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以上，よろしくお願いします。| Name | Title | Abstract |
|---|---|---|
| 阿部紀遥（京都大学） | Mean-field approach on the temperature dependence of solubility of nonpolar molecules in water | Solubility of nonpolar molecules in water decreases with temperature at atmospheric pressure. Little known fact is that at fixed solvent density, the solubility decreases monotonically with temperature for a wide range of temperature. To clarify the contribution of solvent structure to this behavior, we take a mean-field approach, where the average solute-solvent attraction is assumed to be independent of the temperature. The consequence is that the excess chemical potential of the solute increases linearly with kT. The kT term appears in the Boltzmann factor and its role is to lower the positive effect of the solute-solvent attraction on the solubility. Each assumption in the mean-field approximation is verified by molecular dynamics simulation. Hence, it is revealed that at fixed solvent density, the temperature dependence of the solubility is dictated by the kT term and the effect of solvent structure is negligible. |
| 天野健一（京都大学) | Measurement theory of a confined liquid structure and its correction method | A liquid structure confined between two surfaces of substrates is one of the important topics in surface science, biophysics, nanotechnology, etc. However, it is difficult for experiments to measure it, because of the confinement. In x-ray experiment, for example, the confining substrates must be thin enough for the x-ray to be possible to penetrate, and their bulk crystal structures must be well ordered. Recently, we proposed its measurement theory to overcome the restrictions. In the theory, the restrictions about the thinness and ordering are not there. The theory needs a force curve between the two surfaces, which can be obtained by using surface force apparatus, and the theory transforms it into the confined liquid structure. In the presentation, we explain the theory based on the statistical mechanics of simple liquids. The practicability of the theory is discussed by showing results of its verification tests. It is found that when the bulk number density of the liquid is low and the solvophilic properties of the substrates are not high, the theory can reproduce the confined liquid structure from the force curve. A correction method of the theory to achieve further precision is also explained. |
| 井上雅郎（九州大学大学院理学府） | Volume-fraction dependence of resistance force acting on probe particles in microrheology | We study effects of interactions between particles on resistance force acting on probe particles in microrheology. We consider a probe particle embedded into a colloidal suspension. When the probe particle is pulled at a constant velocity, it is subjected to resistance force due to collision with colloidal particles. We obtain the concentration distribution of colloidal particles by solving numerically the differential equation of the time-dependent density functional theory. This theory has been successful in describing the dynamics of simple liquids and colloidal dispersion systems. The resistance force is determined by the concentration distribution around the probe particle. Here, for interactions between colloidal particles, we consider two cases: hard-sphere interactions and no interactions. By comparing the calculated results of two cases, we clarify effects of hard-sphere interactions between colloidal particles on the resistance force. The results show that the effects of the interactions vary depending on volume fractions of colloidal particles for slow velocities of the probe particle. The resistance force decreases because of the interactions for small volume fractions, while it increases for large volume fractions. In contrast, for fast velocities, the resistance force increases because of the interactions for small and large volume fractions. |
| 江波戸佑来（愛媛大学理工学研究科） | “A bridge correction in Ornstein-Zernike theory to resolve the inconsistency in pressure between virial and compressibility routes for Lennard-Jones fluids” | One of the problems in approximated Ornstein-Zernike theory is the inconsistency in pressures, which can depend on the routes actually used to evaluate them. We propose a bridge function to resolve this inconsistency for Lennard-Jones fluids. Apparently, the proposed bridge function has an effect to enlarge the particle size, which can be regarded as an adjustable parameter. Thanks to this apparent effect, the virial pressures calculated from HNC and KH closures are significantly reduced through the correction of the location of first rising region in radial distribution function. The compressibility pressures are also corrected properly with the proposed bridge function since it reduces the isothermal compressibility. The adjustable parameter involved in the bridge function is determined so that the virial and compressibility pressures coincide with each other. We also report the excess internal energy and excess chemical potential calculated under the proposed bridge function. |
| 金子敏宏（東京理科大学理工学部) | Elevation/depression mechanism of melting points of solid confined in nanopores | To realize thermal energy storage system using solid-liquid phase-change materials, it is important to control their melting points. It is well known that the melting points in nanoporous media are different from bulk, though the mechanism of melting temperature change is not fully understood. Here, to predict melting points of materials confined in nanoporous media, we verify the Gibbs-Thomson equation. In our previous studies, the melting points of argon and water confined in nano-size space between two parallel walls were determined. In this study, we derive melting points through Gibbs-Thomson equation using surface tension and latent heat and compare to the melting points directly determined by molecular dynamics simulations. |
| 川畑雄一（九州大学） | Solute Size Dependence of Preferential Interaction in Hard-Sphere Mixture | The crowders' effects on the stability of a protein are often discussed in the viewpoint of the preferential interaction. If the excluded volume effect based on repulsive interactions is dominant in the system, it is expected that the chemical potential of a protein decreases due to the preferential solvation of large crowders. To evaluate this effect quantitatively, we studied the chemical potential in hard-sphere mixture systems which have no attractive interaction. We investigated the system which contains solvent (small-sized sphere), crowders (medium-sized sphere), and a solute (large-sized sphere), varying the composition of the mixture at constant pressure. For numerical analysis, some analytical equations of state (EOSs) and the Fundamental Measure Theory WhiteBear version mark II with Kirkwood-Buff theory were used. The main conclusion obtained from the Fundamental Measure Theory is that the solvation free energy can be decreased by addition of the cosolvent due to the depletion interaction between cosolvent and solute when these spheres are large enough. However, the analytical EOSs we used here failed to predict the correct behavior of preferential solvation. These failures are due to the incorrect dependence of the second virial coefficients of osmotic pressure on the diameters of the solute. |
