and in a spatially confined system. An optical manipulation technique and the related hydrodynamic equations are also discussed. These are useful tools for elucidating the complex collective behavior of the hydrodynamically coupled micro-objects.. |
| 9. |
Yasutaka Iwashita, Yasuyuki Kimura, Density dependence of orientational order in one-patch particles, Soft Matter, 10.1039/c7sm00565b, 13, 29, 4997-5007, 2017.06, Closely packed spherical patchy particles exhibit a range of orientationally ordered equilibrium structures depending on patch size and particle arrangement due to the existence of a sticky inter-patch interaction and rotational degrees of freedom. We experimentally study the packing density dependence of such ordering in particles with a thin deposited patch which imparts a shape anisotropy of a few percent in aspect ratio. These are confined between flat substrates with a chamber thickness of up to two particle layers. When the particles are tightly packed and almost in contact with each other, the anisotropic hard-body interaction dictates the orientational order. Thus, the order depends little on patch size, with rotational motion almost frozen. A small decrease in the density allows free rotational motion while translation is restricted to vibrational motion. This drastically changes the ordering mechanism, giving rise to a patch-size dependent equilibrium orientational order. Furthermore, within this density regime, we find yet another density-dependent transition within the tetragonal bilayer. This transition is reproduced by numerical simulation assuming no shape anisotropy, indicating that shape anisotropy is unnecessary for the transition and translational entropy significantly affects the equilibrium orientational order even in such a closely packed structure. Our study demonstrates the sensitivity of the ordering mechanism and the resulting order to the packing density, where the effect of such a tiny shape anisotropy is clearly observable owing to the patch opacity. The dependence of cluster structure in particle dispersions on patch size, confinement thickness and packing density is also reported.. |
| 10. |
Tomohiro G Noguchi, Yasutaka Iwashtia, Yasuyuki Kimura, Dependence of the internal structure on water/particle volume ratio in an amphiphilic Janus
particle–water–oil ternary system: from micelle-like clusters to emulsions of spherical
droplets, Langmuir, 33, 1030-1036, 2017.01. |
| 11. |
田村優太, Yasuyuki Kimura, Two-dimensional assemblies of nematic colloids in homeotropic cells and their response to
electric fields, Soft Matter, 12, 6817-6826 , 2016.09. |
| 12. |
Yasutaka Iwashtia, Yasuyuki Kimura, Spatial confinement governs orientational order in patchy particles, Scientific reports, 6, 27599-1-27599-8, 2016.05. |
| 13. |
Yasuyuki Kimura, Shogo Okubo, Dynamic clustering of driven colloidal particles on a circular path, PHYSICAL REVIEW E, 10.1103/PhysRevE.92.032303, 92, 3, 2015.09. |
| 14. |
田中小百合, 沖佑馬, 木村 康之, Melting of a finite-sized two-dimensional colloidal crystal, Physical Review E, 10.1103/PhysRevE.89.052305, 89, 052305-1-052305-9, 2014.05, 有限サイズの２次元コロイド結晶の融解過程をビデオマイクロスコピーにより調べた。局所的な面積密度φとヘキサチック秩序ψ6を各ボロノイセルに対して求めた。結晶（クラスター）の中心からの距離の関数としてφと|ψ6|を求め、その時間変化を調べた。その結果、φはクラスター中ではほぼ一定の値を示し、その値が時間とともに単調に減少することがわかった。一方、|ψ6(r)|は初期過程では|ψ6| = 1の核が存在するが、その後、ｒの単調減少関数となることがわかった。さらに、ソフトコア粒子を用いた有限サイズ結晶の融解過程をブラウンダイナミクスシミュレーションを用いて調べ、融解過程における有限サイズ効果を確かめた。また、得られた結果は定性的に実験とよい一致をみた。. |
| 15. |
Yasuyuki Kimura, Kuniyoshi Izaki, Hydrodynamic effects in the measurement of interparticle forces in nematic colloids, PHYSICAL REVIEW E, 10.1103/PhysRevE.88.054501, 88, 5, 2013.11. |
| 16. |
Yasuyuki Kimura, yasutaka iwashtia, Stable cluster phase of Janus particles in two dimensions, Soft Matter, 10.1039/c3sm52146j, 9, 5, 2013.09. |
