Takahiro Sato

Osaka University, Suika, Ōsaka, Japan

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Publications (147)583.85 Total impact

  • Takashi Okuhara · Takahiro Sato
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    ABSTRACT: Colloidal dispersions were prepared by adding water to methanol (MeOH) solutions of a hydrophilically modified poly-(dimethylsiloxane) (HPM-PDMS) up to weight fractions of water equal to or greater than 0.6, at which the ternary solution is in the biphasic region. Static light-scattering measurements of the colloidal dispersions demonstrated that the internal concentration of the colloidal droplets was remarkably higher than that of solutions of HPM-PDMS directly dissolved in MeOH–water mixtures of the same water contents, which were studied previously. This difference in the internal structure of the colloidal droplets affects the van der Waals attraction and also the stability of the colloidal particles.
    No preview · Article · Nov 2015 · Polymer Journal
  • Rintaro Takahashi · Takahiro Sato · Ken Terao · S.-I. Yusa
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    ABSTRACT: We have investigated the self-assembly in dilute aqueous solutions of a mixture of an anionic-neutral block copolymer (AP) and a cationic-neutral block copolymer (MP) by changing the added sodium chloride (NaCl) concentration CS or electrostatic interactions among oppositely charged blocks, by direct observation, optical and electron microscopies, and small-angle X-ray scattering. The ratio of the charged to neutral block chain lengths was ca. 10, and the total copolymer concentration and the mixing ratio (the mole fraction of the MP charge unit in the total charge units) of AP and MP were fixed to be 0.005 g/cm3 and 0.6, respectively. With decreasing CS from 2 to 0 M, we have found reentrant one-phase, two-phase, one-phase transitions in the aqueous solution of the AP-MP mixture. The two-phase to one-phase transition at CS ∼ 0.5 M arises from the competition between the macroscopic phase transition and micellization, which is the first observation in dilute block copolymer solutions. Moreover, we have found a micelle morphology transition from the bilayer vesicle to the cylindrical micelle with further decreasing CS from 0.5 M to lower than 0.05 M.
    No preview · Article · Sep 2015 · Macromolecules
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    ABSTRACT: Block copolymers of N-tert-butoxycarbonyl-L-valine 4-ethynylanilide (1a) and N-tert-butoxycarbonylglycine 4-ethynylanilide (1b) with various compositions were synthesized by block copolymerization using [(nbd)Rh{C(Ph)=CPh2}(PPh3)]/PPh3 catalyst. The block copolymers exhibited intense Cotton effects in the absorption region of the conjugated polyacetylene backbone in CHCl3, THF and DMF, indicating the formation of predominantly one-handed helical structures. Amplification of g values as a function of chiral unit content was observed in the block copolymers. The relationship between g/gmax and molecular weight of the achiral block agreed with the predictions of the Ising model for a linear cooperative system, confirming the presence of chirality transfer from the chiral block to the achiral block.
    No preview · Article · Jul 2015
  • Source
    Shun Nakano · Akihito Hashidzume · Takahiro Sato
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    ABSTRACT: 3-Azido-1-propyne oligomer (oligoAP) samples, prepared by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization, were quarternized quantitatively with methyl iodide in sulfolane at 60 °C to obtain soluble oligomers. The conformation of the quarternized oligoAP in dilute DMSO-d 6 solution was examined by pulse-field-gradient spin-echo NMR based on the touched bead model.
    Full-text · Article · Jun 2015 · Beilstein Journal of Organic Chemistry
  • Tomoe Arai · Akihito Hashidzume · Takahiro Sato
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    ABSTRACT: Water-induced formation of reverse micelles from polystyrene-b-poly(N-isopropylacrylamide) (PS(x)-PN(y), where x and y were the degrees of polymerization of PS and PN blocks, respectively) in 1,2-dichloroethane (DCE) was investigated mainly by light scattering. Four PS(x)-PN(y) samples with different degrees of polymerization x and y were prepared by the reversible addition-fragmentation chain-transfer (RAFT) radical polymerization technique. While PS(x)-PN(y) was molecularly dispersed in DCE, the addition of water remarkably enhanced scattering light intensity from the DCE solutions of all the PS(x)-PN(y) samples, indicative of the formation of the reverse micelle having a water pool as the micellar core. Static light scattering (SLS) data for PS(x)-PN(y)/water/DCE ternary systems were analyzed using a model of spherical reverse micelle to estimate structural parameters, which were dependent on the hydrophilic-hydrophobic balance, i.e., y/x.
