A01 Public Participation Research (2007-2008)

Urayama group

Slow Dynamics of Polymer Gels under External Stress Fields

 

[ Leader ]
Kenji Urayama Kyoto University

research subject

Polymer gels containing much amount of solvent behave as soft solids without flowing. Equilibrium swelling of gels is considerably sensitive to external forces. The gels may swell further or shrink in response to external forces. The static and dynamic properties of these phenomena reflect the elastic constants such as osmotic Poisson's ratio and the friction coefficient between solvents and networks. Most of the earlier studies investigated the behavior in the small strain region holding the linear elasticity theory. The present study focuses on the large deformation behavior, and experimentally studies the strain-rate effects on fracture phenomena, Poisson's ratio and stress. According to our preliminary experiment, when the strain-rate is lowered down to the time-scale comparable to the diffusion of polymer networks, we observe a marked strain-rate effect on the stress and fracture mode. Our results will provide an important basis for the design of soft actuator based on polymer gels.

Sakurai group

Physics in Ordering of Spherical Microdomains Dispersed in Entangled Matrix

 

[ Leader ]
Shinichi Sakurai Kyoto Institute of Technology

research subject

Block copolymers form spherical microdomains in case of compositions around 0 or 1 (far away from 0.5). Furthermore, such spherical microdomains order in a body-centered cubic lattice (bcc). However, a face-centered cubic lattice (fcc) will be available when homopolymers are blended. In this case, the added homoplymers are intended to act as spacers fullfilling up open space in the Wigner-Seitz cell for the fcc packing of spheres, which can stabilize the fcc packing without causing frustrations (conformational entropy losses due to chain stretching or contraction) of corona chains anchored to a surface of spheres. In case when the fcc packing will be attained by adding homopolymers, we will study on influences of entanglements on the ordering process of spheres into the fcc lattice. For this purpose, molecular weights of the homopolymers will be varied to cover the concentration range from non-entangled to highly-entangled states. The lattice disordering temperature of fcc and the rate of the lattice disordering will be evaluated by conducting temperature-dependent small-angle X-ray scattering measurements.

Yokoyama group

Non-Equilibrium Structures through Swelling Processes of Non-Homogeneous Systems

 

[ Leader ]
Hideaki Yokoyama The University of Tokyo

research subject

When block copolymer thin films are immersed in a selective solvent, the thin films change the surface composition and absorb the selective solvent in the solvent-philic domains. Such surface segregation and absorption of solvent causes structure reconstruction. We investigate the pathway of such structure reconstruction and porous structures after removing the selective solvent.

Sato group

Association and Rheological Behavior of Polymers and Supra-Molecular Polymers in Solution

 

[ Leader ]	[ Member ]
Takahiro Sato Osaka University	Toshiyuki Shikata Osaka University

research subject

Associating polymers and surfactant molecules, which are utilized in various industrial fields as rheology control agents, colloid-stabilizers, drug derivery systems, and so on, form micelles or supramolecular polymers in solution. Our research group aims at establishing not only the characterization method of the micelles and supramolecular polymers but also the relationship between their association characteristics and various properties. The following systems are our present research objects: (1) threadlike micelles formed by low-molar mass surfactants in aqueous media; (2) threadlike aggregates of low-molar mass gelling agents formed with hydrogen bonding in organic solvents; (3) micelles of amphiphilic polyelectrolytes in aqueous solutions; (4) complexes formed by polyacids and polyamines; (5) aggregates of thermally denatured proteins and polysaccharides as well as protein polysaccharide complexes; (6) reverse micelles of living bifunctional polymer anions in non-polar solvents.

