Lecture 1

Direct 3D observation of topological defect dynamics in liquid crystal
K. A. Takeuchi1,2,* and Y. Zushi11

Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
2JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan*kat@kaztake.org

Topological defects – topologically nontrivial structures that may exist in an orderparameter field – are generic concepts that abound in a wide variety of fields, ranging
from dislocations in crystal and disclinations in liquid crystal, to quantum vortices insuperfluid and cosmic strings in cosmology. One may therefore ask what features of
topological defects are common to different systems and what are unique to each. Liquid
crystal is a particularly interesting system to address such questions, partly thanks to its
amenability to direct optical observations, and also because of the recent surge of studies
on active nematics [1] showing the presence and important roles of topological defects in
microtubule bundles, bacterial colonies, and even in the body formation of a
microorganism.
Here we aim at direct observations and characterization of 3D structures and dynamics
of topological defects in nematic liquid crystal, namely disclination lines. Using confocal
microscopy and fluorescent dyes, we successfully observed relaxation dynamics of
disclination lines generated by a turbulent state [2]. In particular, we will report onreconnections of disclination lines, which are characteristic of such topological defectlines, and wish to argue what aspects of the results are common to different systems andwhat aspects are unique to liquid crystal. If time allows, we will also describe our interestsfrom the statistical physics viewpoint, which concerns universal scaling laws governinga certain class of non-equilibrium systems, observed in a collection of disclination lines
in a turbulent state [3].
[1] See, e.g., M.-A. Fardin and B. Ladoux, Nat. Phys. 17, 172 (2021) and references
therein.
[2] Y. Zushi and K. A. Takeuchi (in preparation).
[3] See, e.g., K. A. Takeuchi, Physica A 504, 77 (2018); Japanese readers may also referto K. A. Takeuchi, Ekisho 24, 218 (2020).

Lecture 2

Observation of liquid crystal soliton: topology and kinetics
Satoshi Aya*,1 and Fumito Araoka*,2
1South China Advanced Institute for Soft Matter Science and Technology (AISMST), School ofMolecular Science and Engineering (MoSE), South China University of Technology, Guangzhou
510640, China.
2RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
*

satoshiaya@scut.edu.cn (SA); fumito.araoka@riken.jp (FA)

Topological solitary waves, dubbed “solitons”, represent nontrivial and distorted
vector fields, which are distinct to the far-field background, exhibiting particle-like nature.
Generating and switching solitons [1]-[6], resembling topologically-protected states suchas magnetic skyrmions, have risen the tremendous interest in understanding solitonic
behaviors at the microscopic scale. Observing and manipulating them is vital tounderstand the fundamental nonlinear processes of the localization of waves. The utmost
challenge of this field is to understand the mechanism of the generation of the solitons
and the resultant possible topological structures and the control of their kinetics towards
active cargo transport and the like. Here, we present a novel example of generating aswarm of motile solitonic quasi-particles in micrometer-thick nematic liquid crystals [6].
The solitons are oscillating topological waves driven synchronized with the applied
electric field. We show that reversible generation-extinction processes of the solitons andthe subsequent motion control with variable angles can be achieved by simply tuning
frequency and amplitude of the electric field. How they perform the kinetic motion isbased on the electroconvection phenomena, primarily determined by the combinations of
the anisotropies of the effective wave flux and elastic deformation. These results offer aplayground for further development of soliton physics and applications like on-demandcargo transport.
[1] P. J. Ackerman and Ivan I. Smalyukh, Phys. Rev. Lett., 7, 011006 (2017).
[2] P. J. Ackerman and Ivan I. Smalyukh, Nat. Mater., 16, 426 (2017).
[3] A. Nych, J.-ichi Fukuda, U. Ognysta, S. Žumer, I. Muševic, Nat. Phys., 13, 1215
(2017).
[4] B.-X. Li et al. Nat. Commun. doi: 10.1038/s41467-018-05101-y (2018).
[5] Y. Shen and I. Dierking, Commun. Phys. doi: 10.1038/s42005-020-0288-4 (2020).
[6] S. Aya and F. Araoka, Nat. Commun. doi: 10.1038/s41467-020-16864-8 (2020).

