2019年3月4日 Prof. Bruce Law

日時:2019年3月4日(月) 14:30〜16:00
場所:首都大学東京 8号館301号室
講師:Prof. Bruce Law (Kansas State University)
題目:Particles at liquid surfaces: mechanics and thermodynamics

 

要旨:Particle adsorption and self-assembly, at a liquid surface, determines the surfactant behavior of these particles in Pickering emulsions and governs the flotation process, used extensively in the mining industry, to separate valuable minerals and metals in the ground from other residual materials. The physics of particles at liquid surfaces is still incompletely understood and is a subject of continuing current interest. In this seminar we review recent developments. The physics, which is applicable, depends upon particle size. For sufficiently large particles, of order microns, surface and line interactions determine the particle behavior as required by mechanical equilibrium. For sufficiently small particles, of order nanometers, both mechanical and thermodynamic equilibrium of the particle at the liquid surface must be considered. For these nanometer-sized particles finite-size line tension effects, originating from the van der Waals interaction, are found to play an important role.

2019年2月15日 Prof. Michael Elbaum

日時:2019年2月15日(金) 11:00〜12:30
場所:首都大学東京 8号館302号室
講師:Prof. Michael Elbaum (Weizmann Institute of Science)
題目:Cellular imaging in 3D with cryo-STEM tomography

 

要旨:Cryo-electron microscopy has achieved unprecedented resolution in recent years with new technological breakthroughs. However its practice is traditionally restricted to the study of ultra-thin specimens. While tomography introduced a view in three dimensions, the thickness limitations of traditional imaging modalities remain. We have introduced the method of scanning transmission electron microscopy (STEM) for cryo-tomography of biological specimens. STEM is inherently suited to thicker samples, in some cases reaching intact cells. Moreover, the image contrast based on electron scattering can be interpreted quantitatively. The talk will describe the methodology and a number of applications to intracellular crystallization and self-assembly.

2019年1月30日 Prof. Kuo-An Wu

日時:2019年1月30日(水) 11:00〜12:30
場所:首都大学東京 8号館302号室
講師:Prof. Kuo-An Wu (National Tsing Hua University)
題目:Pattern formation theory in tackling challenges in condensed matter at the nanoscale

 

要旨:The Swift-Hohenberg equation has been widely used to model formation of patterns seen in nonlinear systems at the macroscopic scale. The phenomenological model can be recast into an atomistic continuum model, namely the phase field crystal model, to describe material systems where the self-organized patterns represent crystal lattice structures. Besides its close relation to the Swift-Hohenberg equation, the phase field crystal approach has its roots in the classical density functional theory of freezing, and it bridges the molecular simulations and macroscopic continuum models. In this talk, I will briefly discuss how the lattice pattern at the atomistic scale naturally gives rise to anisotropies in surface energies and kinetic coefficients which are main determinants of morphology of crystals at the macroscopic scale. In addition, the simple phase field crystal model is capable of describing elasticity, plasticity, and discrete dislocations that enables us to study fundamental mechanisms of nanocrystalline grain growth and grain boundary grooving. I will discuss how discrete structures, such as dislocations and grain boundaries (usually omitted in classical theory), drastically change predictions of classical theory.

2019年1月17日 Mr. Sami Al-Izzi

日時:2019年1月17日(木) 11:00〜12:30
場所:首都大学東京 8号館301号室
講師:Mr. Sami Al-Izzi (University of Warwick)
題目:Hydro-osmotic instabilities in active membrane tubes

 

要旨:We study a membrane tube with unidirectional ion pumps driving an osmotic pressure difference [1]. A pressure-driven peristaltic instability is identified, qualitatively distinct from similar tension-driven Rayleigh-type instabilities on membrane tubes. We discuss how this instability could be related to the function and biogenesis of membrane bound organelles, in particular, the contractile vacuole complex. The unusually long natural wavelength of this instability is in agreement with that observed in cells.

 

[1] S. C. Al-Izzi, G. Rowlands, P. Sens, and M. S. Turner, Phys. Rev. Lett. 120, 138102 (2018).

Mini Conference on Physical Chemistry of Molecular Assembly (Jan. 12, 2019)

Mini Conference on Physical Chemistry of Molecular Assembly

 

Date: Saturday, January 12, 2019

Place: International House, Tokyo Metropolitan University

 

Program:

10:30 - 11:15   Ulf Olsson(Lund University)

     On the kinetic stability of non-ionic surfactant vesicles

11:15 – 12:00   Tadashi Kato(Tokyo Metropolitan University)

     Shear-induced structures in lyotropic phases of nonionic surfactants

 

13:30 – 14:15   Kazuya Saito(University of Tsukuba)

     Liquid crystal study based upon entropy analyses

14:15 – 15:00   Toshiyuki Shikata(Tokyo University of Agriculture and Technology)

     Structure and dynamics of chemically modified cellulose ethers in aqueous solution

 

15:30 – 16:15   Masayuki Imai(Tohoku University)

     Morphology of vesicle aggregates

16:15 - 17:00   Shuji Fujii(Hokkaido University)

     Rheology of cholesteric blue phase

 

 

Abstracts:

Ulf Olsson(Lund University)