Takahashi group

Structure and Dynamics of Physically Cross-Linked Interpenetrated Networks

 

[ Leader ]
Yoshiaki Takahashi Kyusyu University

research subject

To obtain fundamental knowledge of the structure control methods of interpenetrating networks with physical cross-linking, the network structure and rheological properties of poly (vinyl alcohol)/sodium polyalginate (PVA/ALG) aqueous solutions with low ALG contents (ALG<20wt%) are examined by means of rheological measurements. It is known that the PVA and ALG are cross-linked by micro-crystalline and egg-box junction, respectively, which can be independently controlled when entanglement density is not so high. The effects of gelation sequence, temperature history, shear flow, and etc. will be examined. At the same time, new physically cross-linked IPNs will be searched mainly for biopolymers, which have abilities of hydrogen bonding and crystallization to study the formation of IPNs under various conditions.

Saito group

Structure and Properties of Im3m Phase in Thermotropics

 

[ Leader ]
Kazuya Saito University of Tsukuba

research subject

A tricontinuous mesophase (space group Im3m), which has not been found in polymers and lyotropic liquid crystals, is known in addition to a standard Gyroid phase (space group Ia3d) for neat thermotropic liquid crystals having low-molecular-mass. This project aims at the clarification of static and dynamical characteristics of the Im3m phase while paying attention on the countability of small molecules (in comparison with polymers). Molecular aggregation mode will be determined for the Im3m and Gyroid phases and compared with polymers and lyotropic liquid crystals. Precise adiabatic and modulation calorimetry will reveal the anomaly in the equilibrium entropy fluctuation at and the kinetics upon the phase transition between the Gyroid and Im3m phase.

Tanaka group

Nano-Healing Based on Interfacial Chain Dynamics

 

[ Leader ]	[ Member ]
Keiji Tanaka Kyushu University	Toshihiko Nagamura Kyushu University

research subject

In general, dynamics at the surface of polymers is faster than that in the corresponding bulk state. Thus, if a temperature is adequately chosen, molecular motion with a relatively large scale can be released only at the surface. When two polymer films were attached and then annealed even at a temperature above the surface and the below the bulk glass transition temperatures, the interface between the films evolved on nanometer level with increasing time, resulting in the adhesion for the films. In this study, the adhered area is also scaled down to nanometer as well as the interfacial thickness, so-called "nano-healing". We first establish how the adhesion strength can be precisely examined. Also, hierarchical molecular motion in the adhered interfacial region is simultaneously studied. Combining nano-healing results with non-equilibrium dynamics of surface chains/segments, we finally rationalize the molecular mechanism of nano-healing.

A02 Public Participation Research (2007-2008)

Hamada group

Raft Domain Formation in Model Membranes Induced by Lateral Pressure

 

[ Leader ]
Tsutomu Hamada Japan Advanced Institute of Science and Technology

research subject

During the last decade, microdomains such as lipid rafts, within cell membranes, have attracted considerable attention as platforms that sort proteins and form endocytic carriers. Cell-sized multicomponent liposomes, raft-exhibiting model membranes, are efficient tools for studying physico-chemical properties of the microdomains. Here, we investigate the structural change in domain patterns and membrane morphology induced by lateral pressure, using an optical microscope equipped with a focused laser and micromanipulation system. Then, we develop a cell-like membrane, i.e., a liposome with asymmetric leaflets similar to an actual cytomembrane. This will aid in clarifying the mechanism for stabilizing raft domains in terms of the lateral pressure balance.

Yamazaki group

Topological Changes of Biomembranes Induced by their Interaction with Substances and by External Field

 

[ Leader ]
Masahito Yamazaki Shizuoka University

research subject

Biomembranes / lipid membranes are one of important soft matters in biological systems. Their topological conversions and structural changes occur due to electrostatic interactions or mechanical stresses under nonequilibrium conditions, which are induced by interactions of the membranes with various external substances or external fields. In this project, we investigate irreversible topological changes of lipid membranes induced by external substances or external fields to elucidate their kinetic pathways and mechanisms. Especially we focus our investigation on two physiologically important topological changes of biomembranes / lipid membranes as follows. (1) We investigate elementary processes and physical factors of the pore formation in lipid membranes induced by interactions of antimicrobial peptides with the membranes and elucidate the mechanism of their pore formation. (2) Phase transitions between bicontinuous cubic phases and multilamellar vesicles of lipid membranes in the Lα phase and also the structural transformations from large unilamellar vesicles (LUVs) to cubic phases are induced by interactions of peptides or ions with the membranes. We investigate detailed conditions and elementary processes of these phase transitions and structural transformations and elucidate their mechanisms.

