Flow behavior was examined for a 1.0 wt % aqueous solution of hydrophobically modified ethoxylated urethane (HEUR; M w = 4.6 × 10 4 ). In the linear viscoelastic regime, the solution exhibited single-Maxwellian behavior attributable to thermal reorganization of the transient network composed of strings of HEUR flower micelles. Under shear flow at intermediate shear rates γ̇just above the equilibrium relaxation frequency 1/τ, the solution exhibited thickening characterized by monotonic increase of the viscosity growth function η + (t;γ) with time t above the linear η + (t) and by the steady-state viscosity η(γ) larger than the zero-shear viscosity η 0 . However, at those γ, the first normal stress coefficient growth function Ψ 1 + (t;γ) and its steady-state value Ψ 1 (γ) remained very close to the linear Ψ 1 + (t) and Ψ 1,0 and exhibited no nonlinearity. In addition, the relaxation times of the viscosity and normal stress coefficient decay functions η − (t;γ) and Ψ 1 − (t;γ) measured after cessation of steady flow agreed with those in the linear regime. All these results suggested that the network strands were just moderately stretched to show no significant finite extensible nonlinear elasticity (FENE) effect and that the number density ν of the network strands was negligibly affected by the shear at γ̇just above 1/τ. A simple transient Gaussian network model incorporating neither the FENE effect nor the increase of ν suggested that the thickening of η + (t;γ) and η(γ) and the lack of nonlinearity for Ψ 1 + (t;γ) and Ψ 1 (γ) could result from reassociation of the HEUR strands being in balance with the dissociation but anisotropically enhanced in the shear gradient direction. In contrast, at γ̇≫ 1/τ, η + (t;γ) exhibited overshoot above the linear η + (t) and then approached η(γ) < η 0 , whereas Ψ 1 + (t;γ) stayed below the linear Ψ 1 + (t) and approached Ψ 1 (γ) ≪ Ψ 1,0 after exhibiting a peak. The relaxation of η − (t;γ) and Ψ 1 − (t;γ) after cessation of flow was considerably faster than that in the linear regime. These nonlinear thinning features at γ̇≫ 1/τ were attributable to the flow-induced disruption of the HEUR network (and decrease of ν).

We consider concentration dependence of rheological properties of associative telechelic polymer solutions. Experimental results for model telechelic polymer solutions show rather strong concentration dependence of rheological properties. For solutions with relatively high concentrations, linear viscoelasticity deviates from the single Maxwell behavior. The concentration dependence of characteristic relaxation time and moduli is different in high and low concentration cases. These results suggest that there are two different concentration regimes. We expect that densely connected (well percolated) networks are formed in high-concentration solutions, whereas sparsely connected (weakly percolated) networks are formed in low-concentration solutions. We propose single chain type transient network models to explain experimental results. Our models incorporate the spatial correlation effect of micellar cores and average number of elastically active chains per micellar core (the network functionality). Our models can reproduce non-single Maxwellian relaxation and nonlinear rheological behavior such as the shear thickening and thinning. They are qualitatively consistent with experimental results. In our models, the linear rheological behavior is mainly attributable to the difference of network structures (functionalities). The nonlinear rheological behavior is attributable to the nonlinear flow rate dependence of the spatial correlation of micellar core positions.

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The formation of solid solutions of microwave dielectric compounds having compositions in the vicinity of Ba3.75-R 9.5Ti18O54 and/or BaO·R 2O3·4TiO2 (R=rare earth) has been investigated. 3BaO·2R 2O3·9TiO2 (Ba6 R 8Ti18O54) solid solutions with the ideal formulae of Ba6-3x R 8+2x Ti18O54 (0.0≤x≤1.0) have been derived on the tie line with the ratio Ti:O=1:3 between perovskite and R 2Ti3O9 based on the new tungsten bronze-type crystal structure with 2×2 perovskitelike unit cells. The type of solid solutions is substitutional with following the relation 3Ba2+\rightleftarrows2R 3++\Box. Lattice parameters as a function of composition have been determined by the WPPD (whole-powder-pattern decomposition) method.17) The formation range is located at 0.3≤x≤0.7 compositions in the case of R=Sm and 0.0≤x≤0.7 in R=Nd. In the latter case, two kinds of substitutions of the solid solutions are considered.

For aqueous solutions of a representative telechelic polymer, hydrophobically modified ethoxylated urethane (HEUR), a recent transient network model suggested that sparse and dense HEUR networks are formed at low and high HEUR concentrations c thereby exhibiting different rheological features [Uneyama, T.; Suzuki, S.; Watanabe, H. Phys. Rev. E 2012, 86, 031802]. In this study, we examined those differences for nonlinear rheological behavior of HEUR solutions (with M HEUR = 4.6 × 104 and c = 1–10 wt %) under steady shear at 25 °C to test the model. For rather dilute solutions (c ≤ 3 wt %), the steady state viscosity η exhibited crossover from the linear (zero-shear) behavior to thickening and further to thinning with increasing the shear rate γ̇, whereas the first normal stress coefficient Ψ1 remained in the linear regime up to intermediate γ̇ (where η exhibited the thickening) and then decreased with γ̇ in the thinning regime of η. In contrast, for concentrated solutions (c ≥ 4 wt %), η exhibited no thickening and a direct linear-to-thinning crossover was observed for both η and Ψ1. The critical HEUR concentration for the disappearance of the thickening of η, c* ≅ 4 wt %, was in agreement with that noted for the linear viscoelastic data, suggesting that the HEUR network structure changed from the sparse state to the dense state at c*, as considered in the above transient network model: At low c < c*, linear sequences of HEUR chains (superbridges) connected at the HEUR micellar cores would have served as effective strands to form the sparse network. Those superbridge strands dissociate and reassociate under steady shear, and the orientation of the reassociated strands should be quite sensitive to anisotropy of the spatial distribution of the cores (intra-strand dissociation sites) so that the thickening of η at intermediate γ̇ is accompanied by linear Ψ1, as deduced from the model. In contrast, at large c > c*, the dense network mainly sustained by individual HEUR chains would have been formed. For this case, the anisotropy of core distribution should less significantly affect the orientation of the created strands, which possibly erased the thickening of η at intermediate γ̇, as suggested by the model. Thus, the changes of the nonlinear behavior with c observed in this study were in harmony with the expectation from the model, lending qualitative support to the structures and dynamics of the networks considered in the model. In addition, the flow visualization using tracer particles confirmed that the flow was uniform up to the onset of thinning of η and Ψ1 (which is again in harmony with the model) and that the flow was destabilized to form shear bands in the thinning regime as similar to the behavior of a wide variety of softmatters.

Experimental Bayesian optimization for Li ion conductivity in NASICON-type LiZr2(PO4)3.

Lithium intercalation properties of octatitanate synthesized through exfoliation/reassembly process, denoted reassembled-octatitanate, were examined for the first time and compared with those of octatitanate prepared without the exfoliation/reassembly process. Reassembled-octatitanate was prepared by the exfoliation of tetrabutylammonium-intercalated tetratitanate compound and the reassembly of the obtained nanosheets. The electrochemical activity was maintained in the reassembled-octatitanate. The overvoltage of reassembled-octatitanate was smaller than that of a conventional octatitanate. The reversible capacity and energy efficiency of reassembled-octatitanate were 170 (mA h)/g and 91%, respectively, larger than those of a conventional octatitanate. The exfoliation/reassembly process was found to be effective in improving the electrode performance.

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