Mitsuo Nakata

Upper and lower critical solution temperatures in poly (ethylene glycol) solutions

Upper and lower critical solution temperatures have been determined for solutions of poly(ethylene glycol) in t-butyl acetate and water over the molecular weight range of Mη = 2.18 × 103 to ∼1020 × 103. The phase diagram for solutions of poly(ethylene glycol) (Mη = 719 × 103) in t-butyl acetate was expressed as the ‘hour glass’ type, while the phase diagram for solution of poly(ethylene glycol) (Mη = 2.18 × 103 to ∼2.29 × 103) in water was expressed as the ‘closed loop’ type. The value of the pressure dependence of the lower critical solution temperature (dTdP)c in the poly(ethylene glycol) (Mη = 1020 × 103)/water system over the pressure range of 0 to ∼50 atm was negligibly small and positive.

Coexistence curve of polystyrene in methylcyclohexane. I. Range of simple scaling and critical exponents

We have measured coexistence curves for the system polystyrene–methylcyclohexane with varying molecular weight from Mw=1.02×104 to 71.9×104. In the temperature range e=(Tc−T)/Tc≳0.03, a deviation from simple scaling was observed for systems with Mw=10.9∼71.9×104. The effect of correction terms on simple scaling was negligibly small for systems with Mw=1.02∼4.64×104. This finding is compatible with molecular weight dependence of a critical value of e for the validity of the Landau theory. In the appropriate temperature range, where a contribution from the correction terms is negligible, an analysis by simple scaling gives the exponent β=0.332±0.001 independent of molecular weight. The critical exponent for the diameter is also independent of molecular weight and determined as 0.858±0.005, which is consistent with results of recent specific heat measurements.

Atomic force microscopic studies on the structure of bovine femoral cortical bone at the collagen fibril-mineral level.

The structure of cortical bone at the collagen-mineral level was investigated by means of atomic force microscopy. Surfaces of the specimens treated with collagenase and ethylenediaminetetraacetic acid (EDTA) were examined. Images of blob-like objects observed in intact specimen became clearly outlined after collagenase treatment; the sizes of the blob decreased, suggesting that each blob had been fragmented by the collagenase treatment. Following EDTA treatment of an intact specimen, an image of thread-like objects appeared; the thread was partly constructed by trains of blobs and the other parts of the threads had a periodic pattern along its longer axis. The period was almost equal to the collagen D-period of the Hodge–Petruska model, indicating that the threads are collagen fibrils and that the blobs are related to the mineral phase in bone. It was concluded that minerals were deposited on and along collagen fibrils. A decorated collagen fibril model for the spatial relationship between mineral and collagen fibril was proposed. According to our model, the mineral inside the collagen fibril is about one forth of the extrafibrillar mineral.

Characterization of curdlan in aqueous sodium hydroxide

Curdlan ((1 → 3)-β-D-glucan) was found to be fractionated through liquid—liquid phase equilibrium with the mixture dimethyl sulfoxide + lithium chloride as a solvent and acetone as a precipitant. Light scattering and viscosity measurements were made on solutions of fractionated samples in 0.3 M NaOH in the range of the molecular weight Mw, from 5.3 × 104 to 2.0 × 106. The observed intrinsic viscosity [η] was analysed by the Yamakawa—Fujii—Yoshizaki theory of a wormlike chain, and the persistence length, molecular weight per unit contour length and molecular diameter were determined roughly as 6.8 nm, 890 g nm−1 and 1.1 nm, respectively. These molecular parameters represented the molecular weight dependence of [η] and the mean-square radius of gyration 〈s2〉z, reasonably indicating an effect of the excluded volume at large Mw. Detailed behaviour of curdlan in 0.3 M NaOH could not be revealed on account of a large uncertainty caused by microgel aggregates in the light scattering measurements.

Coexistence curve for polystyrene–cyclohexane near the critical point

The coexistence curves for the system polystyrene–cyclohexane have been determined with a specially designed differential refractometer, which determines concentrations of the two coexisting phases with a precision of ± 0.01%. The plots of the coexistence curve data represented by log(X+−Xc) and log(Xc−X−) versus the reduced temperature e = (Tc−T)/Tc yield largely curved lines. The shape of the coexistence curve very near the critical point, however, is asymptotically symmetric. The coexistence curve obtained with an over‐all concentration at the critical concentration is represented by the relation X+−X− = Beβ with β=0.348 and B=0.97 in the temperature region of Tc −T<2.0 °C. The critical point exponent β and the coefficient B vary only slightly depending on the over‐all concentration. Although the data give a curved diameter, a precision of the present experiment is not sufficient to determine the asymptotic behavior of the diameter.

