日時：2024年4月19日（金）14:00-
場所：理学部5号館401号室
講師：Žiga Kos (University of Ljubljana, Slovenia)
題目：Dynamics of colloids and disclinations in driven and active nematic fluids
要旨：Fluids with nematic orientational order emerge in various materials,
from nematic liquid crystals to biological and synthesised active
matter. I will show how the nematic order can break the symmetry and
lead to propulsion of externally pulsated and rotated colloidal
inclusions, which can even perform essential robotic tasks. Notably,
orientational order emerges also in active materials, where in three-
dimensional active nematics defects appear as dynamic disclination lines
and loops. I will present dynamic modes of individual loops and
reconfiguration of loops in the dynamic steady-state of active
turbulence.The dynamic steady-state defect density depends on activity
and other viscous and elastic material parameters. I will show how
intrinsic chirality increases the defect density and can potentially
even lead to a transition into an active blue phase. This work aims to
provide insight into 3D non-equilibrium active and driven nematic
systems from the perspective of the topology and dynamics of the
emergent 3D defects.
2023
日時：2023年9月15日（金）14:00-
場所：理学部5号館401号室
講師：Nina Lorenz, Christopher Wittenberg, Thomas Palberg
(Institute of Physics, Johannes Gutenberg Universität Mainz, Germany)
題目：Porous crystals from aggregate containing charged sphere suspensions
要旨：Porous crystals are valued in many applications for their unusual elastic and transport
behaviour. Despite occasional observations, porous colloidal crystals thus far evaded
reproducible fabrication. We here study possibilities for their formation from multicomponent
colloidal melts. Simple mixtures show a rich microstructure, but no pore formation. Systems
containing small aggregates show an enhanced nucleation behaviour. However, charged colloidal
spheres in low-salt suspensions containing moderately sized aggregates comprising some 5-10
particles reveal the formation and stabilization of a porous crystalline microstructure.
Using optical microscopy, we observe the transformation of an initially crystalline colloidal
solid with homogeneously incorporated aggregates to individual, compositionally refined
crystallites of perforated morphology coexisting with an aggregate-enriched fluid phase
filling the holes and separating individual crystallites. We show that this route to porous
materials is neither restricted to nominally single component systems nor to a particular
microstructure to start from. However, it necessitates an early rapid solidification stage
during which the aggregates become trapped in the bulk of the host-crystals. A preliminary
kinetic characterization shows their growth to follow power law behaviour. The thermodynamic
stability of the reconstructed crystalline scaffold against melting under increased salinity
was found comparable to that of pure phase crystallites grown very slowly from a melt.
Future implications of this novel route to porous colloidal crystals are discussed.
日時：2023年9月12日（火）14:00-
場所：理学部5号館401号室
講師：Seyed Reza Seyednejad (Faculty of Mathematics and Physics, University of Ljubljana,Slovenia)
題目：Elastic effects in the nematic liquid crystals:
From colloidal self-assembly to microfluidics due to the anchoring-change
要旨：In this talk, I will review some of my recent works on colloidal self-assembly,
conically degenerate surface anchoring, and flow flux driven by active anchoring in
nematic liquid crystals (NLCs). I will begin with the energy potentials we have proposed
in Q-tensor terms, to ensure the conically degenerate surface anchoring in the numeric studies.
Such surface anchoring gives the freedom to the nematic director to align itself on
a cone with a fixed easy angle to the surface normal. We used that potential to describe
the hexadecapolar nature of the interactions between spherical colloids with conic surface
anchorings. Then I will discuss the topological effects that such boundary condition
imposes on the spherical shells and how the equilibrium configuration changes with
respect to the planar shells. I will also talk about the self-assembly of hollow
pyramidal cones and the unexpected dipolar behavior we observed under some circumstances.
Then I will discuss some of the research I am currently doing, ranging from the NLC flow
flux driven by a time-changing surface anchorings, to the colloids topological effects
in the biaxial NLCs.
