Papers by Mitsuhiro Shibayama
Macromolecules, Dec 28, 2015
We report a high-toughness ion gel with a nearly ideal polymer network prepared in an imidazolium... more We report a high-toughness ion gel with a nearly ideal polymer network prepared in an imidazolium-based aprotic ionic liquid (aIL) with a controlled solution pH. We formed the ion gel from tetra-armed poly(ethylene glycol) (TetraPEG), i.e., an A–B-type cross-end coupling reaction of two different TetraPEG prepolymers. To complete this A–B-type reaction, we needed to optimize the reaction rate such that the two TetraPEGs were mixed homogeneously, which strongly depends on the pH or [H+] in the aIL solution. To control solution pH, we established a “pH-buffering IL” by adding an imidazolium-based protic IL (as a proton source) and its conjugated base to the solvent aIL. We demonstrated that the pH-buffering IL exhibits a successful pH-buffering effect to maintain a constant pH (≈16.2, apparent value) during the gelation reaction. From a kinetic study, we found that the gelation reaction undergoes a simple second-order reaction of the two TetraPEGs in the pH-buffering IL. The gelation rate constant, kgel, in...
Journal of Solution Chemistry, Oct 1, 2013
ABSTRACT Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueo... more ABSTRACT Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueous solution were investigated by small-angle neutron scattering (SANS) from the viewpoint of alkyl chain length, n, and anions (Cl−, Br− and trifluoromethanesulfonate, $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ). In [C4mIm+]-based IL systems, no noticeable SANS intensity was observed for all of the systems examined here, although aqueous [C4mIm+][ $ {\text{BF}}_{4}^{ - } $ ] solutions show a significant SANS profile originating from concentration fluctuations in the solution (Almasy et al. J Phys Chem B 112:2382–2387, 2008). This suggests that [C4mIm+][Cl−], [C4mIm+][Br−] and [C4mIm+][ $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ] homogeneously mix with water, unlike the [C4mIm+][ $ {\text{BF}}_{4}^{ - } $ ] system, due to preferential hydration of the ions. In the case of the Cn mIm cations with longer alkyl chain lengths (n = 8 and 12), SANS profiles were clearly observed in the aqueous solutions at IL concentrations of C IL > 230 and 20.0 mmol·dm−3, respectively. For aqueous [C8mIm+][Br−] solutions, the asymptotic behavior of the scattering function varied largely from I(q) ~ q −2 to ~q −4 with increasing C IL, indicating that the solution changes from an inhomogeneous mixing state to a nano-scale micelle state. Aqueous [C12mIm+][Br−] solutions show a typical SANS profile for micelle formation in solution. It was found from a model-fitting analysis that the structure of the [C12mIm+][Br−] micelle is ellipsoidal, not spherical, in solutions over the C IL range examined here.
Macromolecules, Jun 15, 2017
We report a new approach for investigating polymer structures in solution systems, including poly... more We report a new approach for investigating polymer structures in solution systems, including polymer− solvent interactions at the molecular level. The solvation structure of poly(benzyl methacrylate) (PBnMA) in an imidazolium-based ionic liquid (IL) has been investigated at the molecular level using high-energy X-ray total scattering (HEXTS) with the aid of all-atom molecular dynamics (MD) simulations. The X-ray radial distribution functions derived from both experimental HEXTS and theoretical MD (G exp (r) and G MD (r), respectively) were in good agreement in the present PBnMA/IL system. The G(r) functions were successfully separated into two components for the interand intramolecular contributions. Here, the former corresponds to polymer solvation (or polymer−solvent interactions) and the latter to polymer structure, such as conformation and interactions between side chains (benzyl groups) in PBnMA. The intermolecular G MD inter (r) revealed that the side chains are preferentially solvated by imidazolium cations rather than anions. On the other hand, the intramolecular G MD intra (r) suggested that PBnMA is also stabilized by interactions among the aromatic side chains (π−π stacking). Thus, polymer (benzyl group)− cation interactions and benzyl group stacking within a PBnMA chain coexist in the PBnMA/IL system to give a more ordered solution structure. This behavior might be ascribed to negative mixing entropy in the solution state, which is key to the lower critical solution temperature (LCST)-type phase behavior in the PBnMA/IL solutions.