Kurihara group

Structures and Stability of Binary Liquids Confined between Solid Surfaces

 

[ Leader ]	[ Member ]
Kazue Kurihara Tohoku University	Masashi Mizukami Tohoku University

research subject

When liquid molecules are confined in a nano-space, the properties of liquids become quite different from those of the bulk (e.g. highly ordered structure of liquid molecules, drastic increase of the viscosity). The developments of characterization techniques on nano-meter scale such as the surface forces measurement allow us to investigate these phenomena at a molecular level. Our aim is to understand and control these remarkable structure and dynamics of binary liquid induced by applying the external fields such as the confinement and shear. The static and dynamic structures of binary liquid in a restricted space are investigated using the resonance shear measurement and FECO (fringes of equal chromatic order) spectroscopy which we developed based on the surface forces apparatus (SFA). To understand the factors (e.g. molecular structure, composition, compatibility, and affinity with the surface) to determine these properties, we also study the phenomena by molecular simulations.

Yamasaki group

Conformational Analyses of Single Polyelectrolyte Molecules

 

[ Leader ]
Yuichi Yamasaki The University of Tokyo

research subject

The DNA condensation that is the DNA conformational transition from an elongated state into a compact state has been investigated from the view point of it’s conformation, and recently attracted much attention in relation to the gene delivery as an important first step of gene therapy. Previously, however, it has not been clarified whether a DNA condensate is generated from single molecule or multi-molecule, and whether the transition is induced in continuous or discontinuous. Recent development on fluorescence video-microscopy allows us to observe the discontinuous transition behavior in a single DNA chain. In this study, the correlation between DNA conformation and the residual charge during the transition is investigated by using free solution DNA electrophoresis under fluorescence microscope.

Fujii group

Rheology of Soft Matter Restricted by Spatial Confinement Effects

 

[ Leader ]
Shuji Fujii Nagaoka University

research subject

Shear-induced phenomena observed in soft matter systems show remarkable change in viscoelasticity. One of the typical examples is a shear-induced lamellar-to-onion structural transition. As is already known, rheological properties of the shear-induced onion phase is classified into the shear-thickening and shear-thinning regime as a function of shear rate. We found that the reduction of the sample geometry also causes a shift of the rheological properties from shear-thickening viscosity to shear-thinning one. Therefore it is suggested that the spatial confinement field would be a new parameter to control the ordered phase formation of soft matter systems. In this study, we investigate the rheological dynamics and stability of the onion phase induced by shear under static and dynamic spatial confinement fields. Here, the static spatial confinement field is simply achieved by putting a limit to the size of the sample geometry. On the other hand, hydrodynamic interaction induced by doping guest components into the lamellar system will be regarded as dynamic spatial confinement field. We elucidate the origin of spatial confinement effects and develop this idea into the soft matter rheology under spatial confinement fields.

Annaka group

Order-Order and Order-Disorder Transition of Micelle Networks Composed of Lipid-Mimic Block Copolymer Induced by External Field

 

[ Leader ]
Masahiko Annaka Kyushu University

research subject

Jinnai group

Order-Order Transition of Microphase-Separated Structures in Block Copolymers Studied by Transmission Electron Microtomography

 

[ Leader ]
Hiroshi Jinnai Kyoto Institute of Technology

research subject

Kai group

Dynamics of Networks Phase Change in Liquid Crystal Elastomer

 

[ Leader ]
Shoichi Kai Kyushu University

research subject

Dynamics of Networks and Phase Change in Liquid Crystal Elastomer Swollen liquid crystal elastomer (LCE) gels show quite interesting phase changes and mechanical properties. Our dry LCEs, which are not swollen by any solvent, have only two states either a liquid crystal (LC) phase or isotropic one. Nevertheless when they are swollen with other LC solvents, complicate phase changes can be observed with temperature change. Simultaneously, big mechanical property changes and high sensitivity to external fields may be induced. Our goal of the present research subject is to understand the origin of specific electrical and mechanical properties of liquid crystal elastomers and the relation between such properties and network structures as well as swollen dynamics in LCE gels swollen with low molecular weight LCs.