Lecture 3

Ferroelectric-antiferroelectric phase transition with large
electromechanical response in a dipolar crystal
Kyohei Takae
Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo,
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
takae@iis.u-tokyo.ac.jp

Design and creation of functional materials are of great importance not only intechnological applications but also in condensed matter physics to obtain physicalprinciples how material function emerges. Soft materials such as polymer gels and liquid
crystals have complex internal structure. In these substances, internal degrees of freedom
with microscopic and mesoscopic length scale (e.g., liquid crystalline order) couples tomacroscopic deformation of the substances, which leads to soft elasticity and crosscoupling effects. This concept is also applicable to crystalline solids because the orderparameter characterizing phase transitions (e.g., dielectric polarization) couples withelastic strain [1]. However, simple physical principles to control soft mechanical response
via phase transitions involving spontaneous crystal rearrangement remain elusive.
Here we present a simple physical mechanism of such controllability using a simple
dipolar crystal model, which may capture an essence of phase transitions between
ferroelectric and antiferroelectric phases [2]. Each particle is ellipsoidal shape possessinga permanent dipole moment at its centre, and they form crystalline state at low
temperature spontaneously depending on dipolar ordering. By performing moleculardynamics simulation using this off-lattice model, we reveal that energetic frustration
between the dipole-dipole interaction and interparticle steric interaction is a key to control
ferroelectric-antiferroelectric phase transition accompanied with structuraltransformation. This phase competition with large lattice misfit is responsible for large
electromechanical response under external electric field and mechanical stress.
We also present another mechanism to control dielectric and electromechanical properties
with the addition of impurities, which disturb formation of macroscopic polar domain [3].
Finely divided polar domains surrounded by the impurities easily respond to external
electric fields and mechanical stress with characteristic dielectric dispersion. The
similarity between our system and the relaxor ferroelectrics is discussed.
[1] A. Onuki, Phase Transition Dynamics (Cambridge University Press, 2002).
[2] K. Takae and H. Tanaka, Proc. Natl. Acad. Sci. 115, 9917 (2018).
[3] K. Takae and A. Onuki, J. Phys.:Condens. Matter 29, 165401 (2017).

Lecture 4

Dynamic Assembly of Colloidal Nanosheets
Koki Sano
RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
JST PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
koki.sano [at] riken.jp

In living organisms, anisotropic colloids, such as proteins, self-assemble into wellorganized hierarchical structures to realize spatiotemporally controlled advanced
functions[1]. It is a major challenge in the field of materials science to mimic such
sophisticated systems by using artificial building blocks. For this purpose, we havefocused on titanate nanosheets (TiNSs)[2] as a promising building block. TiNS is a
unilamellar nanosheet dispersed in water, featuring ultra-thin (0.75 nm) and extra-wide(several micrometers) dimensions. Owing to its dense negative charges on its surface, thestrong electrostatic repulsion works between TiNSs in addition to the van der Waals
attraction. These competitive repulsive and attractive forces allow for interlocking TiNSs
in a cofacial manner at a fixed relative position, as described in the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory.
Recently, we have established a rational strategy to precisely control the electrostatic
repulsion between TiNSs, so that we can freely tune the distance between TiNSs[3]. As aresult, we succeeded in constructing dynamic assemblies of TiNSs, leading to life-likesoft materials, such as "a dynamic photonic crystal like tropical fish[3]", "an anisotropichydrogel like articular cartilage[4]", "a mechanically adaptive hydrogel like sea
cucumbers[5]", and "a propagating wave like ciliary waves[6]". In the presentation, a seriesof these studies will be discussed.

[1] K. Sano et al. Angew. Chem. Int. Ed. 57, 2532–2543 (2018).
[2] T. Sasaki et al. J. Am. Chem. Soc. 118, 8329–8335 (1996).
[3] K. Sano et al. Nat. Commun. 7, 12559 (2016).
[4] K. Sano et al. Angew. Chem. Int. Ed. 57, 12508–12513 (2018).
[5] K. Sano et al. Nat. Commun. 11, 6026 (2020).
[6] K. Sano et al. Submitted.

Lecture 5

Self-organization of deformable colloidal particles at liquid interfaces
Daisuke Suzuki
Graduate School of Textile Science & Technology,
and Research Initiative for Supra-Materials, Interdisciplinary Cluster for Cutting Edge Research,Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan*d_suzuki@shinshu-u.ac.jp

Interfacial behaviors of soft hydrogel microspheres (microgels), which are colloidal
particles of cross-linked polymeric networks, will be presented. The author focuses on
the drying behavior of aqueous dispersions containing poly(N-isopropyl acrylamide)(pNIPAm)-based microgels. Different from dispersions containing solid microspheres
such as polystyrene and silica ones, we found that soft and deformable microgels did notexhibit “coffee-ring effect”, which results in ring-like stain after dispersions evaporate.
Our group has investigated that the self-organization of microgel dispersions during
evaporation exhibit unique drying behaviors due to their selective adsorption at theair/water interface of sessile droplets. In the presentation, effects of size, crosslinking
densities, types of chemical species, charge, shape for microgels, substrates and so forthon the phenomenon will be summarized. Our findings of this study would promote further
development in many applications that understanding the interfacial behaviors of soft anddeformable microgels is crucial, including emulsions, foams, coating and sensors.
Partially reprinted with permission
from references [1] [2], and [5]Copyright (2012), (2018), and(2019) American Chemical Society,respectively,references[3]
Copyright (2018) Royal Society ofChemistry, and references [4]Copyright (2019) Wiley-VCH.

