Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Knotting in a polymer chain was investigated by observing the chain expansion process from a collapsed chain for the solution of poly(methyl methacrylate)(PMMA) with M_w = 1.22 × 10⁷ in the mixed solvent tert-butyl alcohol + water(2.5 vol%). Because of very slow phase separation in the solution the chain collapse after a temperature drop and chain expansion after a jump were determined by static light scattering. PMMA chain was shown to collapse rapidly to an unknotted globule, which subsequently contracted slowly to a knotted globule. The chain expansion process from the knotted globule was dominated by the chain compactness and the degree of knotting of the initial globule. A complete chain expansion from a heavily knotted globule often required a very long time indicating an existence of long-lived knots. The chain expansion from the unknotted globule occurred too fast to be followed by scattering experiment.

DOI： 10.1016/j.polymer.2019.06.007

Language：English   Publishing type：Research paper (scientific journal)  

Poly(N,N-dimethylacrylamide)-clay nanocomposite gels (NC gels) with patterned network-chain density were prepared by photoinitiated radical polymerization with photomasks. The exposed region of the obtained gels showed a higher swelling ratio and lower elastic modulus than the masked region, although these regions had the same weight composition. A stripe-patterned gel prepared using a photomask with many slits of several hundred micrometers wide exhibited mechanical anisotropy: the elastic modulus in the direction parallel to the slits was higher than that in the perpendicular direction.

DOI： 10.1007/s00396-019-04486-6

Language：English   Publishing type：Research paper (scientific journal)  

When biopolymer solutions come in contact with a coagulation bath containing a gelling factor such as ions, chemical crosslinkers, and pH conditioners, diffusion of the gelling factor through the contact interface into the polymer solutions induces gelation, which proceeds gradually in a direction along the diffusion of the gelling factor. In this directional gelation process, characteristic structures are frequently formed in the biopolymer gels. This review presents general features of the structure formation by the diffusion of the gelling factors and some specific examples for typical biopolymers.

DOI： 10.17106/jbr.32.27

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

UV-crosslinked gelatin nanogel was prepared without using chemical crosslinking agents and its thermoresponsive behaviors were investigated. The particle size of the nanogels decreased on heating, which is attributed to the helix-to-coil transition of gelatin. On the other hand, the increase in the particle size on cooling was not observed in the quiescent solutions, but was noticeably accelerated by the application of shear stress.

DOI： 10.17106/jbr.32.15

Language：English   Publishing type：Research paper (scientific journal)  

A nonwoven fabric of Konjac glucomannan (KGM) for the adsorption of tannin was fabricated by using electrospinning and then followed by deacetylation with alkaline solution. To analyze the adsorption dynamics of tannin, the time course of the adsorption of tannin on the nonwoven KGM fabric was measured by immersing the fabric in tannin solution at different concentrations of tannin and amounts of the fabric. The initial and late stages of the adsorption behavior could be expressed, respectively, by using a diffusion-limited equation and a stoichiometric equation. A discussion on the dependence of the control parameters on the adsorption behavior is presented. The results represent the first step to provide an effective adsorption procedure for tannin in the use of modified KGM fabric.

DOI： 10.1039/c8sm00123e

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Curdlan, a microbial polysaccharide, forms a multi-layered gel consisting of four layers with different turbidity when its alkaline solution is dialyzed against aqueous solutions containing Ca²⁺ (diffusion-set gel). The present study clarified the microstructure of each layer of the diffusion-set Curdlan gel by small-angle X-ray scattering (SAXS) and small-angle light scattering (SALS). The SAXS data showed that Curdlan chains assume a helical ordered conformation in the gel and that the gel consists of the fibrils formed by the association of Curdlan chains and the aggregates of fibrils. The SAXS results also indicated that the gelation is induced by the formation of a network of Ca²⁺-cross-linked fibrils in the outer region of the gel, whereas by the network formation of the aggregation of fibrils in the neutralization process in the inner region of the gel. A structural anisotropy of the gel was investigated by analysis of two-dimensional SAXS images, showing that the fibril is oriented circumferentially in the outer region of the cylindrical gel, whereas it is oriented randomly in the inner region of the gel. The SALS data showed that a characteristic length of an inhomogeneous structure in the turbid layers is of the order of micrometers. The observed spatial variation of the microscopic structure is caused by the difference in the paths of pH and [Ca²⁺] traced in the gelation process.