    No preview · Article · Jun 2015 · Macromolecules
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    ABSTRACT: The dehydration and self-association of a novel thermosensitive diblock copolymer consisting of poly(2-isopropyl-2-oxazoline) and poly(N-isopropylacrylamide) (PIPOZ-b-PNIPAM) upon heating were studied in water and water methanol (MeOH) mixtures by differential scanning calorimetry (DSC), turbidimetry, small-angle X-ray scattering (SAXS), and fluorescence depolarization. Although the difference of the phase-separation temperatures of the PIPOZ and PNIPAM homopolymers solutions was enhanced as the MeOH content in the mixed solvent increases, the DSC thermograms of PIPOZ-b-PNIPAM in water MeOH mixtures were not bimodal, which indicates that the dehydration of each block does not occur independently. As a result, the amphiphilicity of this copolymer is weaker in the amphiphilic condition than that of the related thermosensitive block copolymer of PIPOZ and poly(2-ethyl-2-oxazoline) (PIPOZ-b-PEOZ) examined previously, which undergoes phase separation in hot water under the same conditions. Both PIPOZ-b-PNIPAM and PIPOZ-b-PEOZ solutions undergo a temperature-induced liquid liquid phase separation, but the formation of the spherical micelle in the coexisting dilute phase is more difficult in the former solution. The colloidal stability of the coexisting concentrated phase depends on the mixed solvent composition. The colloids flocculate in conditions for which the copolymer is of intermediate amphiphilicity, as observed previously also in the PIPOZ-b-PEOZ solution, possibly due to the viscoelastic effect experienced by colloidal particles bearing on their interface chains of a more hydrophilic block.
    No preview · Article · Oct 2014 · Macromolecules
  • Ken Morishima · Takahiro Sato
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    ABSTRACT: We have investigated aqueous micellar solutions of mixtures of a surfactant (dodecylpyridinium chloride) and a hydrophobe (1-dodecanol) near the critical micelle concentration (cmc), using simultaneous static and dynamic light scattering measurements. The static light scattering intensity for the aqueous solutions was separated into fast and slow relaxation components using dynamic light scattering results. The slow relaxation component gave us the information about the large scattering component. It turned out from this component that the amount of large colloidal particles of the hydrophobe was very tiny in the solution and hardly affects the association-dissociation equilibrium of the hydrophobe-uptake micelle. The free surfactant molecule and the hydrophobe-uptake spherical micelle in the solutions belong to the fast relaxation component. We have characterized the spherical micelle and also analyzed the association-dissociation equilibrium of the hydrophobe-uptake micelle up to near the cmc, using this scattering component extracted.
    No preview · Article · Sep 2014 · Langmuir
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    ABSTRACT: The phase behavior of aqueous solutions of copolymers of fumaramide (FAM) and N-isopropylacrylamide (NIPAM) was studied by optical transmittance spectroscopy, infrared (IR) spectroscopy, and differential scanning calorimetry (DSC) to reveal the effect of the fumaramide substituents upon the phase behavior. The clouding-point and clearing-point temperatures (Tcloud and Tclear, respectively) of aqueous solutions increased with increasing mole fraction of FAM (xF), indicating that the FAM unit increases the hydrophilicity of the copolymer. IR and DSC data indicate that cooperative dehydration and rehydration occurs around Tcloud and Tclear, respectively. The cooperativity of the phase transition was lower at higher xF presumably because of a broader distribution of comonomer composition.
    No preview · Article · Aug 2014 · Kōbunshi rombun shū
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    ABSTRACT: Hydrophilically modified poly(dimethylsiloxane) (HPM-PDMS) bearing quaternized amino groups on the side chains was dissolved in mixtures of methanol (MeOH) and water with a water weight fraction w(H2O) from 0 to 1 and with 0.1m sodium acetate added. The degree of substitution and the degree of polymerization of this ionomer sample were 16 mol% and 1050, respectively, and the polymer concentrations were mostly <1%. Although the solutions were almost transparent, they were in the two-phase region at w(H2O),>= 0.5, and HPM-PDMS formed random aggregates at w(H2O)<0.5. In the two-phase region, the coexisting concentrated phases formed colloidal particles with radii of gyration ranging from 100 to 300nm just after dispersion. The colloidal particles, however, gradually coagulated, and the solutions became turbid when they were left standing for several days. The multiplet structure in the melt sample of HPM-PDMS may be responsible for the tentative dispersion of HPM-PDMS even in the two-phase region.