Journal of the Physical Society of Japan, Nov 15, 2007
ABSTRACT The effect of adding sodium tetraphenylborate (NaBPh4) on a LCST type phase separation o... more ABSTRACT The effect of adding sodium tetraphenylborate (NaBPh4) on a LCST type phase separation of a mixture of D2O and 3-methylpyridine is investigated by visual observation and small-angle neutron scattering (SANS). In the case that the amount of salt is smaller than 50 mM, the mixture colors below the phase separation temperature. When the amount of salt is increased, the phase separation disappears and a single peak profile is observed at finite-Q by SANS. These results indicate that a periodic structure is induced in one phase region by the addition of NaBPh4.
Macromolecules, Mar 1, 1986
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Macromolecules, Oct 21, 2016
We investigated pressure effects on the lower critical solution temperature (LCST)-type phase beh... more We investigated pressure effects on the lower critical solution temperature (LCST)-type phase behavior of a thermoresponsive polymer in an ionic liquid (IL) solution. The cloud point temperature of the IL solution increased monotonically with pressure, which was quite different from that of conventional aqueous polymer solutions reported in previous work, which exhibited a convex-upward-type pressure dependence. We compared the IL and aqueous systems and concluded that the difference results from their solvation mechanisms. Dynamic light scattering (DLS) measurements showed an appearance of a slow mode (corresponding to aggregation) in addition to the fast mode (corresponding to molecular dispersion) at the cloud point pressure, indicating an onset of pressure-induced phase separation. This work contributes to the fundamental understanding of the phase behavior of polymers in IL systems under high pressure.
Journal of Oleo Science, 2017
Introduction Research into microemulsions, micelles, vesicles, and liposomes with appropriate sur... more Introduction Research into microemulsions, micelles, vesicles, and liposomes with appropriate surfactants, lipids, and amphiphiles are important for the fundamental understanding of emulsion properties. Basic assemblies and micro/nanostructures have received increasing attention in recent studies in the field of nanoscience and nanotechnology 1 4. Microemulsions are thermodynamically stable, transparent, isotropic solutions with particle sizes ranging from 5 to 100 nm. They are formed by the spontaneous self-assembly of hydrophobic and hydrophilic parts of surfactant molecules. In contrast to macroemulsions, made by mechanical stirring, which are thermodynamically unstable, microemulsions have a wide range of applications, including pharmaceutical, cosmetics, oil recovery, and reaction media 5. For applications of microemulsions in foods, however, many surfactants are not permissible. More importantly, solubilization of long-chain triglycerides LCT , such as soybean oil, is more difficult to achieve than for lipids those with short or medium length triglycerides. Polyglyceryl esters PGEs are important non-ionic surfactants with various applications in the cosmetic, food, and pharmaceutical industries 6. The defining feature of PGEs is a large hydrophilic group in the molecule. They have been known since the beginning of the twentieth century and their amphiphilic character enables their use in the stabilization of various
Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2016
We investigated the aggregation behavior of star-type trimeric surfactants (3C 12 trisQ) with a h... more We investigated the aggregation behavior of star-type trimeric surfactants (3C 12 trisQ) with a hydrocarbon chain length (n) of 12 in sodium salicylate (NaSal) aqueous solution at various surfactant (C D) and salt concentrations (C S) using small-angle X-ray scattering (SAXS) and rheological measurements. At a low surfactant concentration (C D = 7 mM), 3C 12 trisQ aggregates in solution evolved from ellipsoidal micelles, to rodlike or wormlike micelles and finally to multi-lamellar vesicles (MLVs) with increasing C S. In contrast, at higher surfactant concentrations (C D = 14 and 28 mM), we did not observe vesicle formations of 3C 12 trisQ because 3C 12 trisQ were insoluble in solution at higher NaSal concentrations. The structural transitions of the 3C 12 trisQ aggregates strongly depended on both C S and C D. We also compared the MLV structure formed by 3C 12 trisQ with that formed by gemini-type surfactants (12-2-12). The repeat distance of the 3C 12 trisQ MLV (33.95 Å) was remarkably larger than that of the 12-2-12 (22.36 Å). We found that introducing spacer chains, i.e., from dimeric to trimeric surfactants, caused a decrease in NaSal concentrations at which micelle-to-vesicle transitions were observed.