[1] Horigome, K. et al. Langmuir 28, 12962 (2012).
[2] Takizawa, M. et al. Langmuir 34, 4515 (2018).
[3] Minato, H. et al. Chem. Commun. 54, 932 (2018).
[4] Kenshiro, H. et al. Angew. Chem. Int. Ed. 58, 7294 (2019).
[5] Minato, H. et al. Langmuir 35, 10412 (2019).

Lecture 6Nonequilibrium nature in meniscus splittingof aqueous polysaccharide suspensions
K. Okeyoshi*, K. Budpud. G. Joshi, and T. Kaneko
Graduate School of Advanced Science and Technology, Japan Advanced Institute of Science andTechnology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
*

okeyoshi@jaist.ac.jp

The air-water interface is expected to play an important role in establishing a universal
model of dissipative structures in nature. Viscous fingering, as an example of fluidic flow,
is an unstable situation that is widely known as tears of wine. This has been explained
through the Marangoni effect, coffee ring effect, Saffman-Taylor instability, etc. However,
due to the transitional nature of these phenomena, there are few strategies forimmobilizing such fluidically regulated interfaces. Recently, such phenomena have been
applied successfully to an immobilized structure by controlling the evaporation of a
mixture of biopolymer and water.1-7
In this study, we present a brief discussion of nonequilibrium phenomenon, “meniscussplitting”. More precisely, an air-liquid interface is divided into multiple interfaces topartition a space. In particular, by using a mixture of polysaccharides and water, amacroscopic pattern following a specific rule could be confirmed. When the mixture isdried from a top open cell, the polymer forms deposits at specific positions to split themeniscus by bridging a millimeter-scale gap. Because water irreversibly evaporates fromthe liquid phase to the air phase through a gap, the air-liquid interface is in a
nonequilibrium state between polymer deposition and water evaporation. The interfacial
instability is comparable to the mechanical instability of gels at the phase transition or tothe skin layer of gel surfaces during shrinking. Furthermore, the deposited polymer film
acts as vapor-sensitive materials. Here, the phenomenon and the material’s behavior
would be discussed from physicochemical viewpoints.
[1] Okeyoshi, et al, Scientific Reports 11, 767 (2021).
[2] Okeyoshi, et al, Polymer Journal 52, 1185 (2020).
[3] Budpud, et al, Small 16, 2001993 (2020).
[4] Joshi, et al, Journal Colloid and Interface Science 546, 184 (2019).
[5] Okeyoshi, et al, Advanced Materials Interfaces 5, 1701219 (2018).
[6] Okeyoshi, et al, Scientific Reports 7, 5615 (2017).
[7] Okeyoshi, et al, Biomacromolecules 17, 2096 (2016).

Emergent functions in a swarm of biomolecular motors
Akira Kakugo
1Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Japan,
2

Faculty of Science, Hokkaido University, Sapporo, Japan,

Recent advancements in molecular robotics have been greatly contributed by the progress invarious fields of science and technology, particularly in supramolecular chemistry, bio- andnanotechnology, and informatics. Yet one of the biggest challenges in molecular robotics has
been controlling a large number of robots at a time and employing the robots for any specifictask as flocks in order to harness emergent functions. Swarming of molecular robots has
emerged as a new paradigm with potentials to overcome this hurdle in molecular robotics.
In this this talk, I will discuss the latest developments in swarm molecular robotics,
particularly emphasizing the effective utilizationof bio- and nanotechnology in swarming ofmolecular robots. Importance of tuning themutual interaction among the molecular robots
in regulation of their swarming is introduced.
Successful utilization of DNA, photoresponsive
molecules, and natural molecular machines inswarming of molecular robots to provide themwith processing, sensing, and actuating ability ishighlighted. The potentials of molecular swarm
robots for practical applications by means of
their ability to participate in logical operations
and molecular computations are also discussed.
Prospects of the molecular swarm robots inutilizing the emergent functions throughswarming are also emphasized together with
their future perspectives.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]

E. Bonabeau, M. Dorigo, and G. Theraulaz, Oxford: Oxford University Press; 1999.
M. Rubenstein, A. Cornejo, and R. Nagpal, Science. 345, 795 (2014).
N. C. Seeman, Trends Biotechnol. 17, 437 (1999).
D. Inoue and A. Kakugo Nature communications, 7:12557; (2016)
J. J. Keya and A. Kakugo et al. Nature communications, 9, 453 (2018)
K. Matsuda and A. Kakugo et al. Nano Letters, 19, 6, 3933 (2019)
D. Inoue and A. Kakugo et. al. ACS Nano, doi.org/10.1021/acsnano.9b01450 (2019)