    No preview · Article · Feb 2014 · Polymer Journal
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    ABSTRACT: Two polystyrene (PS)-based amphiphilic diblock copolymers, PS(x)-PV(y) with x/y=3.3-7.7 and PS(x)-PA(y) with x/y = 1.2-13.7 (where PS(x)-PV(y) and PS(x)-PA(y) possess poly (ar-vinylbenzyl)trimethylammonium chloride and poly(2-acrylamido-2-methylpropanesulfonic acid) blocks, respectively, and x and y are the degrees of polymerization), were prepared by reversible addition-fragmentation chain transfer radical polymerization to investigate the formation of reverse micelles by these copolymers in less polar organic media. The PS(x)-PV(y) samples were more dispersible in halogenated solvents, for example, chloroform and 1,2-dichloroethane (DCE), than the PS(x)-PA(y) samples because of the higher solvophobicity of the PA block. 1 H NMR spectra for the PS(x)-PV(y) and PS(x)-PA(y) samples measured in CDCl 3 exhibited no signals that corresponded to the PV or PA blocks in the diblock copolymers, which indicated that the PS(x)-PV(y) and PS(x)-PA(y) samples formed reverse micelles in halogenated solvents with the PV or PA blocks in the core. The structures of the reverse micelles formed from the PS(x)-PV(y) samples in DCE were investigated in detail by static and dynamic light scattering. The light scattering data indicated that PS(x)-PV(y) formed star-like micelles at x/y>6 and non-star-like micelles at x/y<6 in DCE. The morphology of the micelles formed from PS(x)-PV(y) with x/y<6 in DCE was most likely brush-like.
    No preview · Article · Sep 2013 · Polymer Journal
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    ABSTRACT: Small-angle X-ray scattering measurements were made for nine cyclic amylose tris(n-butylcarbamate) (cATBC) samples ranging in the weight-average molar mass Mw from 1.6 × 104 to 1.1 × 105 to determine the z-average mean-square radius of gyration S2z and the particle scattering function P(q) in two good solvents, tetrahydrofuran (THF) and methanol (MeOH) at 25 °C and in a Θ solvent, 2-propanol (2PrOH) at the Θ temperature (35 °C). Static and dynamic light scattering measurements were carried out for cATBC in 2PrOH to determine Mw, the second virial coefficient A2, and the hydrodynamic radius RH. The dimensional and hydrodynamic properties are consistently explained by the current theories for wormlike ring having substantially the same model parameters obtained for linear analogues, that is, the Kuhn segment length λ–1 of THF, 2PrOH, and MeOH are 75, 20, and 11 nm, respectively. Furthermore, number of hydrogen bonds decreases with the order of THF, 2PrOH, and MeOH, as is the case with linear ATBC. These results indicate that cATBC has rigid helical backbone stabilized by intramolecular hydrogen bonds in THF and it loosens with increasing solvent polarity. Indeed, lyotropic liquid crystallinity was found for cATBC in THF. In the Θ condition, 2PrOH at 35 °C, cATBC has large positive A2 values, (1.3–1.4) × 10–4 mol g–2 cm3. It is successfully explained by the simulation results considering intermolecular topological interaction.
    No preview · Article · Jul 2013 · Macromolecules
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    ABSTRACT: Lyotropic liquid crystallinity was investigated for amylose tris(n-butylcarbamate) (ATBC), amylose tris(ethylcarabamate) (ATEC), and amylose tris(n-hexylcarbamate) (ATHC) in tetrahydrofuran (THF) and ethyl lactates (ELs) by using phase separation experiments, polarized microscopic observation, small-angle X-ray diffraction, and circular dichroism measurements. Concentrated THF solution of ATBC has selective reflection at visible light wavelength, indicating the formation of cholesteric phase. A current theory well explains the phase diagram of ATBC, ATEC, and ATHC in THF. On the other hand, ELs solution forms smectic phase and it has significantly different phase diagram, that is, the biphasic range is much wider than that in THF. In other words, highly concentrated smectic phase can be obtained from semidilute and rather low viscosity ELs solution. This is likely because amylose alkylcarbamate chains may have significant anisotropic intermolecular attractive interaction in between polymer chains in ELs or intermolecular interactions between the chain ends are much more different from those in THF.
