Scope of Research
Orientation control of nano- and micro-scale particles, fibers, crystals, etc. is of great importance in various areas of science and technology. We make use of diamagnetic anisotropy of micro particles to align them and to improve their physical, chemical, and biological properties. Microcrystals, including organic, inorganic, biological, and polymeric microcrystals, can align three-dimensionally in a non-uniformly rotating magnetic field to yield magnetically oriented microcrystal array (MOMA) in which microcrystals are three-dimensionally aligned in a solid matrix. MOMAs exhibit X-ray and neutron diffraction images equivalent to those obtained from a real single crystal. Therefore, MOMA technique can be a third diffraction method coming after single crystal and powder diffraction methods.

Movie1: Magnetic alignment of mechanical pencil leads
Movie2: Magnetic alignment of short nylon fibers (fishing line)

Main Research Topics
(1) Orientation-controlled cellulosic materials
(2) New functional materials by orientation control
(3) Single crystal analysis from a powder sample
(4) Magnetic orientation of crystalline polymers
(5) Utilization of magnetic forces
(6) Soft actuators

(1) Magnetic alignment of cellulose whiskers.
Since cellulose whiskers have negative diamagnetic susceptibility, they align uniaxially under a rotating magnetic field. Photos show the side (left top) and top (right bottom) views of magnetically oriented cellulose whiskers. [Sci. Technol. Adv. Mater., 9, 024212 (2008)]

(2) Three-dimensional alignment of cellulose nanocrystals.
A suspension of cellulose nanocrystals (CNCs) can align three-dimensionally under a non-uniform rotating magnetic field. The achieved alignment is consolidated by photopolymerization of the suspending matrix monomer. Photos show observations by optical microscope with color plate obtained for three orthogonal directions, showing different colors, indicating the 3D alignment of CNCs. [J. Phys.: Conf. Ser. 156, 012002 (2009)]

(3) Magnetic alignment of chiral nematic phase of CNC suspension.
A suspension of CNC forms a chiral nematic phase when concentrated. Its helical axis aligns parallel to the applied field, forming a monodomain. Lines in the photo correspond to helical pitch. [Langmuir, 21, 2034 (2005)]

(4) Chiral nematic film made from CNC suspension.
Evaporating suspending liquid of chiral nematic phase under a magnetic field, we obtain chiral nematic film of CNC which forms a monodomain as shown by a photo (bottom right), while multidomain is obtained without magnetic field (top left). [Sci. Technol. Adv. Mater., 9, 024212 (2008)]
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(5) Orientation distribution of CNC in cellulose whisker investigated by magnetic alignment.
Half-widths of X-ray diffraction of magnetically oriented cellulose whiskers differ depending on their size. The larger is the size, the wider is the half width. From these data, correlation length of CNC orientation in a micro fiber of cellulose is estimated. [Macromolecules, 46, 8957 (2013)]

(6) Evaporation induced alignment of cellulose nanowhiskers.
A composite film in which cellulose nanowhiskers are aligned is fabricated by using the orientation of nanowhiskers at the evaporating front. [Biomacromolecules, 15, 60 (2014)]

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(1) Magnetic alignment of carbon fibers (CFs).
CFs have high thermal conductivity in fiber direction. So, a film in which CFs are aligned perpendicular to the film surface can be a good heat-diffusing material. [Langmuir, 16, 858 (2000)]

(2) Diffusion type polarizer.
A film, in which microcrystals are uniaxially aligned works as diffusion type polarizer, if one of the refractive indices of microcrystal coincides with the matrix transparent polymer. Combination of urea crystal and PEMA satisfies the above condition. Magnetic alignment is used to align urea microcrystals. [Polymer Prep. Jpn, 51, 726 (2002)]
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(3) Magnetic alignment of pigments.
By controlling the orientation distribution of pigments, different colors show up when viewed from different angles. [日本印刷学会誌, 45, 27 (2008)]
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(1) 3D alignment of biaxial microcrystals.
Biaxial crystals (triclinic, monoclinic, orthorhombic) align three-dimensionally under a non-uniform rotating magnetic field. By consolidating the alignment we obtain a composite in which microcrystals are aligned three-dimensionally. We call this composite 3D MOMA (Magnetically Oriented Microcrystal Array). A 3D MOMA produces diffraction images equivalent to those from a real single crystal. [Langmuir, 21, 4805 (2005)]
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(2) X-ray diffraction from MOMA.
The figure shows X-ray diffraction image of an L-alanine MOMA, showing well-separated spots. [Langmuir, 22, 3464 (2006)] By using the MOMA, it is possible to solve the structure. [Cryst. Eng. Comm., 16, 6630 (2014)]
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(3) Single crystal NMR analysis via MOMA.
Since a MOMA is similar to a single crystal, it can be used as a sample for single crystal NMR. In fact, using an L-alanine MOMA, we determined the chemical shift tensor (including principal axes and principal values) of carboxyl carbon of L-alanine. [J. Magn. Reson., 223, 68 (2012)]
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(4) In-situ X-ray measurement of Magnetically Oriented Microcrystal Suspension (MOMS).
Magnetically oriented microcrystal suspension is subjected to X-ray diffraction measurement using an apparatus schematically shown in the figure attached to a conventional X-ray diffractometer to obtain diffraction spots. [Cryst. Growth Des., 11, 945 (2011)]
(5) In-situ X-ray diffraction images of 1D MOMS.
1D MOMS (uniaxially magnetically oriented microcrystal suspension) diffraction images of L-alanine measured under static and rotating magnetic fields. [Cryst. Growth Des., 11, 945 (2011)]
(Under Constraction) (6) In-situ X-ray diffraction images of 3D MOMS.
(Under Constraction)

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Crystalline polymers can undergo magnetic orientation during crystallization from a molten state. This phenomenon is common in many crystalline polymers including poly(ethyl terephthalate), isotactic polystyrene, polyethylene, etc. [Polymer J., 35, 823 (2003)]
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(1) Magnetic separation.
Particles receive a force when they are subject to a magnetic field gradient. The intensity of the force depends on the magnetic susceptibility of the particle and hence a mixture of particles is separated. Figure shows the separation of different polymer pellets. [Chem. Lett., 29, 1294 (2000)]
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(2) Magnetic micro patterning of particles.
Under a patterned magnetic field gradient, diamagnetic particles are trapped to the place where the field strength takes minima. Figures show the patterning of mouse osteoblast cells.
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(3) Micro Moses effect.
Under magnetic field gradient, a surface of liquid(s) is deformed.
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A strip of silicone rubber in which miro iron wires are oriented with distribution undergoes bending deformation under an applied magnetic field. [Carbon, 48(14), 4015-4018 (2010), Soft Matter, 8, 6206 (2012)]
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