Nihon Reoroji Gakkaishi
Online ISSN : 2186-4586
Print ISSN : 0387-1533
ISSN-L : 0387-1533
Volume 43, Issue 3_4
Displaying 1-10 of 10 articles from this issue
FOREWORD
ORIGINAL ARTICLES
  • Takehiro Yamamoto
    2015 Volume 43 Issue 3_4 Pages 53-62
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    Pressure-driven flows of a phototactic microalgae suspension in a transparent circular channel illuminated from its outer side were numerically analyzed. Microalgae were modeled by active phototactic particles and the volume-fraction dependence of the suspension viscosity was expressed by the Krieger-Dougherty model. The light intensity distribution in the tube was computed from the algal density distribution based on the Lambert-Beer law. The phototactic behavior of the microalgae was described using a phototaxis function, which controls both the speed and the direction of the algae, and the algal number density distribution in the tube was calculated. The number density distribution changed with the illumination intensity according to their phototactic behavior and remarkably affected the velocity profile. Non-uniformity in apparent viscosity due to the algal distribution produced an anomalous velocity profile, in which the viscous dissipation decreased around a position where the algal density was high, resulting in a high apparent viscosity. The average velocity with a constant pressure gradient increased or decreased according to the algal distribution. The average velocity tends to increase as the position of high-algal-number-density region moves to the center side because the viscosity distribution approaches to a profile effective to suppress the increase in the total amount of the viscous dissipation.
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  • Keiko Takeda, Sathish Kumar Sukumaran, Masataka Sugimoto, Kiyohito Koy ...
    2015 Volume 43 Issue 3_4 Pages 63-39
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    It has been reported that the stretch/orientation-induced reduction of friction (SORF) has the significant effect on polymer dynamics under fast elongational flows. Although the construction of SORF suggests some effects of the flow field, the earlier studies have made exclusively for uniaxial elongational flows. In this study, for the first time we examined the effect of SORF under equi-biaxial elongation by means of the primitive chain network simulation. As reported for uniaxial elongation, the simulation fairly captured the literature data for transient biaxial elongational viscosity for a polystyrene melt. On the pretext of the reproducibility, the simulation was performed up to large strains at which the viscosity exhibits steady state. The results showed that the effect of SORF is essentially insensitive to the difference of the flow field. As a consequence, the strain hardening behavior is similar to each other for uniaxial and biaxial deformations given that the strain rate is common with respect to the Rouse relaxation time.
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  • Kenji Ohmura, Tadayasu Minami, Masaaki Yanagi, Naoya Mori, Takeshi Nak ...
    2015 Volume 43 Issue 3_4 Pages 71-75
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    Transitional rheological behavior of foams due to the corruption of bubbles is important in industrial applications such as cosmetics. In this study, we characterized transitional behaviors of facial wash foams using dynamic viscoelastic measurements. We measured time development of the storage modulus and analyzed the obtained responses with respect to the multi-mode exponential decaying function. On the relaxation modulus and time, we examined the effects of the frequency and the strain amplitude of the prove strain wave. It was found that the strain amplitude and frequency affect the modulus reflecting the non-linear mechanical response of the liquid membrane and the shape relaxation of bubbles, whereas the relaxation time is insensitive to the parameters of the prove wave. We further investigated the correlations between the obtained relaxation parameters and some scores obtained in sensory assessments.
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  • Madoka Uozumi, Tadashi Matsushita, Naoki Sakamoto, Terumasa Yamazaki, ...
    2015 Volume 43 Issue 3_4 Pages 77-83
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    Simultaneous measurements of small-angle X-ray scattering with stress-strain tests were conducted to reveal changes in microphase-separated structures being correlated with changes in the mechanical properties upon the uniaxial stretching of an elastomeric block copolymer film containing glassy spherical microdomains embedded in the rubbery matrix. For this purpose, high brilliant synchrotron X-ray source was utilized at SPring-8, Japan, and cycled stretching-and-reversing process was conducted three times. While the tensile modulus decreased to be less than the half for the second cycle of the stretching, affine deformation for the changes in the microphase-separated structures was confirmed not only for the second but also for the third cycles. The Mullins effect (stress-induced softening) may be attributed to stress-induced disentangling of the soft-segment chains between two adjacent glassy spherical microdomains (as physical crosslinking points). It was found that the number density of the active network chain (νe ) is more than 22-times higher than that of the soft-segment chains between two adjacent glassy spherical microdomains (νe°) in the virgin sample. Such a big number of the active network chain suggests that the soft-segment chains between two adjacent glassy spherical microdomains are heavily entangled. Furthermore, it was found that the ratio νee° is still around 10 for the second and third stretching cycles, suggesting that appreciable number of entanglements can be relaxed while comparable number of entanglements cannot be. The latter is so referred to as “trapped entanglement due to crosslinking”.