| 17. |
Yasuyuki Kimura, Kuniyoshi Izaki, Interparticle force between different types of nematic colloids, PHYSICAL REVIEW E, 10.1103/PhysRevE.87.062507, 87, 6, 2013.06. |
| 18. |
Yasuyuki Kimura, Takahiro Kishita, Kosuke Kita, Moboru Kondo, Nematic colloids - interaction between particles in anisotropic liquids , Journal of the Physical Society of Japana, 10.1143/JPSJS.81SA.SA007, 81, A, SA007-1-SA007-8, 2012.09. |
| 19. |
Yuriko Sassa, Shuhei Shibata, yasutaka iwashtia, Yasuyuki Kimura, Hydrodynamically induced rhythmic motion of optically driven colloidal particles on a ring, PHYSICAL REVIEW E, 10.1103/PhysRevE.85.061402, 85, 6, 2012.06. |
| 20. |
Takahiro Kishita, Noboru Kondo, Kenji Takahashi, Masatoshi Ichikawa, Jun-ichi Fukuda and Yasuyuki Kimura, Interparticle force in nematic colloids - comparison between experiment and theory , Physical Review E, 10.1103/PhysRevE.84.021704, 84, 2, 021704-1-9, 2011.08. |
| 21. |
Naoki Yamamoto, Masatoshi Ichikawa, and Yasuyuki Kimura, Local mechanical properties of a hyperswollen lyotropic lamellar phase, Physical Review E, 82, 2, 021506-1~-8, 2010.08. |
| 22. |
Hitoshi Uemura, Masatoshi Ichikawa, and Yasuyuki Kimura, Crossover behavior in static and dynamic properties of a single DNA molecule from three to quasi-two dimensions
, Physical Review E, 81, 5, 051801-1～-7, 2010.05. |
| 23. |
Takahiro Kishita, Kenji Takahashi, Masatoshi Ichikawa, Jun-ichi Fukuda and Yasuyuki
Kimura, Arrangement dependence of interparticle force in nematic colloids, Physical Review E, 81, 1, 010701-1～-4, 2010.01. |
| 24. |
Yoko Shitamichi, Masatoshi Ichikawa and Yasuyuki Kimura, Mechanical properties of a giant liposome studied using optical tweezers, Chemical Physics Letters, 479, pp.274-278
, 2009.09. |
| 25. |
Yusuke Yoshida and Yasuyuki Kimura, Synchronization of Two Target Patterns, Journal of Physical Society of Japan, 78, pp.084801-1～-4, 2009.08. |
| 26. |
Yasuyuki Kimura, Microrheology of Soft Matter, Journal of Physical Soceity of Japan, Vol.78, No.4, p.041005-1～-8, 2009.04. |
| 27. |
Kosuke Kita, Masatoshi Ichikawa and Yasuyuki Kimura, Self-Assembly of Polymer Droplets in Nematic Liquid Crystal at Phase Separation, Physical Review E, vol. 77, pp.041702-1～-4, 2008.04. |
| 28. |
Kenji Takahashi, Masatoshi Ichikawa and Yasuyuki Kimura, Direct measurement of force between colloidal particles in nematic liquid crystal, Journal of Physics: Condensed Matter, vol.20, 075106-1～-5.
, 2008.02. |
| 29. |
Kenji Takahashi, Masatoshi Ichikawa and Yasuyuki Kimura, Novel force between colloidal particles in a nematic liquid crystal studied by optical tweezers, Physical Review E, vol.77, pp.020703(R)-1～-4.
, 2008.02. |
| 30. |
Masatoshi Ichikawa, Koji Kubo, Kenichi Yoshikawa and Yasuyuki Kimura, Tilt control in optical tweezers, Journal of Biomedical Optics, vol. 13 (1), pp.010503-1～-3, 2008.02. |
| 31. |
Yasuyuki Kimura and Daisuke Mizuno, Microrheology of a swollen lyotropic lamellar phase, Molecular Crystals and Liquid Crystals, vol.478, pp.3-13.
, 2007.12. |
| 32. |
M. Ichikawa, H. Ichikawa, K. Yoshikawa and Y. Kimura, Extension of a DNA Molecule by Local Heating with a Laser, Physical Review Letters, 99 (14), pp.148104, 2007.09. |
| 33. |
Y. Kimura, T. Mori, A. Yamamoto and D. Mizuno, Hierarchical transport of nano-particles in lyotropic lamellar phase, Journal of Physics: condensed matter, 10.1088/0953-8984/17/31/021, 17, 31, S2937-S2942, vol.17, pp. S2937-2942, 2005.07. |
| 34. |
D. Mizuno, Y. Kimura and R. Hayakawa, Electrophoretic microrheology of a dilute lamellar phase: Relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes, Physcal Review E, vol 70, 011509-1-17, 2004.07. |