Macromolecules, Mar 1, 1986
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bioRxiv (Cold Spring Harbor Laboratory), Feb 23, 2022
Based on our previous discovery of non-diffusive topologically frustrated dynamics in a charged s... more Based on our previous discovery of non-diffusive topologically frustrated dynamics in a charged system where electrostatic interactions between the charged guest and the charged host gel play a role (
Hamon, 2011
A review of investigations and upgrades during the past decade are presented for the small-angle ... more A review of investigations and upgrades during the past decade are presented for the small-angle neutron scattering spectrometer SANS-U owned by the Institute for Solid State Physics, The University of Tokyo at the research reactor (JRR-3) of the Japan Atomic Energy Agency (JAEA), Tokai, Japan. Among the two major upgrades of the SANS-U was highlighted the second upgrade carried out during 2008-2010. This includes the achievement of the increase of the incident beam flux by 3.2 times and of the lowermost Q vector to 3.8 x 10-4 Å-1 owing to an installation of focusing lenses and a high-resolution position sensitive detector consisting of a cross-wired position sensitive photomultiplier tube combined with a ZnS/ 6 LiF scintillator on the SANS-U. The versatility of SANS-U is demonstrated by a variety of accessories and various types of scientific hot topics, including high-pressure experiments, Rheo-SANS, and deformation studies on tough gels, etc.
Nuclear Instruments and Methods in Physics Research, Feb 1, 2009
We have proposed a Versatile Inelastic Neutron Spectrometer (VINS) for the spallation neutron sou... more We have proposed a Versatile Inelastic Neutron Spectrometer (VINS) for the spallation neutron source at the Materials and Life Science Facility (MLF), Japan Proton Accelerator Research Complex (J-PARC). VINS is a direct-geometry Fermi chopper spectrometer designed to provide considerably high neutron flux with moderate energy and Q resolutions. VINS is characterized by its wide energy and Q range (0.5 < ΔE < 1000 meV and Q< 40 Å-1 at ΔE = 1000 meV), enabled by an array of detectors covering large solid angle [-30 < 2θ < 130 degrees horizontally and-30 < < 30 degrees vertically (2.8 Sr)]. Monte-Carlo ray-tracing simulation estimates the sample position neutron flux as high as roughly 1x10 6 neutrons/cm 2 /sec for the ΔE/E i ~ 5% mode at E i = 10 meV. With these wide E-Q coverage and high neutron flux, VINS will be one of the most efficient and versatile inelastic spectrometers at J-PARC. Target science ranges from conventional solid-state physics, such as highly correlated electron systems, frustrated magnets and relaxors, to rather interdisciplinary areas, exemplified by glasses, quasicrystals, polymers and liquids. A particular focus is placed on extreme sample environments; high-magnetic-field and high-pressure environments are planned.