日時：2023年6月13日（火）16:00-
場所：理学部5号館401号室
講師：Yasutaka Iwashita (Kyoto Sangyo University)
題目：Creating bulk ultrastable glasses by random particle bonding
要旨：Glasses are usually produced by slowly cooling a melt, with slower
cooling leading to samples of higher stability. Accessing highly
stable glasses is important not only to answer fundamental questions,
but also for technological applications. A recent breakthrough in this
direction is the synthesis of ultrastable glasses via physical vapor
deposition techniques [1]. However, this technique can produce only
thin film samples. Here, we propose a novel approach to generate
ultrastable glassy configurations in the bulk, via random particle
bonding, and using computer simulations we show that this method does
indeed allow for the production of ultrastable glasses [2].
The seminar starts from the brief review of ultrastable glasses,
and then our approach is presented.
1. S. F. Swallen et al. Organic glasses with exceptional
thermodynamic and kinetic stability. Science 315, 353 (2007).
2. M. Ozawa, Y. Iwashita, W. Kob and F. Zamponi,
“Creating bulk ultrastable glasses by random particle bonding”,
Nature Communications, 14, 113 (2023).
2022
日時：2023年2月21日（火）16:00-
場所：理学部5号館401号室
講師：Armand Barbot （京都大学大学院 情報学研究科）
題目：Study of plasticity in amorphous and crystalline materials
using atomic scale simulations
要旨：
This seminar will focus on two main topics: (a) the study of plasticity and shear bands in metallic glasses, and (b) the multi-scale modeling of plasticity in crystalline materials using machine learning algorithms.
(a) In a first part, we will focus on the study of plasticity in metallic glasses. The understanding of plasticity in metallic glasses is nowadays a very active research field. Produced for the first time in the sixties, metallic glasses are promising materials thanks to their very high yield strength. However, they also have the defect of being brittle. This high brittleness is explained by the formation of shear bands in which plasticity concentrates in the first stage of the deformation.
Using atomic simulations and a new method developed to measure the local hardness of these simulated materials, we will study the importance of rejuvenation in the formation of shear bands and in particular the influence of the preparation and size of the system. We will also look at the evolution of the shear band width with the applied stress and compare it with an analytical model.
(b) In the second part, we will focus on the nucleation of thermally activated heterogeneous dislocations. The nucleation of thermally activated heterogeneous dislocations is the dominant mechanism of plasticity for crystals smaller than 100-200nm such as metallic or semiconductor nano-pillars or nano-films. Nucleation is thus an essential phenomenon for the understanding and control of mechanical properties at the nanoscale, and thus, for example, to allow the miniaturization of electronic components subjected to high stress and temperature. This mechanism also plays an important role in the understanding and modeling of crack propagation, as nucleations blunt the crack tips, thus slowing down their propagation speed.
Although this phenomenon can be reproduced in numerical simulations at the atomic scale, its implementation in Discrete Dislocation Dynamics (DDD) simulations, allowing to simulate materials on larger size and time scales, is still missing. We propose here approaches based on the use of machine learning algorithms to allow the implementation of these nucleations in DDD simulations based on results obtained with atomic scale simulations.
日時：2023年1月5日（木）16:00-
場所：理学部5号館401号室
講師：John Russo (Sapienza Università di Roma, Italy)
題目：Water is a (half) empty liquid
要旨：It is becoming increasingly clear that water’s structure has enough empty space to
accommodate a second liquid at high pressure.
Exploiting this analogy, we classify water together with a larger group of liquids, aptly named
Empty Liquids, whose constituents arrange in a random network through reversible bonds [1].
These bonds can be physically realized with a variety of interactions, such as hydrogen bonding,
lock-and-key interactions, DNA base pairing, hydrophobic, dipolar, and even entropic
interactions. Materials that fall in the category of empty liquids go from patterned colloidal
particles, clays, DNA wireframe origamis, all the way down to atoms, like silicon.
In this seminar we make the case that water is a Half-Empty liquid, which, on top of the typical
empty liquid’s behaviour, can display complex properties such as thermodynamic and dynamic
anomalies, the possibility of liquid–liquid phase transitions, and the crystallization of open
crystalline structures. Finally, we will try to answer the age-old question whether amorphous
glasses are half-empty too [2].