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  • Koji Masuda, Hiroshi Suzuki, Yoshiyuki Komoda, Ruri Hidema
    2015 Volume 43 Issue 3_4 Pages 85-92
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    Two-dimensional numerical computations of unsteady flow of a suspension between two coaxial cylinders are performed. We investigate the dispersion characteristics based on a novel thixotropy model. The diameter of particles, solid volume fraction, and viscosity of dispersing media are set to 2.5 µm, 0.15, and 195 Pa·s, respectively. The shear rate is suddenly changed from 0.1 s-1 to 1 s-1. For model validation, the numerical results are compared with previously reported experimental results. The mean number of particles in a cluster increases slightly shortly after the shear rate change, reaches a maximum, and subsequently decreases, finally attaining a steady state at 40 s after the shear rate change. Our model better expresses the time variation of the dispersion characteristics than the previous model. After the validation, the effect of bonding energy on the time-variation characteristics is investigated. The bonding energy is varied as 2.7 × 10-13, 2.7 × 10-12, and 2.7×10-11 J. We observe that the asymptotic values of the mean number of particles in a cluster depend on the bonding energy, but this relationship is not linear. From our results, we posit the existence of a certain critical bonding energy with regard to the dispersion characteristics.
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  • Yuuki Kosugi, Yoshiaki Matsuoka, Kenji Urayama
    2015 Volume 43 Issue 3_4 Pages 93-98
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    The yielding behavior of the melts of poly(n-butyl)acrylate rubber-particles with various cross-link densities in feed (cx) is investigated by the creep and recovery tests, and the large amplitude oscillation (LAOS) measurements. The measurements reveal the presence of a yield stress for the onset of plastic flow. The equilibrium shear modulus (G0), which is measured at the small stresses below the yield stress, increases with an increase in cx as G0 ~ cx0.5. The yield strain (γc ≈ 2 × 10-2) is almost independent of cx and temperature. The cx-insensitive γc is qualitatively similar to the earlier results for the highly dense suspensions of micro-hydrogels.
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  • Ryota Noso, Tomoya Kimura, Keisuke Sakamoto, Masako Sugihara-Seki, Jun ...
    2015 Volume 43 Issue 3_4 Pages 99-104
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    In blood flow through microvessels, platelets are known to have enhanced concentrations near the vessel wall, which is the so-called “near-wall excess”. In the present study, the spatial distribution of platelet-sized polystyrene particles in red cell suspension flowing through microchannels with a square cross-section of 50 μm width was measured by a confocal laser scanning microscope. The measurements were performed at the flow rate of 1.0 μL/min for various particle diameters (d = 1.0 - 4.8 μm) and various volume fractions of red cells (hematocrit; Hct = 0 - 40 %). In the absence of red cells, the particles were uniformly distributed in the channel cross-section. For all cases studied, their distributions were also uniform at the inlet of the channel. At downstream cross-sections, high concentrations of particles near the channel wall were obtained in the presence of red cells. This tendency was enhanced for higher hematocrits and larger particles. The cross-sectional distribution of the particles revealed enhanced particle probability near the channel corners rather than near the center of the channel faces, suggesting that the particles are focused mainly close to the corners due to the square cross-section of the channel.
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NOTE
  • Hiroshi Watanabe, Yumi Matsumiya, Tadashi Inoue
    2015 Volume 43 Issue 3_4 Pages 105-112
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    For flexible polymers, the deviatoric parts of the stress and optical anisotropy tensors, with the latter reflecting the orientational anisotropy of the monomeric segments, are proportional to each other. This proportionality, known as the stress-optical rule (SOR), is valid not only in the linear viscoelastic regime but also in the moderately nonlinear regime, given that the chain is not highly stretched and is free from the finite extensible nonlinear elasticity (FENE) effect. On start-up of flow in such a moderately nonlinear regime, the chain exhibits an overshoot of the shear stress and thus of the shear component of the segmental orientational anisotropy. Nevertheless, it was not clearly understood whether this overshoot is associated with an overshoot of chain stretch. This study revisited SOR to conduct a simple analysis for this problem. It turned out that the orientational anisotropy of subchains overshoots but the subchain stretch (identical to the chain stretch) does not when the shear stress overshoots in the moderately nonlinear regime.
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ORIGINAL ARTICLES
  • Yuji Hirose
    2015 Volume 43 Issue 3_4 Pages 113-117
    Published: September 15, 2015
    Released on J-STAGE: September 05, 2015
    JOURNAL FREE ACCESS
    We measured electrorheological (ER) properties of suspensions of titanium dioxide/polymer composite particles using electrodes with regularly arranged fine projections. For a 10 wt% suspension, particles assembled between projections of electrodes and the yield stress became higher than the case of flat electrodes. On the other hand, the ER effect of a suspension with 30 wt% particles between pattern electrodes became weaker than between flat electrodes. From the observation of column structures of particles in a dilute (5 wt%) suspension between pattern electrodes, particles assembling between mountain sections of projections and thick columns were created. In the case of a dense (30 wt%) suspension, the space between flat and pattern electrodes was jammed with particles but several cracks were observed between valley sections on pattern electrodes. It is supposed that this difference is caused by the competition between the thick columns of mountain sections and low particle concentration regions between valley sections of pattern electrodes.
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