DOI： 10.1016/j.carbpol.2016.08.061

Language：English   Publishing type：Research paper (scientific journal)  

Dilute suspensions of charged colloidal particles with a short-range attraction and long-range repulsion can exhibit a variety of arrested states. In many applications using suspensions of charged nanoparticles, the optimization of the process requires the understanding of the mechanism underlying the stability and the rheological properties of the suspensions. In an attempt to clarify the solidification mechanism for dilute suspensions of tin dioxide (SnO₂) nanoparticles, we present dynamic viscoelasticity, dynamic and static light scattering, and small-angle X-ray scattering experiments on a SnO₂ nanoparticle suspension with a nanoparticle concentration of 25.0 wt % (volume fraction φ = 0.045). The behaviors of the observed dynamic and static structure factors reveal that the aging of SnO₂ nanoparticles is Wigner glassy rather than gel-like.

DOI： 10.1021/acs.langmuir.5b03310

Language：English   Publishing type：Research paper (scientific journal)  

Molecular orientation in anisotropic gels of chitosan, Curdlan and DNA obtained by dialysis of those aqueous solutions in gelation-inducing solutions was investigated. In this diffusion method (or dialysis method), the gel formation was induced by letting small molecules diffuse in or out of the polymer solutions through the surface. For the gels of DNA and chitosan, the polymer chains aligned perpendicular to the diffusion direction. The same direction of molecular orientation was observed for the Curdlan gel prepared in the dialysis cell. On the other hand, a peculiar nature was observed for the Curdlan gel prepared in the dialysis tube: the molecular orientation was perpendicular to the diffusion direction in the outermost layer of the gel, while the orientation was parallel to the diffusion direction in the inner translucent layer. The orientation parallel to the diffusion direction is attributed to a small deformation of the inner translucent layer caused by a slight shrinkage of the central region after the gel formation. At least near the surface of the gel, the molecular orientation perpendicular to the diffusion direction is a universal characteristic for the gels prepared by the diffusion method.

DOI： 10.1016/j.carbpol.2014.03.012

Language：English   Publishing type：Research paper (scientific journal)  

Dilute solutions of poly(methyl methacrylate) in some polar solvents show very slow phase separation and remain transparent for long time periods below the cloud point. Because of this slow phase separation, both chain collapse (coil-globule transition) and aggregation were studied systematically with light scattering. In this review, recent findings on chain collapse and aggregation in dilute solutions below the h-temperature are summarized.

DOI： 10.1038/pj.2014.39

Language：English   Publishing type：Research paper (scientific journal)  

It was more than 50 years ago that an appearance of birefringence in alginate gels prepared under cation flow was reported for the first time, however, the anisotropic structure of the alginate gel has not been studied in detail. In the present study, anisotropic Ca-alginate gels were prepared within dialysis tubing in a high Ca²⁺-concentration external bath, and optical and small-angle X-ray scattering (SAXS) measurements were performed to characterize the structure of the gel. The observations of the gel with crossed polarizers and with circular polarizers revealed the molecular orientation perpendicular to the direction of Ca²⁺ flow. Analyses of the SAXS intensity profiles indicated the formation of rod-like fibrils consisting of a few tens of alginate molecules and that the anisotropy of the gel was caused by the circumferential orientation of the large fibrils. From the observed asymmetric SAXS pattern, it was found that the axis of rotational symmetry of the anisotropic structure was parallel to the direction of Ca²⁺ flow. The alignment factor (A_f) calculated from the SAXS intensity data confirmed that the orientation of the fibrils was perpendicular to the direction of Ca²⁺ flow.

DOI： 10.1021/bm200223p

Language：English   Publishing type：Research paper (scientific journal)  

Alginate gels formed by diffusion of calcium ions into solutions of sodium alginate were found to exhibit optical anisotropy depending on preparation conditions. When observed under crossed nicols, the anisotropic alginate gels showed a birefringence pattern which is characteristic of radial orientation of polymer chains. Calcium alginate gels were prepared from different concentrations of sodium alginate and calcium ion, and the conditions for formation of the anisotropic gels were determined. The gel-formation process was measured by monitoring the development of the birefringent layer and was compared with the model in which the diffusion of calcium ions dominates gel formation.

DOI： 10.1007/s12573-009-0004-1

Language：English   Publishing type：Research paper (scientific journal)  

The rates of chain aggregation of poly(methyl methacrylate) (PMMA) in acetonitrile (AcN) and in the mixed solvent of AcN+water (10 vol %) were determined by static light scattering and compared with the rates of chain collapse. Dilute solutions of PMMA with the molecular weight mw =6.4× 106 and in the concentration range of (0.8-5) × 10-4 0.3em g/cm3 were quenched below the cloud point, and the weight-average molecular weight Mw and z -average square radius of gyration S2 z for clusters of PMMA chains were measured as a function of the time t after the quench and the concentration c. The measurement of chain aggregation was carried out up to the cluster size of Mw mw ∼30, which required time periods of hours to several days depending on the concentration and solvent. The chain aggregation in AcN+water occurred much faster than that in AcN. The growth of clusters in both the solvents was represented by the exponential function as Mw ∼ egct and S2 z ∼ ehct, where g and h represent the intrinsic rate of chain aggregation. The ratio σ of the intrinsic rate in AcN+water to that in AcN was estimated to be 9 by taking a rough average of the ratios 9.4 obtained from g and 8.8 from h. This value is comparable to the ratio 11 of the rate of chain collapse of PMMA in AcN+water (10 vol %) to that in AcN. This close value of the ratios indicates that the nature of solvent would affect the rates of chain collapse and chain aggregation through a similar mechanism.