International Journal of Biological Macromolecules, Nov 1, 2021
The present study aimed to investigate the thermal- and pH-dependent gelation behavior of gelatin... more The present study aimed to investigate the thermal- and pH-dependent gelation behavior of gelatin/HPMCP blends using ultraviolet (UV) spectrophotometry, viscoelasticity, and dynamic light scattering (DLS). We found that the release of lisinopril from gelatin/HPMCP gels can be inhibited at low pH. UV spectrophotometric analysis showed that pH had a significant effect on the transparency of aqueous HPMCP systems and gelatin/HPMCP gels. The viscoelastic patterns of gelatin/HPMCP at pH 4.6 considerably differed from those of gelatin/HPMCP at pH 5.2 and 6.0. DLS measurements showed that HPMCP molecules in low concentrations underwent strong aggregation below pH 4.8. Such HPMCP aggregation induces a physical barrier in the matrix structures of the gelatin/HPMCP gels, which inhibits the drug release at pH 1.2. This hydrogel delivery system using polymer blends of gelatin/HPMCP can be used in oral gel formulations with pH-responsive properties.
ECS Meeting Abstracts
In order to improve the reaction efficiency of fuel cells, the structure of carbon and ionomer af... more In order to improve the reaction efficiency of fuel cells, the structure of carbon and ionomer affecting electronic and proton conduction and the distribution of voids affecting oxygen diffusion and drainage have been studied to find the guideline for the optimum structure of the catalyst layer. In this study we are developing a method to evaluate the dispersed structure of carbon and ionomer and the thickness of the ionomer layer by using the small and wide angle neutron scattering instrument, TAIKAN at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The dependence of ionomer-to-carbon weight ratio of small-angle neutron scattering (SANS) cross section of the solid carbon catalyst layer and the hollow carbon catalyst layer was evaluated comparatively. Furthermore, the relative humidity dependence of SANS cross section of the solid carbon catalyst layer and the hollow carbon catalyst layer was also evaluated by us...
Polymer Preprints, Japan, 2005
Dynamically crosslinked gels are appealing materials for applications that require time-dependent... more Dynamically crosslinked gels are appealing materials for applications that require time-dependent mechanical responses. DNA duplexes are ideal crosslinkers for building such gels because of their excellent sequence addressability and flexible tunability in bond energy. However, the mechanical responses of most DNA gels are complicated and unpredictable despite the high potential of DNA. Here, we demonstrate a DNA gel with a highly homogeneous gel network and well-predictable mechanical behaviors by using a pair of star-polymer-DNA precursors with presimulated DNA sequences showing the two-state transition. The melting curve analysis of the DNA gels reveals the good correspondence between the thermodynamic potentials of the DNA crosslinkers and the presimulated values by DNA calculators. Stress-relaxation tests and dissociation kinetics measurements show that the macroscopic relaxation time of the DNA gels is approximately equal to the lifetime of the DNA crosslinkers over four order...
Macromolecules, 2020
Nafion is a fluorocarbon polymer, commonly used as a proton exchange membrane in fuel cells becau... more Nafion is a fluorocarbon polymer, commonly used as a proton exchange membrane in fuel cells because of its excellent thermal and mechanical stabilities. However, the basic properties of Nafion, such as its nanostructures and rheological behavior, remain unclear because the morphology of this material is highly sensitive to its processing history. The present work involved a systematic analysis of both the structural and rheological properties of Nafion dispersions carefully prepared using a standard procedure, ranging from dilute (0.1 wt %) to highly concentrated (30 wt %) conditions. Small-angle X-ray scattering confirmed the cylindrical structure of Nafion in dispersion and the unique interactions of Nafion particles acting as polyelectrolytes. Three different scaling relationships involving the zero-shear viscosities of the Nafion dispersions were determined for specific concentration regimes. However, at the upper concentration limit of approximately 30 wt %, the viscosity greatly deviated from these scaling relationships and significant shear thinning was observed. Simultaneous analyses using rheology and small-angle neutron scattering determined fully isotropic spatial correlations on a length scale of less than 60 nm, even when high shear was applied. These results indicate a tightly entangled local structure and the presence of large yet weakly interacting domains that are responsible for the macroscopic shear thinning behavior.
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Papers by Mitsuhiro Shibayama