On the kinetic stability of non-ionic surfactant vesicles

Surfactant/lipid vesicles are closed bilayer aggregates that are interesting to understand because of their importance in several biological processes. They are often surprisingly stable, partly because of an intriguing stability against Ostwald ripening. If, in addition, fusion events are rare, a vesicle dispersion may retain its size distribution for weeks and months. For this reason, kinetic stability of vesicles is sometimes misinterpreted as thermodynamic stability. Here we will focus on vesicle (membrane) fusion and how its kinetics depends on the surfactant monolayer spontaneous curvature, H0. As model system we have studied the binary water-C10E3 (CH3(CH2)9(OCH2CH2)3OH) system, where H0 of the non-ionic surfactant monolayer can be conveniently tuned by varying the temperature.(We use the convention that curvature away from water is counted as positive, thus, H0 decreases with increasing temperature, H0≈10-3(T0-T) where T0 is the “balanced temperature” where H0=0). In the vicinity of H0=0 (here, T≈26 °C), the surfactant may form two different bilayer phases. A lamellar phase, when H0>0 (T<26 °C) and a sponge phase when H0<0 (T>26 °C). Interestingly, it is found that the lamellar phase can in excess water be fragmented into kinetically stable uni-lamellar vesicles, while the sponge phase can not. Above 26 °C vesicles spontaneously fuse and the rate increases with increasing temperature. The fact that vesicle fusion typically requires H0<0 is consistent with membrane fusion models involving the so-called stalk intermediate structure. Vesicle fusion was also studied with giant uni-lamellar vesicles using rapid confocal laser scanning microscopy.

 

 

Tadashi Kato(Tokyo Metropolitan University)

Shear-induced structures in lyotropic phases of nonionic surfactants

In the past two or three decades, much attention has been paid to shear effects on the structure of the lyotropic phase composed of amphiphiles. Among them, the most striking result may be the transition from the lamellar phase to the "onion phase" composed of multilamellar vesicles alone without excess water. Although the onion formation has been found more than 20 years ago and reported for many systems after the first report by the French group, conditions and mechanism for the transition have not yet been fully understood. In this symposium, first I will talk about our discovery of the lamellar-to-onion transition with increasing temperature and also the re-entrant (lamellar-onion-lamellar) transition with temperature variation under a constant shear rate in nonionic surfactant systems based on experiments of rheo-SALS and rheo-SAXS. Then, I will propose a theoretical expression for deformation energies stored in polyhedral onions whose temperature dependence at rest is considered to dominate the re-entrant transition. Finally, I would like to demonstrate that intermediate structures may exist between lamellar and onion not as transient but as steady states depending on temperature and shear rate based on the results of rheo-SAXS experiments.

I will briefly mention another shear effects on the inverse bicontinuous cubic phase of a nonionic surfactant which suggests possibility to control the grain refining and grain growth by changing the amplitude of oscillatory shear without using the transition from other phases.

 

 

Kazuya Saito(University of Tsukuba)

Liquid crystal study based upon entropy analyses

Expected roles of entropy, one of most macroscopic quantities, are discussed in the scope of modern material research. Analyses of entropy attributable to alkyl chains attached to hard core of liquid crystalline molecules are utilized as case studies, which give new insights about stabilization of liquid crystalline phases and aggregation modes of layered smectics.

 

 

Toshiyuki Shikata(Tokyo University of Agriculture and Technology)

Structure and dynamics of chemically modified cellulose ethers in aqueous solution

Cellulose is abundant natural resources generated by plants. Many kinds of chemically modified celluloses have been supplied. We pay attention to hydroxypropylated and methylated cellulose ethers (HpMCs) which possess high solubility in cold water such as at 10 ºC, but lose it at higher temperatures than e.g. 50 ºC. Here, we report linear viscoelastic behaviours of aqueous solutions of HpMCs and discuss the configuration of HpMC molecules in aqueous solution.

Series of HpMC samples, which have the average substitution numbers of hydroxypropyl and methyl groups of 1.9 and 0.25, respectively, for 3 hydroxy groups in each glucose unit and have the weight average molecular weights: Mw/103=20, 75, 150, 215 and 300, were dissolved into pure water over a wide concentration (c) range. Dynamic viscoelastic measurements were carried out for aqueous HpMC systems, and storage and loss moduli, G’ and G”, were determined in a frequency range: ω=10-2−102 s-1 at 10 ºC.  

Although the viscoelasticity of the systems became pronounced with increasing concentrations and molecular weights as usually observed in polymeric solutions, the determined viscoelastic parameters did not show that HpMC molecules behave as flexible polymeric chains. The c and Mw dependencies of the average modulus and relaxation time for the system were fairly corresponds to the theoretical prediction for rigid rod like particles.

 

 

Masayuki Imai(Tohoku University)

Morphology of vesicle aggregates

In this study we show the morphology transitions of adhering giant unilamellar vesicles (GUVs) induced by the changing the reduced volume of vesicles. The GUV is homogeneous single component vesicle composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). First we adhered two spherical GUVs by controlling the inter-vesicle interactions. Thereafter we decreased the reduced volume of the adhering vesicles by using thermal expansion of membranes. Depending on the reduced volume, the doublet deformed its shape and showed a unique morphology transitions. We describe the observed morphology transitions based on the competition among the bending elasticity, the surface tension, and the adhesion.

 

 

Shuji Fujii(Hokkaido University)

Rheology of cholesteric blue phase

Structure of the cholesteric blue phase is characterized by ordered alignment of the disclination lines. Numerical simulations have suggested that the alignement of the ordered disclination networks is disturbed by shearing, and break and annihilation of the disclination lines under shear induces anomalous rheological behavior. In this talk, experimental rheology on the cholesteric blue phase is presented, and we discuss how the blue phase rheology is correlated with the disclination networks.