| 澤山拓斗（九州大学理・化） | Aggregation behavior of macroanions in an electrolyte solution | Although macroanions repel each other in a dilute electrolyte solution, effective attraction between macroanions is observed in biological systems, such as in the assembly of G-actins. Previous our study suggests that the effective attraction is mediated by cations. As the concentration increases, the attraction becomes stronger. However, the attraction becomes maximum at an electrolyte concentration, and becomes weaker as the electrolyte concentration increases more in spite of increase of mediators. This reentrant behavior is shown not only by experimental result but also by previous calculation by using integral equation theory. In our calculation of the effective potential, the system has only two macroanions, namely dilute limit. However, the experiment indicate that the aggregation behavior of negatively charged proteins is not depends only on the electrolyte concentration but also on the protein concentration. To discuss the aggregation behavior of macroanions, we carried out Monte Carlo simulations on the basis of the effective interaction given by the integral equation theory. Taking account of cation-adsorption on the macroanions, we obtain the aggregation phase diagram which is similar to the experimental results for acidic proteins. |
| 徳永健（工学院大学教育推進機構） | Energy Conversion Efficiency of Solvation Motor driven by a Reaction on the Motor Surface | Energy conversion efficiency of the "Solvation Motor" is investigated by molecular dynamics simulations. In this model, a reaction on the motor surface is transformed into a motion of the motor particle by the change in the solvation structure around the reaction site. Pulling the motor with a constant velocity, contribution of the surface reaction to the work by solvents is estimated from the difference between the work with a reaction and the work without a reaction. Energy conversion efficiency of the solvation motor with finite reaction time is around 1% at the maximum. Dependence of the efficiency on the motor size and system size is also discussed in the presentation. |
| 西山桂（島根大学教育学部) | Size control of rare-earth nanoparticles by means of homogeneous precipitation method in the aqueous phase | We discuss synthetic methods and characterization for size-controlled rare-earth oxide nanoparticles by surfactant-assembly, where the surfactant-micelle dimension in the aqueous phase is proved to determine the particle size. We report that microscopic interactions between the hydrophilic moiety of the surfactant and the raw material of the nanoparticle play a crucial role for the particle size as a product. |
| 野村遥子（筑波大学大学院数理物質科学研究科) | Lamellar repeat distances of charged phospholipid membranes dependent on charges of added co-ions | The lamellar repeat distances of negatively charged phospholipid membranes (DOPS) were measured using a small angle X-ray diffraction, while adding NaCl, Na2SO4 or Na3PO4. The lamellar repeat distances were smaller with the anion having smaller absolute charge under the same concentration of the cation. On the other hand, DLVO theory predicts that an anion with smaller absolute charge gives the larger distance. In this presentation, we focus on entropy of ions, the number of which is different among samples under the same concentration of the cation. We discuss the experimental results while considering the contribution of the entropy gain of anions released from intermembrane water layers to the bulk in addition to the classical DLVO potential. |
| 福留拓也（九州工業大学） | An analytical expression for the direct correlation function of a hard-sphere liquid derived from the extended scaled particle theory II. | We have proposed an analytical expression of the direct correlation function for a hard-sphere liquid through the solvation free energy for a pair of hard-spheres as a solute derived from the extended version of scaled particle theory (XSPT) instead of using iterative calculations with some closure. The solvation free energy has an analytical expression given by the XSPT that treats solvation of an arbitrary shaped particle into a hard-sphere liquid. In this work, we have tried to enhance accuracy in three-dimensional numerical Fourier transforms of c(r) by using the analytical three-dimensional Fourier transform of a step function, because c(r) for a hard-sphere system has a step discontinuity at r=σ. The radial distribution functions with packing fractions up to 0.5 quantitatively agree with the Monte Carlo simulation results better than the Percus–Yevick equation method under equivalent numerical conditions. |
| 安冨翔太（九州大学院理) | The impact of molecular-weight dependent adsorption of polyethylene glycol on two-state transition of myoglobin | We have investigated the impact of molecular-weight dependent adsorption of polyethylene glycol (PEG) on two-state transition of myoglobin (Mb). We found that the denaturation of Mb occurs at ~81℃ in Mb and Mb + PEG (20000, 35000) solutions, whereas Mb + PEG(6000, 10000) solutions show two-step transitions in the transition temperature curve. |
| 山下拓海（九州大学院理) | Dependence of Effective Potential of Mean Force between Negatively Charged Colloidal Particles Immersed in an Electrolyte Solution on Charge of Small Anion | The dependence of effective interaction between charged colloidal particles on electrolyte concentration is often explained by using DLVO theory. The DLVO potential is constructed of the van der Waals attraction and the electronic double layer repulsion. In the context of the DLVO theory (or Poisson–Boltzmann theory), the dependence on the charge of co-ion (with the same charge as the colloid particles) is not discussed explicitly. There are some experiments on the charge dependence. Yoshikawa et al. found that when various kinds of sodium salts are added to DNA, smaller valences of anion induce the aggregation of DNA. Hishida et al. showed that aggregation of charged phospholipid membranes also have the same tendency. Here, we calculated the dependence on the charge of co-ion by using HNC-OZ theory to discuss the dependence because we can take account of the dependence in this theory. Our results agree with experimental results, qualitatively. |
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