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| 1.
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Maki, Yasuyuki ; Dobashi, Toshiaki ; Nakata, Mitsuo
概要:
application/pdf<br />Journal Article<br />The molecular weight and solvent dependences of the characteristic time of cha
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in 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.
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| 2.
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Shen, Zheyu ; Terao, Ken ; Maki, Yasuyuki ; Dobashi, Toshiaki ; Ma, Guanchui ; Yamamoto, Takao
概要:
application/pdf<br />Journal Article<br />Poly(N-isopropylacrylamide) (PNIPAM) and random copolymers of Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNIPAM-HEMA), poly(N-isopropylacrylamide-co-acrylamide)
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(PNIPAM-AAm) and poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (PNIPAM-DMAA) with various volume fractions of NIPAM g, were synthesized by radical polymerization. The phase behavior of the polymers in water was investigated by means of optical transmittance and dynamic light scattering. With decreasing g, the cloud point temperature Tcp for PNIPAM-HEMA decreased whereas Tcp for both PNIPAM-AAm and PNIPAM-DMAA increased. Increase of hydrodynamic radius around Tcp resulted from the aggregation of the globules of each polymer was observed from dynamic light scattering. The relationships between the reciprocal of Tcp of the polymer solutions and 1-g were linear for the three copolymers in the experimental range of 0.65 < g < 1. The results are discussed from the aspect of the interaction parameters of copolymer solutions.
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| 3.
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Furusawa, Kazuya ; Dobashi, Toshiaki ; Morishita, Satoshi ; Oyama, Mikio ; Hashimoto, Tadashi ; Shinyashiki, Naoki ; Yagihara, Shin ; Nagawasa, Naotsugu
概要:
application/pdf<br />Journal Article<br />Electron beam was irradiated on 10% and 20% hydroxypropylmethylcellulose (HPMC) aqueous solutions with different doses to make gel films. As increasing dose, the gel fraction of the film
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increased sharply above a critical dose and then decreased gradually after passing a maximum. The scission/cross-linking ratio and the critical dose were determined using the Charlesby-Rosiak equation as 0.52 and 9 kGy for 10% gel and 0.43 and 14 kGy for 20% gel, respectively. The gel fraction for 20% HPMC film was lower at low dose and higher at high dose than that for 10% film. The behavior of the swelling ratio of the gel film was just opposite to that of the gel fraction. The cross-linking density of the gel estimated from the Flory theory linearly increased with irradiation dose at low dose, passed a maximum around 100 and 160 kGy for 10% and 20% films, respectively, and decreased at high dose. These results suggest the competition of scission and cross-linking induced by indirect effect of irradiation. Dielectric relaxation measurement by time domain reflectometry and RF impedance/material analyzer revealed two characteristic relaxations of chain motions around 100MHz and of orientation of free water around 20GHz. From the dose dependence of the relaxation parameters determined by fitting to a combined equation of Cole-Cole type and KWW type, a coupling of motions of HPMC molecules and water molecules was strongly suggested. The critical dose for gelation was coincident with the dose for the maximum of t h and the minimum of Deh together with the minimum of t m and the maximum of Dem, where t h and Deh denote the relaxation time and the relaxation strength for free water molecular motion and t m and Dem the corresponding ones for HPMC molecular motion. The characteristic behavior was discussed in terms of the increase of affinity between HPMC and water and the constrained molecular motion in the gel network.
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| 4.
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Sato, Masumi ; Nobe, Masahiro ; Dobashi, Toshiaki ; Yamamoto, Takao ; Konno, Akira
概要:
application/pdf<br />Journal Article<br />We have found that the dialysis of curdlan dissolved in alkaline solution into aqueous solutions of metal salts yielded multifold gel structures. Aqueous sodium chloride and potassium chloride
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as well as pure water induced isotropic gels. Aqueous calcium salts induced liquid crystalline gel with refractive index gradient/amorphous gel alternative structure. Aqueous salts of trivalent aluminum and ferric cations induced a rigid liquid crystalline gel, which shrank above a threshold concentration of each salt. On the other hand, Liesegang ring-like pattern was observed with aqueous solutions of mixed salts of calcium chloride and magnesium chloride. The patterns have been classified to discuss the mechanism of forming the variety of structures.
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| 5.