Fukuda group

Numerical Calculation on the Structures and Dynamics of Liquid Crystal Systems Possessing 3-Dimensional Order, Including Blue Phases

 

[ Leader ]	[ Member ]
Jun-ichi Fukuda National Institute of Advanced Industrial Science and Technology	Makoto Yoneya National Institute of Advanced Industrial Science and Technology

research subject

The aim of our study is to investigate equilibrium and non-equilibrium properties of three-dimensional ordered structures of liquid crystal phases, such as cholesteric and smectic blue phases, by numerical simulations based on continuum theory or molecular dynamics. From the viewpoint of continuum simulations, we construct a model that properly involves important factors describing the three-dimensional order of liquid crystals, including orientational order, positional order, topological defects, and optical anisotropy. We make clear thermodynamical properties of ordered structures and the dynamics of ordering and phase transition. By molecular dynamics simulations, we investigate the relation among molecular structures, molecular interactions and three-dimensional ordered structures of liquid crystals, and the microscopic origin of structural change in response to external fields or mechanical deformations. Our targets include the response of blue phases to electric fields, the mechanism of the stabilization of blue phases due to guest components, and the elucidation of how orientational order and positional order coexist in those three-dimensional liquid crystal phases.

A03 Public Participation Research (2007-2008)

Araki group

Destabilization of Electrophoretic Motion of Charged Particles Due to Hydrodynamic Interaction

 

[ Leader ]
Takeaki Araki Kyoto University

research subject

Electrophoresis is one of the most important methods for separating colloidal particles and biological molecules such as DNA and proteins in terms of their charge. We study the electrophoresis of many particles systems by means of Fluid Particle Dynamics simulation. We observed that the particle drift velocity fluctuates in time and space, due to the hydrodynamic interaction. This velocity fluctuation is harmful for characterization of the particles, since the electrophoresis relies on the correlation between particle velocity and the charge. The aim of this study is to develop a method for suppressing the velocity fluctuation and make a non-equilibrium phase diagram of charged colloidal system under an electric field.

Takiguchi group

Direct Observation and Dynamic Simulation Analyses of Interaction Between Lipid Bilayer Membranes and Self-Organizing Peptides

 

[ Leader ]	[ Member ]	[ Member ]
Kingo Takiguchi Nagoya University	Makoto Kinoshita Kyoto University	Tamiki Umeda Kobe University

research subject

Lipid molecules spontaneously assemble to bilayer membrane in aqueous solutions. Living cells and cellular organelles are all compartmentalized by the lipid bilayer membranes and show characteristic shapes depending on their specific functions. Their shapes are quite changeable and morphological changes of cellular membranes, for example, endocytosis or exocytosis, play essential roles in cellular activities. Many proteins or polypeptides are considered to be involved in the determination of membrane morphology and function by assembling at the surface of the membranes and forming a cortex. Although already many studies have been achieved, the studies for understanding the transformation process in the membrane morphogenesis induced by those proteins are only now in progress. Liposomes, the closed lipid bilayer membrane vesicles, have been well studied as simplified models of biological membranes and used in a number of applications. Giant liposomes can be directly observed by various optical microscopies. Thus, behaviors of the bilayer membranes can be followed in the real-time. By using giant liposomes, we try to understand the mechanism of membrane morphogenesis and dynamics resulted from the interaction between two different soft matters from the life, lipid bilayers and the membrane-associate self-organizing proteins, such as the BAR, PH or polybasic domain proteins.