Coexistence curve of polystyrene in methylcyclohexane. II. Comparison of coexistence curves observed and calculated from classical free energy

Comparison of coexistence curves observed and calculated from the classical free energy was made for the systems polystyrene–methylcyclohexane and polystyrene–cyclohexane. Classical free energy was determined from the molecular weight dependence of the critical point. At low molecular weight, the numerically calculated coexistence curve was well represented by the leading term with the exponent β=1/2. The shape of the calculated coexistence curve is very different from the observed one because of the comparable values of the coefficient and different values of the exponent β observed and calculated. At high molecular weight, the entire shape of the observed coexistence curve is fairly well described by the calculated one. This fair description was caused by the large value of the calculated coefficient compared with the observed one and the narrow range of simple scaling. The numerically calculated coexistence curve was found to deviate from the leading term with β=1/2 at high molecular weight. Both in di...

Pressure dependence of upper critical solution temperatures in the polystyrene - cyclohexane system

Abstract The pressure dependence of the upper critical solution temperature ( d T d p ) c in the polystyrene-cyclohexane system has been measured over the pressure range of 1 to 50 atm. The value of ( d T d p ) c determined over the molecular weight ( M w ) range of 3.7 × 10 4 to ∼145 × 10 4 greatly depends on the molecular weight of polystyrene. The value of ( d T d p ) c for a polystyrene solution of low molecular weight ( M w = 3.7 × 10 4 ) is positive (3.14 × 10 −3 degree atm −1 ), while the values are negative (−0.52 × 10 −3 ∼−5.64 × 10 −3 degree atm − ) for solutions of polystyrene over the high molecular weight range of 11 × 10 4 to ∼145 × 10 4 . The Patterson-Delmas theory of the corresponding state and the newer Flory theory have been used to explain this behaviour.

Coexistence curve of polystyrene in methylcyclohexane. III: Asymptotic behavior of ternary system near the plait point

Coexistence curve measurements were made on the systems of polystyrene (PS) in methylcyclohexane (MC) by using the refractive index method. The entire shape of the coexistence curve of the ternary system PS I(Mw=1.72×104)–PS II(Mw=7.19×105)–MC with ξ2=0.1704 is very different from those of the binary systems PS(I)–MC and PS(II)–MC, where ξ2 denotes a volume fraction of PS(II) to total polystyrene. The asymptotic shape of the ternary coexistence curve near the critical point was found to be characterized by the exponent βt=0.384±0.004, which is close to the fully renormalized critical exponent. The direction of tie lines near the critical point was found to be parallel to each other from the calculation with the classical empirical equation of the Gibbs free energy.

Phase separation of poly(ethylene glycol)-water-salt systems

Abstract Phase separation temperatures, each corresponding to lower critical solution temperature (LCST) for solutions of poly(ethylene glycol) (PEG) in water-sodium chloride (NaCl) and in water-propionic acid-sodium salt (Pro-Na), have been determined for PEG with molecular weights of Mη = 2.18 × 103, 8 × 103 and 719 × 103 over concentration ranges from 0–1.09 M (mol/1000 g solvent) NaCl and 1.02 M Pro-Na. The phase separation temperature decreases with an increase of salt concentration and depends on polymer molecular weight. The thermal pressure coefficient, thermal expansion coefficient, and density have been determined from 20° to approximately 60°C for ethylene glycol-water solutions over the entire concentration range and also for aqueous salt solutions over the concentration ranges from 0–1.7 M NaCl and 0–0.5 MPro-Na. The excess thermal pressure coefficient, γEV, excess thermal expansion coefficient, αE, and excess of temperature dependence of γV, [ ( ∂ γV ∂T ) E ϱ ], for the EG-water system are all positive, while the excess volume of mixing VE is negative. The thermal pressure coefficient and thermal expansion coefficient for aqueous salt solutions water-Pro-Na and water-NaCl increase with an increase of salt concentration. The behaviour of the two polymer-salt-water solutions is discussed in terms of a thermodynamic equation of state, and a shortcoming of the usual formulation of the corresponding states theory of polymer solutions is pointed out.

Cloud-point curves of the polystyrene-cyclohexane system near the critical point

Abstract Cloud-point curves for solutions of five polystyrene samples, including three well-fractionated polystyrenes, in cyclohexane have been examined near their critical points. Even for a solution of polystyrene characterized by M w M n , the critical point determined by the phase-volume method is generally situated on the right hand branch of the cloud-point curve. The precipitation threshold concentration is appreciably lower than the critical concentration, while the threshold temperature slightly deviates from the critical temperature. The agreement of the precipitation threshold point with the critical point has been found for a solution of polystyrene characterized by Mw=20×104 and M w M n in cyclohexane. The η(φ) function derived from critical miscibility data is expressed by χ(φ) = 0.2798+ 67.50 T +0.3070φ+0.2589φ 2 , which yields θ of 33.2°C and ψ1 of 0.22.