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Narita, Takayuki ; Terao, Ken ; Dobashi, Toshiaki
概要:
application/pdf<br />Journal Article<br />Core-shell nanoparticles have been prepared by irradiation of gamma-ray on block copolymer micelles consisting of hydrophilic polyacrylic acid and hydrophobic polyisoprene with each 40 monomer
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units. The structure was determined by means of dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The size distribution of the core-shell nanoparticles determined by DLS and AFM was very narrow. The average diameter of the particles decreased from 48 nm for the original micelles to 26 nm by the irradiation of 30 kGy. The core size determined by SAXS combined with DLS was roughly constant of 10 nm, irrespective of irradiation dose, whereas the shell thickness of the micelles was twice as large as core size, and decreased with increasing irradiation dose.
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| 6.
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Yamamoto, Takao ; Dobashi, Toshiaki ; Suzuki, Daisuke ; Narita, Takayuki
概要:
application/pdf<br />Journal Article<br />Reentrant volume phase transition of hydrogel wall membrane of microcapsules (MC) was first observed using MC suspensions consisting of poly(L-lysine-alt-terephthalic acid) wall and aqueous
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inner and outer solutions with different pHs. To analyze the dynamics of the reentrant phase transition, we extended the theory for the swelling and the shrinking dynamics of the microcapsule gel (Langmuir 2003, 19, 4051-4054). In the theory, the microcapsule size and the force constant for the driving force which give rise to the size relaxation were chosen as the thermodynamic variables. The time course of the cross-sectional area of the microcapsules fitted well to the theoretical equations, and the time constants determined as the fitting parameters were discussed in terms of the force constant relaxation and the size relaxation.
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| 7.
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Furusawa, Kazuya ; Terao, Ken ; Nagasawa, Naotsugu ; Yoshii, Fumio ; Kubota, Kenji ; Dobashi, Toshiaki
概要:
application/pdf<br />Journal Article<br />Nanometer-sized gelatin particles have been prepared by means of gamma-ray irradiation and characterized by static and dynamic light scattering combined with circular dichroism measurements. The
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molecular weight of the nanoparticles was much larger than that of the original gelatin molecules, whereas the hydrodynamic radius was much smaller. Radius of gyration evaluated from the angular dependence of the static light scattering intensity decreased with increasing irradiation dose. Circular dichroism spectra of the gelatin nanoparticles were independent of temperature, and it is suggested that the nanoparticles consist of highly and randomly packed gelatin and their conformation is stable against the temperature change.
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| 8.
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Chang, Chih Pong ; Dobashi, Toshiaki
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application/pdf<br />Journal Article<br />Alginate complex capsules containing eucalyptus oil were prepared by the interfacial insolubilization reaction and its controlled release characteristics were examined. The capsule walls became
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substantially impermeable to eucalyptus oil by incubating the capsules at 37 oC for 20 min, when the preparation parameters were above the critical values of 1.0 w/v % sodium alginate, 2.0 w/v% calcium chloride and 20 min of the cross-linking time. The maximum oil content in the capsules was 90~92 % at this condition. The time course of the oil release from the closed capsules was measured as a function of crashing force. It was confirmed that holding the capsules between fingers could control the oil release.
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| 9.
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Sawa, Kouchi ; Kondo, Shingo ; Ooi, Kazuko ; Ichikawa, Hisashi ; Dobashi, Toshiaki
概要:
application/pdf<br />Journal Article<br />Viscoelastic (VE) and dynamic light scattering (DLS) analyses of fish (white croaker) myosin solutions were performed at myosin concentrations of 30mg/ml for VE and 0.1mg/ml for DLS at 0.6
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MKCl and pH 7.0 to clarify thermally induced gelation. The hydrodynamic radius Rh considerably decreased around 30-35oC. The shear modulus G was constant below 25oC and increased by incubating the sample at 30oC. G further increased as the temperature of the incubated sample decreased. The curves of G vs. T for different time courses showed a sharp peak around 35oC and a moderate peak around 60oC in the heating process, while a stepwise increase in G was observed around 30oC in the cooling process when the temperature was elevated to not more than 60oC. No distinct stepwise change was observed once the temperature of the sample exceeded 60oC. The absolute value of G strongly depended on the maximum elevated temperature and the incubation time at that temperature. The corresponding behavior of the viscosity h was observed for each time course. Based on these results, the mechanism of thermally induced gelation of myosin solutions is discussed in view of S-S bridge formation in the head and tail portions and unwinding/rewinding of coiled-coil a-helices in the tail portion.
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| 10.
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Dobashi, Toshiaki ; Koizumi, Jun-ichi ; Kita, Rio
概要:
application/pdf<br />Journal Article
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