[1] J. Russo, F. Leoni, F. Martelli, F. Sciortino, Rep. Prog. Phys. 85, 016601 (2022)
[2] F. Martelli, F. Leoni, F. Sciortino, J. Russo, J. Chem. Phys. 153, 104503 (2020)
日時：2022年12月20日（火）13:00-
場所：理学部5号館401号室
講師：Dr. Yukio Kajihara (Hiroshima Univ.)
題目：Understanding the specific heat of liquids by focusing on critical fluctuations
要旨：How to understand specific heat of liquids ?
The equipartition theorem is the main principle regarding the specific heat of materials. The isochoric specific heats Cv are, 1.5R (R: gas constant) for monoatomic gases, 2.5R for diatomic molecular gases, and 3R for elemental solids (Dulong-Petit law): The concept of "degree of freedom" can universally interpret the specific heat of gases and solids irrespective of materials. What about liquids, then ? Liquids have higher specific heats than gases and solids, which is explained by the concept that they can have various "configurations" and thus have an extra degree of freedom compared to solids and gases. However, to be honest, it is unclear what kind of "configuration" contributes to specific heat and to what extent.
Meanwhile, when we look at the wide range of temperature-pressure dependence of Cv of liquid (fluid) water [1], we notice a simple fact: Two distinct rises are seen and they characterize the overall feature of Cv of water. The one in the high temperature region is topped by the critical point of the liquid-gas phase transition (LGT), and is clearly due to the critical fluctuation of LGT. The fact that critical fluctuation increase the specific heat is a fundamental concept described in textbooks. The other one in the low-temperature region extends to the top of the low-pressure supercooled region, and it is reasonable to recognize that it is due to the critical fluctuation associated with the liquid-liquid phase transition (LLT), which is proposed to have a critical point in the supercooled region. In other words, it is possible to construct a framework for interpreting the specific heat of liquids by considering the critical fluctuations associated with these two phase transitions as the entity of "configuration".
In the talk, I will introduce the detail of this framework while showing our experimental results on "dynamical fluctuations" of water [2]. Critical fluctuation of LLT differs from that of LGT in several respects, and it is important to discuss them in an organized manner. The final goal of the framework proposed here is to develop a unified concept of disordered materials, including glass transition liquids. I would be happy to share this final goal with you !
[1] W. Wagner and A. Pruss, J. Phys. Chem. Ref. Data 31, 387 (2002)
[2] Y. Kajihara et al., arXiv 2111.06589
日時：2022年10月6日（木）13:30-
場所：理学部5号館413号室
講師：Anupam Sengupta (the University Luxembough)
題目： Microbial Active Matter
要旨：Understanding how microbes interface, exchange and communicate
with their local surroundings is central to the grand quest for a theory
of microbial ecology. From simple to complex fluids, from compliant to
rigid environments, microbes inhabit plethora of dynamic settings
spanning vastly different structures, internal energies, and interacting
cues. Currently we lack a biophysical framework that could explain,
generalize, and crucially, predict the if-s, the how-s, and the why-s
of the microbe-environment feedbacks. Research in our lab aims to fill
this gap by interfacing soft and active matter physics with microbiology
and genetic engineering, often with generous support of 3D
microfabrication, automation, quantitative imaging and machine learning
tools. Using vignettes from our recent works in bacterial and
phytoplankton systems [1-4],we will see microbes – under ecologically
relevant settings – in an active matter framework, and discuss their
individual and collective traits (behavior and physiology) in the
context of microbial adaptation to changing environments. I will
highlight the generality of our results across populations and taxa,
touching upon concepts of emergent intelligence associated with the
active microbial matter at collective scales. I will conclude by
showcasing some of our recent efforts to leverage the microbes-
mechanics-materials nexus in understanding functions of microbes
associated with specific cancer types, and more broadly, to harness the
biophysical feedbacks for the next generation of bioremediation and
diagnostic tools.