DOI： 10.1103/PhysRevE.78.041802

Language：English   Publishing type：Research paper (scientific journal)  

The molecular weight and solvent dependences of the characteristic time of chain collapse were studied for poly(methyl methacrylate) (PMMA) of the molecular weight Mw =6.4× 106 and 1.14× 107 in pure acetonitrile (AcN) and in the mixed solvent of AcN+water (10 vol %). The size of PMMA chains was measured as a function of the time after the quench by static light scattering and the chain collapse processes were expressed by the plot of the expansion factor α2 vs ln t. The chain collapse in the mixed solvent AcN+water (10 vol %) was found to occur much faster than that in pure AcN, though the measurement of the former collapse process required several hours. In order to make a comparison between the rates of chain collapses, the fast chain collapse process was superposed on the slow one by scaling the time of the fast process as γt. The scale factor γ was determined by comparing the chain collapse processes of nearly the same equilibrium expansion factor with each other. Accordingly, the superposition of the collapse for Mw =6.4× 106 on that for Mw =1.14× 107 yielded γm =4.0±0.6 for the process in AcN+water and 5.5±0.6 in AcN. The superposition of the chain collapse process in AcN+water on that in AcN yielded γs =9.5±1.4 for Mw =6.4× 106 and 12.0±1.8 for Mw =1.14× 107. This analysis suggests that γm and γs are constant independent of each other. Thus, by assuming the molecular weight dependence of γm ∼ Mz, the characteristic time τexp of chain collapse was conjectured as τexp ∼κ Mz, where κ reflects the nature of solvent species. The ratio of κ for PMMA in AcN to that in AcN+water is given by γs. The exponent was estimated to be z=2.4±0.7 for AcN+water and 3.0±0.7 for AcN. These values are compatible with the theoretical prediction z=3 based on a phenomenological model, though the observed characteristic times are longer by several orders of magnitude than those of the theoretical prediction.

DOI： 10.1063/1.2715596

Language：English   Publishing type：Research paper (scientific journal)  

The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight M _w=1.05×10⁷ in the mixed solvent of tert-butyl alcohol+water (2.5 vol%). In the chain-collapse process after a quench from the θ temperature to a temperature T₁, the temperature was changed from T₁ to T₂ at the time t₁ after the quench and returned to T₁ at the time t₁+t₂. In the three stages at T₁, T₂, and T₁, measurements of the mean-square radius of gyration of polymer chains were carried out by static light scattering and the chain-collapse process was represented by the expansion factor as a function of time. An effect of chain aggregation on the measurements was negligibly small because of the very slow phase separation. For the negative temperature perturbation (T₁>T₂), the chain-collapse processes observed in the first and third stages were connected smoothly and agreed with the collapse process due to a single-stage quench to T₁. A memory of the chain collapse in the first stage at T ₁ was found to persist into the third stage at the same temperature T₁ without being affected by the temperature perturbation of T ₂ during t₂. The memory effect was observed irrespective of the time period of t₂. The positive temperature perturbation (T₁<T₂) showed an acceleration of the chain-collapse process.

DOI： 10.1063/1.1825372

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.6

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2020.5

Language：Japanese  

Country：Japan  

Event date： 2020.5

Language：Japanese  

Country：Japan  

Event date： 2020.3

Language：English  

Country：Japan  

Event date： 2019.9

Language：Japanese  

Country：Japan  

Event date： 2019.6

Language：Japanese  

Country：Japan  

Event date： 2019.6

Language：Japanese  

Country：Japan  

Event date： 2018.12

Language：English  

Country：Japan  

Event date： 2018.10 - 2019.10

Language：Japanese  

Country：Japan  

Event date： 2018.6

Language：Japanese  

Venue：名古屋   Country：Japan  

Event date： 2017.10

Language：Japanese  

Venue：新潟   Country：Japan  

Event date： 2017.9 - 2018.9

Language：English  

Venue：Kyoto   Country：Japan  

Language：Japanese  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：19

Type：Academic society, research group, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：10

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：5

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.