Miyata group

Spatio-Temporally Forcing Phase Separation of Polymer Mixtures by Light: Its Kinetics and Applications to Materials Science

 

[ Leader ]	[ Member ]
Qui Tran-Cong-Miyata Kyoto Institute of Technology	Tomohisa Norisuye   Kyoto Institute of Technology

research subject

The purpose of this project is to examine and elucidate the kinetics as well as the morphology resulting from phase separation of polymer mixtures under thermodynamically open conditions. For this purpose, photochemical reaction is used as a driving force to induce and terminate the phase separation independently from thermodynamic variables such as P, V, T. A computer-assisted irradiation (CAI) method was developed to gain spatial, temporal and spatio-temporal control of the phase separation process. Mode selection in the phase separation process will be observed and analyzed in order to establish a novel method for morphology control. The final goal is to investigate the possibilities of designing polymer materials with self-adjusting and self-generating behavior under far-from-equilibrium conditions.

Fukao group

Aging Dynamics in Polymer Glasses

 

[ Leader ]
Koji Fukao Ritsumeikan University

research subject

If a liquid is cooled down from high temperature to a temperature below melting temperature, a supercooled liquid state is obtained. The glassy state can be rearched through this supercooled liquid state under an appropriate cooling condition. This is called glass transition and the glassy state has a non-equilibrium nature. In the glassy state, aging phenomena are observed where the non-equilibrium glassy state approaches an equilibrium state and a non-equilibrium relaxation is accompanied. During aging process in the glassy states some interesting phenomena such as memory effect and rejuvenation effect are observed with measurements of ac-susceptibility. In this study, dielectric relaxation spectroscopy method is used in order to elucidate the nature of non-equilibrium relaxation phenomena during the aging process for glassy states of polymers, which is most important representative of soft matters.

Sakai group

Non-Equilibrium Structure Formation and Dynamics of Sliding Graft Copolymers

 

[ Leader ]
Yasuhiro Sakai The University of Tokyo

research subject

Polyrotaxane is a supramolecular complex in which many cyclic molecules are threaded on a linear polymer chain. The cyclic molecules can slide along and rotate around the polymer chain. "Sliding graft copolymer (SGC)" has side chains grafted onto cyclic molecules of a polyrotaxane, therefore SGC can be regarded as a graft copolymer with movable side chains. In this study we conduct theoretical and experimental research on the structure formation and dynamics of sliding graft copolymers. Especially, we focus on the effect of the mobility of the side chain on the micelle formation, microphase separation and dynamics in the external field.

Sugawara group

Introduction of Elasticity into Extend Field-Sensitive Elastica Consisting of Tubular Vesicles

 

[ Leader ]
Tadashi Sugawara The University of Tokyo

research subject

Manipulation of soft materials, e.g. giant vesicles by external stimuli has drawn attention in recent years. Although a high static magnetic field can regulate the orientation of tubular giant vesicles (tGVs) on the basis of anisotropy of diamagnetic susceptibility, direct magnetic manipulation of vacant tGVs is not plausible. We found that collagen-containing tubular giant vesicles (Col-tGVs) form characteristic curved structures in a high static magnetic field. We ascribed the formation of these structures to the curvature-elasticity potential of the tGV and the magnetic potential due to the competing diamagnetic anisotropies of collagen and the tGV. The deformed structures are sustained by polymerization of collagen inside the tGV, and the observed curved structures were well reproduced using the absolute value of diamagnetic anisotropy of Col-tGV. We are planning to make an optical attachment for the insert of a superconducting magnet in order to perform real time-observation on the deformation dynamics of Col-tGV in high magnetic field. When Col-tGV is deformed in a magnetic field the number density of the membrane molecules becomes uneven. However addition of a wedge-like molecule, e.g. cholesterol, is expected to fix this uneven membrane structure by inserting themselves in the voids of deformed membrane. Therefore we may observe some hysteretic behavior in the magnetic field-induced deformation process of non-magnetic material (Col-tGV).