[1] Sengupta, Carrara, & Stocker, Nature 543, 555-558, 2017
[2] Sengupta, Dhar, Danza, Ghoshal, Müller, Kakavand, Science Advances (in press)
[3] You, Pearce, Sengupta, Giomi, Physical Review X 8, 031065, 2018
[4] Sengupta, Frontiers in Physics 8, 2020
[5] Dhar, Thai, Ghoshal, Giomi, & Sengupta, Nature Physics 18, 945-951, 2022
これまでのセミナー
日時：2019年5月27日（月）10:30-
場所：理学部5号館413号室
講師：Armand Barbot (Ecole Normale Superieure, France)
題目： Characterization of shear bands and plasticity in model glasses at the atomic scale
日時：2018年6月12日（火）13:30-
場所：理学部5号館401号室
講師：藤谷洋平氏 （慶応大学)
題目： Drag coefficient of a circular liquid domain in a flat fluid
membrane a bit close to the demixing critical point
日時：2017年9月8日（金）14:00-
場所：理学部5号館401号室
講師：Ram Adar (School of Physics and Astronomy, Tel Aviv University, Israel)
題目： Bjerrum pairs in ionic solutions: a Poisson-Boltzmann approach
日時：2017年4月26日（水）16:00-
場所：基礎物理学研究所 研究棟・講義室 K206 (場所に注意)
講師：Subhadeep Roy (Earthquake Research Institute, University of Tokyo)
題目： Fracture in Different Scales: A Statistical Mechanical Approach
日時：2017年2月21日（火）13:30-
場所：理学部5号館401号室
講師： 高江 恭平氏 (東京大学)
題目：Ferroelectric glass of spheroidal dipoles with impurities
日時：2016年12月7日（水）15:00-
場所：基礎物理学研究所 研究棟・講義室 K206 (場所に注意)
講師：Anael Lemaitre (NAVIER, URM 8205, Ecole des Ponts, IFSTTAR, CNRS, UPE, France)
題目：Anomalous phonon scattering and elastic correlations in amorphous solids
日時：2016年11月28日（月）13:30-
場所：理学部5号館413号室
講師：Lee, Kuang-Wu (Friedrich-Alexander-University, Erlangen, Germany)
題目：Mesoscopic Simulation of Nematic Liquid Crystals in Microfluidics
日時：2016年3月15日（火）13:00-
場所：理学部5号館401号室
講師：Tatsuya Ishiyama (石山 達也氏) (Graduate School of Science and Engineering, University of Toyama )
題目：Molecular Dynamics Study of Structure and Spectroscopy at Liquid Interface
日時：2015年12月8日（火）13:00-
場所：理学部5号館401号室
講師：Itsuo Hanasaki (花崎 逸雄氏) (Tokyo University of Agriculture and Technology)
題目：Applied statisitical mechanics for engineering: from molecular dynamics and coarse-graining
to big data analysis of fluctuation measurements and single-particle characterization
日時：2015年11月17日（火）13:00-
場所：理学部5号館401号室
講師：Tsuyoshi Yamaguchi (山口 毅氏) (Nagoya University)
題目：Theory on dynamics of electrolyte solutions: Interplay between dynamics of bound pairs and ionic atmosphere
日時：2015年11月13日（金）17:00-
場所：理学部5号館401号室
講師：Kyohei Takae (高江 恭平氏) (University of Tokyo)
題目：Water in a Capacitor: Structure, Fluctuation, and Response
日時：2015年6月16日（火）13:00-
場所：理学部5号館401号室
講師：Takuya Sugimoto (Graduate School of Life and Environmental Sciences, University of Tsukuba)
題目：Aggregation Rates of Charged Colloidal Particles in a Couette Flow: Trajectory Analysis with Non-linear Poisson-Boltzmann Solution
日時：2015年6月2日（火）13:30
場所：理学部5号館401号室
講師：Hayato Shiba （芝 隼人）(The University of Tokyo)
題目：Membrane simulation - elasticity, surface tension, and some applications
日時：2015年1月20日（火）15:00
場所：理学部5号館401号室
講師：Toshiki Mima （美馬 俊喜氏）(The University of Tokyo)
題目：Molecular dynamics simulation of fluids in nanopores
日時：2014年11月18日（火）10:30
場所：理学部5号館413号室
講師：Jack F. Douglas (National Institute of Standards and Technology)
題目：Cooperative Motion and Structural Relaxation in Glass-Forming Materials
日時：2014年11月11日（火）13:00
場所：理学部5号館401号室
講師：Hiroaki Yoshida (Toyota Central R&D Labs.)
