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義永 那津人


Tel: 03-5841-4183
Fax: 03-5841-4183
E-mail address:
Web page:


I move from 16th Dec. 2011 to Tohoku University
current address:
(new homepage is here)
Mathematics Unit, WPI Advanced Institute for Materials Research (WPI-AIMR),
Tohoku University Katahira 2-1-1, Aoba-Ku,
Sendai 9808577, Japan
Tel: +81-(0)22-217-6327
Fax: +81-(0)22-217- 5129

E-mail address:
Web page:


My research area is the statistical physics of complex soft condensed materials. Soft materials contain various length and time scales, which couple together in a complicated manner. Therefore we do not have one unique method to analyze them. Starting from microscopic (for example atomic) systems is not always efficient. As a result, we need to combine number of methods or sometimes create new ways to find essential route to the reality. The importance of this field is that such systems are closely related to biological phenomena, which give us unlimited imagination and intuition. In addition, they contain most of industrial products, and sustain our comfortable lives.

My interests are how to describe these complicated systems in a simple way. Although these systems contain various time and length scales, most of the scales are slaved by a few slow and mesoscopic variables. This makes problems very clear and tractable. To perform this reduction, physical imaginations is often needed. I use simulations not only for comparison with theories and experiments but also to obtain the imaginations. We employ mainly theoretical (analytical and numerical) methods to study these problems. On the other hand, I am not confined to theoretical methods and I did study with experimental techniques, such as the fluorescent microscopy aThu, 19.01.2012rs are one of representations in soft materials. My research focuses on folding transition of single semiflexible polymers. In the polymer physics, various properties of flexible polymers, which have no bending rigidity, are discussed. On the other hand, the understandings of semiflexible polymers are still developing in spite of the fact that semiflexible polymers have important features of folding into organized structures. This is important because in biological systems, DNA molecules and proteins have well-organized structures and they are closely related with their functions. Therefore we have studied with atomic force microscopy the conformation of DNA molecules, especially long so that we can discuss statistical properties of single molecules. It has been clarified that such long DNA molecules make transitions into folded states with condensing agents, and we therefore investigated the effect of the specific binding with DNA on the folding transition using the intercalating molecules. We have also considered theoretically the phase transition of semiflexible polymers between the elongated coiled state and the folded states, and found that the effect of bending rigidity changes qualitative feature of the transition by coupling of density and orientational order of degree of freedoms.

On the other hand, semiflexible polymers at nonequilibrium state are far less understood even though most of the biological and chemical systems are far from equilibrium. We have studied semiflexible polymers under external mechanical loading and unloading, and folding kinetics of them. We performed simulations of mechanical unfolding and refolding and found that there is large hysteresis in this cycle. These results were analyzed with phenomenological scaling approach and the two-variable model in more general way. The scaling approach was applied for the folding and unfolding kinetics of single semiflexible polymers and compared with simulations.

Transition Kinetics of a single semiflexible polymer We investigate theoretically the kinetics of the folding transition of a single semiflexible polymer. In the folding process, long-axis length of a chain decreases linearly in time. In the unfolding process, dynamic scaling exponents, 1/8 and 1/4, were determined for disentanglement and relaxation processes, respectively.


Polymer stretching Kinetics of conformational change of a semiflexible polymer under mechanical external Field were investigated with Langevin dynamics simulations. It is found that a semiflexible polymer exhibits large hysteresis in mechanical folding/unfolding cycle even with a slow operation, whereas in a °exible polymer, the hysteresis almost disappears at a sufficiently slow operation. This suggests that the essential features of the structural transition of a semiflexible polymer should be interpreted at least on a two-dimensional phase space. The appearance of such large hysteresis is discussed in relation to different pathways in the loading and unloading processes. By using a minimal two-variable model, the hysteresis loop is described in terms of different pathways on the transition between two stable states.


Rod-coil copolymer We investigate the folding transition of a single diblock copolymer consisting of a semiflexible and a flexible blocks. We obtain the saturn shaped core-shell conformation in the folded state, where the flexible block form a core and the semiflexible block wrap around them. We find two distinctive features in the core-shell structures. (i) The kinetics of the folding transition in the copolymer are more efficient than that in a semiflexible homopolymer. (ii) The core-shell structure does not depend on pathways of the transition.