    No preview · Article · Jul 2013 · Macromolecules
  • Akihito Hashidzume · Tomoaki Nakamura · Takahiro Sato
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    ABSTRACT: Copper-catalyzed azide-alkyne cycloaddition polymerization of 3-azido-1-propyne derivatives, i.e., 3-azido-1-propyne (Apr) and 3-azido-1-butyne (ABu), was investigated using the corresponding bromides as monomer precursors. The APr and ABu oligomers were soluble in strong acids, but insoluble in many organic solvents. IR and solid-state C-13 NMR spectra confirmed that the APr and ABu oligomers were composed of 1,2,3-triazole units. Powder X-ray diffraction patterns indicated that the APr oligomer was crystalline whereas the ABu oligomer was almost amorphous. Thermogravimetric analysis data indicated that the residual weights were as large as 54 and 46% for the APr and ABu oligomers, respectively, at 500 degrees C.
    No preview · Article · Jun 2013 · Polymer
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    ABSTRACT: The self-association behavior of a thermosensitive amphiphilic block copolymer, poly(N-isopropylacrylamide)-b-poly(N-vinyl-2-pyrrolidone) (PNIPAM-b-PNVP) in water upon heating was investigated by static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), and pulsed field gradient NMR (PFG-NMR). Combining SLS and DLS with SAXS and PFG-NMR, we conclude that above 40 degrees C, the unimer or a few arms star micelle of the copolymer coexists with large spherical particles of uniform density, which should be regarded as concentrated-phase droplets produced by a liquid liquid phase separation. The spherical particles of PNIPAM-b-PNVP samples with the PNIPAM content less than 0.32 became smaller with increasing temperature. This temperature dependence was explained in terms of the packing parameter for amphiphiles.
    No preview · Article · Jan 2013 · Macromolecules
  • Maiko Tsuda · Ken Terao · Shinichi Kitamura · Takahiro Sato
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    ABSTRACT: Six amylose-2-acetyl-3,6-bis(phenylcarbamate) (AAPC) samples ranging in weight-average molar mass M(w) from 1.8 × 10(4) g mol(-1) to 1.1 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples. Static light scattering, small-angle X-ray scattering, sedimentation equilibrium, and viscosity measurements were made for the samples in 1,4-dioxane (DIOX), 2-ethoxyethanol (2EE), and 2-butanone (MEK) all at 25°C to determine particle scattering functions, z-average radii of gyration, intrinsic viscosities, as well as M(w) . The data were analyzed in terms of the wormlike cylinder model mainly to yield the helix pitch per residue h and the Kuhn segment length λ(-1) , which corresponds to twice of the persistence length. The latter parameters (λ(-1) ) in 2EE (11 nm) and MEK (12 nm) are quite smaller than those for amylose tris(phenylcarbamate) (ATPC) in the same solvent (16 nm in 2EE and 18 nm in MEK) whereas those for AAPC (21 nm) and ATPC (22 nm) in DIOX are essentially the same as each other. This indicates that the chain stiffness of AAPC is more strongly influenced by the solvents since the number of intramolecular H-bonds of AAPC is more changeable than that for ATPC. © 2012 Wiley Periodicals, Inc. Biopolymers 97:1010-1017, 2012.
    No preview · Article · Dec 2012 · Biopolymers
  • Ken Terao · Natsuki Asano · Shinichi Kitamura · Takahiro Sato
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    ABSTRACT: Six cyclic amylose tris(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units N from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the z-average radius of gyration ?S2?z and the particle scattering function P(q). Molar mass dependencies of ?S2?z in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch h (or contour length) per residue and the Kuhn segment length ??1 (stiffness parameter, twice the persistence length). The latter parameter ??1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-q region, P(q) was also explained by the rigid ring having the same contour length Nh as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when N ≥ 24.
    No preview · Article · Nov 2012 · ACS Macro Letters
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    ABSTRACT: Eight amylose tris(ethylcarbamate) (ATEC) samples ranging in the weight-average molar mass M(w) from 1.0 × 10(4) to 1.1 × 10(6) g mol(-1) and five amylose tris(n-hexylcarbamate) (ATHC) samples of which M(w) varies from 4.9 × 10(4) to 2.2 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples having narrow dispersity indices and no branching. Small-angle angle X-ray scattering (SAXS), light scattering, viscometry, and infrared (IR) absorption measurements were carried out for their dilute solutions, that is, ATEC in tetrahydrofuran (THF), 2-methoxyethanol (2ME), methanol (MeOH), and ATHC in THF and 1-propanol (1PrOH) to determine M(w), particle scattering functions, intrinsic viscosities, and IR spectra. SAXS and viscosity measurements were also made on ATEC in d- and l-ethyl lactates. The data were analyzed in terms of the wormlike cylinder model to estimate the helix pitch (or contour length) per residue h and the Kuhn segment length λ(-1) (stiffness parameter, twice the persistence length). Both ATEC and ATHC have large λ(-1) in THF, that is, 33 and 75 nm, respectively, and smaller λ(-1) were obtained in alcohols, indicating that they have rigid helical conformation stabilized by intramolecular hydrogen bonds in THF. On the contrary, the helical structure estimated from the h value significantly depends on the alkyl side groups in a complex fashion, that is, h = 0.36 nm for ATEC, h = 0.29 nm for ATHC, and h = 0.26 nm for amylose tris(n-butylcarbamate) (ATBC). This is likely related to the bulkiness of side groups packed inside the amylosic helices. The solvent dependence of h, λ(-1), and the fraction f(hyd) of intramolecular hydrogen bonds for ATEC can be explained by a current model as is the case with ATBC [ Terao , K. ; Macromolecules 2010 , 43 , 1061 ], in which each contour point along the chain takes loose helical and rigid helical sequences independently.