題目：Analysis of electrokinetic transports of nano-confined electrolyte solutions by means of the molecular dynamics simulations
日時：2014年8月27日（水）13:30
場所：理学部5号館413号室
講師：Anael Lemaitre (Laboratoire Navier (UMR 8205), Universite Paris-Est, France)
題目：Structural relaxation is a scale-free process
日時：2014年5月14日（水）15:30
場所：理学部5号館413号室
講師：Mohammad Reza Mozaffari (University of Qom, Qom, Iran )
題目：Pair interaction between colloidal particles in nematic liquid crystal
日時：2013年11月15日（月）16:00
場所：理学部5号館401号室
講師：AMiha Ravnik (Faculty of Mathematics and Physics, University of Ljubliana, Centre of Excellence NAMASTE, Slovenia)
題目：Topological superstructure in nematic liquid crystal colloids
日時：2013年4月22日（月）13:30
場所：理学部5号館413号室
講師：Dr. Flavio Romano (Department of Chemistry, University of Oxford, UK JSPS Fellowship, University of Tokyo)
題目：OxDNA: a coarse-grained model for simulations of DNA
場所：理学部5号館413号室
講師：Jure Dobnikar (Department of Chemistry, University of Cambridge and Jozef Stefan Institute, Ljubljana, Slovenia)
題目：Field-induced self-assembly of suspended colloidal membranes
日時：2012年11月14日（水）16:00
場所：理学部5号館413号室
講師：Paddy Royall ((Bristrol University, UK)
題目：Colloidal and metallic liquids out of equilibrium : linking structure and kinetics
日時：2012年9月11日（火）14:30
場所：理学部5号館401号室
講師：Francesca Serra （イタリア ミラノ大学 9/7-12/6まで相転移に滞在）
題目：Memory from topology: an experimental point of view
日時：2012年7月12日（木）10:30
場所：理学部5号館413号室
講師：波多野 恭弘氏 (東京大学 地震研究所)
題目：Granular friction in a wide range of shear rates
日時：7月11日（水）15:30
場所：理学部5号館413号室
講師：Nasser Mohieddin Abukhdeir (Japan Society for the Promotion of Science Visiting Fellow* National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba, Ibaraki Prefecture, Japan)
題目：Formation and Dynamics of Smectic-A Liquid Crystals
日時：2012年7月10日（火）13:30
場所：理学部5号館401号室
講師：貞包 浩一朗氏 (KEK)
題目：The shear effects on a mixture of water / organic solvent / antagonistic salt
日時：2012年4月23日（月）16:00
場所：理学部5号館401号室
講師：Daniel Beysens (CEA and ESPCI, Paris, France)
題目：Adsorption on colloids and flocculation
日時：2010年9月3日(金）午後３時-
場所：理学部５号館４０１号室
講師： Didier R. Long (Laboratoire Polymeres et Materiaux Avances: CNRS/Rhodia; Rhodia Reserches et Technologies, France)
題目： Slow domains percolation in polymer melts and blends close to the glass transition: a unifying concept regarding bulk dynamics, dynamics in the vicinity of interfaces, and the physical properties of nanocomposites
日時：2009年1月21日(木）15時30分-
場所：理学部５号館４１３号室
講師：Prof. Turab Lookman (Theoretical Division, Los Alamos National Laboratory, Los Alamos, USA)
題目：Microstructure and glassy phenomena for ferroelastic transitions in two and three dimensions using strain pseudo-spin models