Matsuyama group

Phase Separation Dynamics in Mixtures of Liquid Crystals and Colloidal Crystals

 

[ Leader ]
Akihiko Matsuyama Kyushu Institute of Technology

research subject

Colloidal dispersions take place phase transitions from a liquid to a crystalline phase with increasing the concentration of colloids. How is phase separations when these colloids are dispersed in a liquid crystalline solvent? Recently, "Liquid crystal colloids", consisting of colloidal particles dispersed in thermotropic or lyotropic liquid crystals, have been much attention for new materials and new fields in physics. Although the theoretical progress in the single-particle description of colloids dispersed in liquid crystals has been noticeable, little theoretical work exists in macroscopic morphology, phase separations, and mechanical properties. In this project, we theoretically study phase separations and dynamics in mixtures of liquid crystals and colloidal crystals. We focus on (1) phase ordering and phase separations of colloids suspended in a nematic or smectic A liquid crystalline phase and (2) the phase separation dynamics induced by an external field such as electric and magnetic fields. We aim at the creation of new dynamics where crystalization of colloids competes with orientational ordering of liquid crystals. We focus on spinodal decompositions, nucleation, and phase separations in liquid crystal colloids.

Harada group

Dynamics of Fluctuations in a Excitable Cell－Single Cell Approach－

 

[ Leader ]
Takahiro Harada University of Fukui

research subject

We investigate the nonlinear dynamics of biological cells with paying attention to fluctuations in a long timescale. We focus on cardiac muscle cells as an example. We examine the properties of spontaneous beating of these cells in timescales ranging from sub-seconds to several ten hours, in order to characterize the fluctuations inherent in their dynamics. We have already found that single isolated cardiac muscle cells exhibit intermittent fluctuations. In the present project, we aim to clarify the molecular mechanism of this peculiar fluctuations. Through this study, we will approach complex dynamics of heart beat, which has been studied in the levels of tissues and the organ, from the level of single cells. Moreover, we explore novel phenomena that appear through interplays between thermal noise and unstabilities in nonequilibrium conditions.

Nagaya group

Dynamics of Localized Structure in a Liquid Crystal Light Valve

 

[ Leader ]	[ Member ]
Tomoyuki Nagaya Oita University	Shigetoshi Nara Okayama University

research subject

The liquid crystal light valve consists of a thin sandwich structure with a photoconductor, a nematic liquid crystal layer, a dielectric mirror and transparent electrodes. When the photoconductor is locally illuminated, photo carriers are correspondingly nucleated in the photoconductor. As a result, in the area of reading side faced to the illuminated area, the voltage applied across the liquid crystal (LC) layer is increased. Then reorientation of the liquid crystal molecules takes place. When the ellipsoidally polarized light emitted from the LC layer is fed back to the photoconductor, the dependence of the liquid crystal tilt angle on the applied voltage shows bistability in several voltage ranges. Consequently, a self-organized pattern appears when the spatial distribution of the tilt angle has an inhomogeneous structure. Several kinds of self-organized patterns have been found so far. In the present study, we will focus the petal-like pattern, which appears under the pure-interferential optical feedback with spatial rotation, and the localized spot pattern, which appears under the pure-differential optical feedback. Depending on the applied voltage and the intensity of writing light, these pattern changes dynamically. By utilizing image-processing technique, we will investigate the dynamics of these patterns in detail.

A04 Public Participation Research (2007-2008)

Fujiwara group

Theoretical and Simulational Study of Soft Matter Interfaces

 

[ Leader ]	[ Member ]	[ Member ]
Susumu Fujiwara Kyoto Institute of Technology	Kiyoshi Sogo Kitasato University	Shuhei Ohnishi Toho University

research subject

In application of a computer experiment, although the simulation of structure formation and non-equilibrium dynamics of soft matter is an important subject, the essential limit is reached in the handling of discontinuous interfaces, such as phase separation and topological change of interfaces. The reason for this is taht various scales from microscopic to macroscopic are intermingled in an interface. There, a scheme of scale adaptation, such as an introduction of the transition layer by the mathematical model of an interface, is needed. Therefore, this research aims at establishment of a new simulation method also including topological change of the interface in a soft matter system. Specifically, we will clarify, on a mesoscopic scale, how the interfacial tension acts and how the interaction between elements changes in a soft matter interface by using the constant interfacial tension molecular dynamics method. Furthermore, mathematical analysis of the scale conversion is performed by the geometric theory of a curved surface, and a multi-scale simulation method only depending on a scale factor is established.