Two-state polymer Monte Carlo simulation of annealed copolymers of solvophobic/solvophilic monomers show collapsed globular states having a dynamic core-shell structures. In these, the core is mostly solvophobic while the core boundary contains an excess of solvophilic monomers. This two state model, where each monomer undergoes interconversion between solvophobic and solvophilic state, is a minimal version of models of neutral water soluble polymers such as PEO. The reduced surface tension of such core-shell structures suggests an explanation of the stability of PNIPAM globules as observed in the experiments of X.Wang, X.Qiu, C.Wu, Macromolecules, 1998, 31, 2972. The statitistics of the monomeric states along the chain vary with the degree of chain swelling. They are differ from those of quenched copolymers designed to create water soluble globules though both systems involve a core-shell structures.

AFMWith atomic force microscopy, full visualization of a single giant T4 DNAmolecules (166 kilo base pairs), the contour length of which is sufficient to examine the scaling property, was achieved. Fluorescence microscopic measurement was performed on exactly the same T4 DNA molecules. The results showed that there are three distinguishable regions in the scaling property R~Ln , where R, L, and n are the end-to-end distance, contour length and scaling exponent, respectively: ~i! n .1 when L,0.10 mm, ~ii! n.0.5 when 0.10 mm,L,4 mm, and ~iii! n.0.75 when L.4 mm. This conformational behavior is discussed in relation to self-avoiding walk in 2D.




2011Hiroyuki Kitahata, Natsuhiko Yoshinaga, Ken H. Nagai, and Yutaka Sumino
"Spontaneous motion of a droplet coupled with a chemical wave"
submitted movies are available here

2010Hong-Ren Jiang, Natsuhiko Yoshinaga, and Masaki Sano
"Active Motion of Janus Particle by Self-thermophoresis in Defocused Laser Beam"
Physical Review Letters, 105, 268302 (2010)
Editor's suggestion and Viewpoint in Physics, 3, 108 (2010) Debut of a hot “fantastic voyager”
movies are available here

Natsuhiko Yoshinaga, Jean-Francois Joanny, Jacques Prost and Pilippe Marcq
"Polarity patterns of stress fibers"
Physical Review Letters, 105, 238103 (2010)

2009 Takahiro Sakaue and Natsuhiko Yoshinaga
"Dynamics of Polymer Decompression: Expansion, Unfolding and Ejection"
Physical Review Letters, 102, 148302 (2009).

Hong-Ren Jiang, Hirofumi Wada, Natsuhiko Yoshinaga, and Masaki Sano
"Manipulation of Colloids by Nonequilibrium Depletion Force in Temperature Gradient"
Physical Review Letters, 102, 208301 (2009).

2008Natsuhiko Yoshinaga, E.I. Kats and A. Halperin
"On the Adsorption of Two-State Polymers"
Macromolecules, 41, 7744-7751 (2008)

Natsuhiko Yoshinaga
"Folding and unfolding transition in a single semiflexible polymer "
Physical Review E, 77, 061805 (2008).

2007Natsuhiko Yoshinaga
"Folding and unfolding transition in a single semiflexible polymer "

Natsuhiko Yoshinaga and Kenichi Yoshikawa
"Core-shell structures in single flexible-semiflexible block copolymers: Finding the free energy minimum for the folding transition"
in press (Journal of Chemical Physics)

N. Yoshinaga, D. J. Bicout, E.I. Kats and A. Halperin
"Dynamic Core Shell Structures in Two State Models of Neutral Water Soluble Polymersr"
Macromolecules, 40(6), 2201-2209 (2007)

2006N. Yoshinaga
"Transition kinetics of a single semiflexible polymer"
Progress of Theoretical Physics Supplement, 161, 397-402 (2006).

2005 N. Yoshinaga, K. Yoshikawa and T. Ohta
"Different pathways in mechanical unfolding/folding cycle of a single semiflexible polymer"
European Physical Journal E, 17, 485 (2005).

K. Yoshikawa and N. Yoshinaga
"Novel scenario on the folding transition of a single chain"
Journal of Physics: Condensed Matter, 17, S2817-S2823 (2005).

2002 N. Yoshinaga, K. Yoshikawa and S. Kidoaki
"Multiscaling in a Long Semiflexible Polymer Chain in Two Dimension"
Journal of Chemical Physics, 116, 9926 - 9929 (2002).

義永 那津人, 吉川 研一
日本ゴム協会誌, 75, 385-389 (2002)

2001N. Yoshinaga, T. Akitaya and K. Yoshikawa
“Intercalating Fluorescence Dye YOYO-1 Prevents the Folding Transitionin Giant Duplex DNA”
Biochemical and Biophysical Research Communications, 286, 264-267, (2001).

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