Recent research interests

• Liquid crystal colloids

  As shown in a seminal work by Poulin and co-workers [1], a spherical particle in a uniformly aligned nematic liquid crystal can accompany a point-like hedgehog defect and that such particles interact with each other via the deformation of the host nematic to form a linear chain. To reproduce a hedgehog defect accompanying a colloidal particle in computer simulations is, however, highly challenging because of the large difference between the size of colloidal particle (typically microns) and the nematic coherence length characterizing the defect core size (of the order of 10nm).

  By devising a numerical scheme with an adaptive mesh refinement technique [2], Fukuda successfully overcame the above-mentioned difficulty arising from the multi-scale nature of the problem to obtain a stable hedgehog defect in his simulations and discuss its energetics in comparison with a different configuration, a "Saturn ring" defect encircling a particle. He also reproduced [3] the transition from a hedgehog to a Saturn ring under an electric field that had been observed experimentally [4]. Moreover, he made a first accurate calculation of the interaction force between two particles carrying a hedgehog [5], which stimulated experimental studies to confirm his findings [6]. He also successfully explained [7] an unusual attractive interaction mediated by a "bubble-gum" defect observed experimentally [8]. Furthermore, he investigated, with Holger Stark (now at Technische Universität Berlin), how a colloidal particle immersed in an isotropic phase of a liquid crystal is wetted by a nematic phase [9], and how a condensed nematic phase mediates a capillary force between two colloidal particles [10].

  His activities were not confined to numerical work, and his analytical studies gave a first rigorous account for the interaction between particles in a thin cell [11], which beautifully explained experimental findings [12].

  His work is not only a pioneering theoretical study to understand the basic features of liquid crystal colloids, but also one of the first studies that tackled the multi-scale nature of soft materials directly. His achievements in the field of liquid crystal colloids, together with the then-current status of this field, are reviewed in [13].

  Most of his work concerning liquid crystal colloids was carried out with Hiroshi Yokoyama (now at Liquid Crystal Institute, Kent State University) and Makoto Yoneya (now at National Institute of Advanced Industrial Science and Technology (AIST) ) while he was in Yokoyama Nano-structured Liquid Crystal Project, JST, or National Institute of Advanced Industrial Science and Technology (AIST).

  1. P. Poulin, H. Stark, T. C. Lubensky, and D. A. Weitz, Science 275, 1770-1773 (1997).
  2. J. Fukuda and H. Yokoyama, "Director configuration and dynamics of a nematic liquid crystal around a two-dimensional spherical particle: Numerical analysis using adaptive grids" Eur. Phys. J. E 4, 389-396 (2001);
     J. Fukuda, M. Yoneya and H. Yokoyama, "Defect structure of a nematic liquid crystal around a spherical particle: Adaptive mesh refinement approach" Phys. Rev. E 65, 041709 (2002);
     J. Fukuda, M. Yoneya and H. Yokoyama, "Nematic liquid crystal around a spherical particle: Investigation of the defect structure and its stability using adaptive mesh refinement" Eur. Phys. J. E 13, 87-98 (2004).
  3. J. Fukuda, M. Yoneya and H. Yokoyama, "Director configuration of a nematic liquid crystal around a spherical particle: Numerical analysis using adaptive mesh refinement" Mol. Cryst. Liq. Cryst 413, 221-229 (2004);
     J. Fukuda, M. Yoneya and H. Yokoyama, "Stability of the director profile of a nematic liquid crystal around a spherical particle under an external field" Eur. Phys. J. E 21, 341-347 (2006).
  4. J.C. Loudet and P. Poulin, Phys. Rev. Lett. 87, 165503 (2001).
  5. J. Fukuda, M. Yoneya, H. Stark and H. Yokoyama, "Interaction between two spherical particles in a nematic liquid crystal" Phys. Rev. E 69, 041706 (2004);
     J. Fukuda, M. Yoneya, H. Stark and H. Yokoyama, "Interaction between Particles in a Nematic Liquid Crystal: Numerical Study Using the Landau-de Gennes Continuum Theory" Mol. Cryst. Liq. Cryst 435, 723-734 (2004)
  6. K. Takahashi, M. Ichikawa and Y. Kimura, Phys. Rev. E 77, 020703(R) (2008).
  7. J. Fukuda and H. Yokoyama, "Separation-independent attractive force between like-particles mediated by nematic liquid crystal distortions" Phys. Rev. Lett. 94, 148301 (2005).
  8. P. Poulin, V. Cabuil, and D. A. Weitz, Phys. Rev. Lett. 79, 4862-4865 (1997).
  9. J. Fukuda, H. Stark and H. Yokoyama "Wetting of a spherical particle by a nematic liquid crystal" Phys. Rev. E 69, 021714 (2004).
  10. H. Stark, J. Fukuda and H. Yokoyama "Capillary condensation in liquid crystal colloids" Phys. Rev. Lett. 92, 205502 (2004).
  11. J. Fukuda, B.I. Lev and H. Yokoyama, "Effect of confining walls on the interaction between particles in a nematic liquid crystal" J. Phys.: Condensed Matter 15, 3841-3854 (2003);
      J. Fukuda and S. Žumer, "Confinement effect on the interaction between colloidal particles in a nematic liquid crystal: An analytical study" Phys. Rev. E 79, 041703 (2009).
  12. M. Vilfan et al., Phys. Rev. Lett. 101, 237801 (2008).
  13. J. Fukuda, "Liquid Crystal Colloids: A Novel Composite Material Based on Liquid Crystals" J. Phys. Soc. Jpn. 78, 041003 (2009).