Deguchi group

Dynamics of Knotted Polymers and Statistics of Polymer Networks:A Microscopic Topological Viewpoint on the Macroscopic Behavior

 

[ Leader ]	[ Member ]
Tetsuo Deguchi Ochanomizu University	Kyoichi Tsurusaki Kanagawa Industrial Technology Center

research subject

The topology of a ring polymer is represented by a knot, which does not change under thermal fluctuations. Macrscopic properties of a material consisting of ring polymers of the same knot type may depend on the topology, i.e the knot. If it is the case, we say that it is due to topological entanglement effects. In the proposed research, we investigate several macroscopic properties of ring polymers of the same knot type mainly through simulation, and discuss how they should depend on the topology. From the dynamical and statistical mechanical viewpoints we study topological entanglement effects such as entropic repulsions among ring polymers in solution which arise from topological constraints, through computer simulations. We also study topological entanglement effects appearing in polymer networks. In the proposed research, we evaluate some universal physical quantities such as the ratio of the diffusion constants between linear and ring polymers with the same molecular weight, through numerical simulation such as the Brownian dynamics. Comparing the theoretical values with experimental values, we discuss the validity of various theoretical models for linear and circular polymers, systematically. The present research is motivated strongly by some recent developments in synthesizing ring polymers with very large molecular weights and experiments on ring polymers such as circular DNAs. For instance, the diffusion constants are measured for fluorescently labelled linear and relaxed circular DNAs with very high accuracy.

Miyazaki group

Dynamics of Gelation of Colloidal Suspension and its Rheology

 

[ Leader ]	[ Member ]
Kunimasa Miyazaki University of Tsukuba	Hiroshi Frusawa Kochi University of Technology

research subject

Colloidal suspensions form metastable structures such as gels and glasses when a strong attractive interaction is induced or the density is high. They become glassy in the high density limit, whereas the gelation is observed in the low-density and strong-attraction limit. Colloidal gels and glasses both exhibit a universal slow dynamics. Does that mean that the two distinct physical states can be understood on a common footing? How the dynamics would change in the intermediate density regime? This project aims at answering these questions by theoretical and computational methods as well as via extensive collaborations with experimental groups, with a strong emphasis on the microscopic dynamics and rheology of the systems. Understanding of these states could have important implications for arguably more complicated phenomena such as the self-assembly and protein crystallization. Specific subjects of the project include (a) to understand the interplay between phase-separation and gelation, (b)nonlinear rheology of colloidal gels, and (c) gelation of micro-phase separating systems.

Sumi group

Development of Theoretical Methods for Analysis of Polymer Behaviour in Mediums Where Large Fluctuations Exist

 

[ Leader ]
Tomonari Sumi Toyohashi University of Technology

research subject

In this study, we propose a statistical method for analysis of polymer behavior immersed in solvent where long-range density fluctuation exists. We apply this method to the following three systems: (1) polymer chain immersed in supercritical solvents near the critical point; (2) polymer chain immersed in binary fluid mixtures near the critical point of liquid-liquid phase separation; (3) polyelectrolyte immersed in aqueous solutions containing mono-valent and polyvalent salts. For the system (1), we demonstrate a universal behavior of polymer chain and a characteristic behavior of that polymer chain near the critical point, and show a unified description for the both phenomena. In the system (2), we can expect to observe various behaviors of polymer chain near the critical point because of many sets of interaction potentials in comparison with the system (1). We investigate these phenomena, and clarify the relationship between polymer behavior and solvation. In general, only salt effects are considered as solvent effects for polyelectrolyte. In this study, we employ a solvent model where water particles are considered explicitly in order to investigate self-condensation of polyelectrolyte caused by effects of salt and water.