    No preview · Article · Oct 2012 · The Journal of Physical Chemistry B
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    ABSTRACT: We have investigated the heat-induced self-association in water of a block copolymer (PIPOZ-b-PEOZ) comprising two thermosensitive blocks: a poly(2-isopropyl-2-oxazoline) block (degree of polymerization 71) and a poly(2-ethyl-2-oxazoline) block (degree of polymerization 38) using differential scanning calorimetry (DSC), static light scattering (SLS), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) together with visual observation on the macroscopic and microscopic scales. The dehydration temperatures of the PIPOZ and PEOZ blocks in water are 43 and 54 °C, respectively. When heated abruptly to 50 °C where PIPOZ-b-PEOZ is amphiphilic, the copolymer first forms star micelles that further aggregate to form large concentrated phase droplets, and finally the droplets coalesce into a bulk liquid phase, having a copolymer concentration as high as 0.8 g/cm 3. When heated abruptly to 70 °C, where both blocks are hydrophobic, the copolymer solution also separates into two liquid phases, consisting of phase-separated polymer-rich micrometer or submicrometer size droplets dispersed in a polymer-poor liquid phase, but the droplets do not coalesce into a liquid bulk phase. We discuss the role of the more hydrophilic PEOZ block in the macroscopic phase separation behavior. No microphase separation takes place in the concentrated phase of the aqueous PIPOZ-b-PEOZ block copolymer solution. © 2012 American Chemical Society.
    No preview · Article · Aug 2012 · Macromolecules
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    ABSTRACT: Light and small-angle X-ray scattering and viscosity measurements were made for four curdlan tris(phenylcarbamate) (CdTPC) samples having quite narrow dispersity indices (DI) and ranging in the molecular weight between 6 × 104 and 2 × 106, to determine weight-average molecular weights Mw, radii of gyration 〈S2〉〈S2〉, particle scattering functions P(q), and intrinsic viscosities [η] in tetrahydrofuran (THF) and 4-methyl-2-pentanone (MIBK). Size-exclusion chromatography equipped with light scattering and/or viscosity detectors was performed for some broad DI samples in THF also to determine 〈S2〉〈S2〉 and [η] as a function of Mw. The solution data were analyzed in terms of the wormlike-chain model to estimate the Kuhn segment length of 57 nm in THF and 17 nm in MIBK and the helix pitch per residue h of 0.39 nm in THF and 0.51 nm in MIBK. Since the former h value is almost equivalent to that for single helical curdlan and its acetate derivative in crystal, it is reasonably suggested that the local conformation of CdTPC in THF is close to the tightly wound helix stabilized by the intramolecular hydrogen bonding, which was detected from the solution IR spectra.
    No preview · Article · Aug 2012 · Polymer
  • Keiko TAMADA · Hiroki YAMAMURA · Ken TERAO · Takahiro SATO
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    ABSTRACT: The conformation of thermally denatured single-stranded DNA was studies by size exclusion chromatography equipped with a multi-angle light scattering on-line detector (SEC-MALS) and small angle X-ray scattering (SAXS). A sonicated sodium salt DNA sample from salmon testes dissolved in 0.015 M aqueous NaCl was kept at 85 degrees C for 10min, and then cooled to 10 degrees C at different ionic strengths before SEC-MALS and SAXS measurements. The results were analyzed using the wormlike chain or wormlike cylinder model to determine the contour length per nucleotide unit, the persistence length representing the polymer chain stiffness, and the chain thickness. The parameters obtained indicate that the single-stranded DNA chain is a typically flexible polyelectrolyte, of which conformation does not take the fully extended conformation but locally helical conformation.
    No preview · Article · Jul 2012 · Kōbunshi rombun shū