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Volume 26 (1998)
- Issue 4 Pages 191-
- Issue 3 Pages 137-
- Issue 2 Pages 75-
- Issue 1 Pages 7-
Volume 26, Issue 2
Displaying 1-8 of 8 articles from this issue
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Yoshiyuki EINAGA, Hiroshi FUJITA1998 Volume 26 Issue 2 Pages 75-86
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSThe correlation of concentration fluctuations in semi-dilute and concentrated polymer solutions decays with time by two mechanisms. One is the diffusion of polymer and solvent molecules due to gradients of their chemical potentials, and the other is the deformation of polymer chains due to the stress generated by disturbances of their equilibrium distributions. Thus, the dynamic structure factor S (q, t), measured by dynamic light scattering as a function of time t and the magnitude of scattering vector q, could be related to the viscoeleastic behavior of polymer solutions in the entangled region. This idea was first worked out by Brochard and also by Adam and Delsanti and recently has gained a renewed interest leading to many theoretical and experimental studies. Among the results so far reported, two typical formulations of S (q, t), one by Onuki (and also by Doi and Onuki) and the other by Wang, are of particular interest, because they make conflicting predictions. Thus, Wang's theory concludes that the stress effect on S (q, t) vanishes in systems where the polymer and solvent components have the same partial specific volumes, while Onuki's theory denies such a conclusion. Experimentally, Brown et al. support Onuki's, but Wang et al. do not yield by presenting experimental data that favor Wang's. The dispute between the two groups yet remains undecided. This review article summarizes and discusses recent contributions, both in theory and in experiment, to S (q, t) of semi-dilute and concentrated polymer solutios. The presentation includes our formulation and new experimental results by Einaga and Karube.View full abstractDownload PDF (1648K) -
Chyusaku YOSHIKAWA, Noriyasu MORI, Kiyoji NAKAMURA1998 Volume 26 Issue 2 Pages 87-94
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSNumerical simulations were performed for the flows of liquid crystalline polymers (LCPs) through abrupt contraction-expansion geometries. The constitutive equation used was a modified Doi model. The evolution equation of components of orientational order-parameter tensor was solved by using the method of characteristics and the time step optimum in the Runge-Kutta method.The streamlines for LCPs indicate the flow with a smaller entrance angle and a larger vortex at the contraction region and with a larger exit angle and a smaller vortex at the expansion region than those for the flow of Newtonian fluids. These features in the flow of LCPs are connected with the molecular orientation in the positive and negative elongational flow regions; the molecules prefer to orient in the direction parallel to the streamline in the contraction region and in the direction perpendicular to the streamline at the expansion region. In the region downstream from the expansion, while the distribution of the order parameter recovers to that in the developed flow between parallel plates, the disturbance in the director remains far downstream.View full abstractDownload PDF (1100K) -
Hiroshi NAKAMURA, Kazuyuki TACHI1998 Volume 26 Issue 2 Pages 95-98
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSFlow behavior and microstructure of suspension of core-shell type carboxylated acrylic particle have been examined by changing medium components. The suspending media used were 9/1 w/w water mixtures of various kinds of alcohols.
A peak in radial distribution curves for the suspensions became higher with hydrophobicity of the alcohol in the media as well as the relative viscosity. This suggests that the number of flocculated particles in the suspensions increases with the hydrophobicity of the alcohol in the media. Ottewill's model for interactions between polymer adsorbed layers on the particke was employed to interpret results obtained. Some amount of hydrated water in the shell layer was substituted by alcohol, consequently hydrophobicity of the shell layer increased. Since free water out of the shell layers acts as a poor solvent for the shell layer, attractive force between the particles increases and the flocculated structure develops.View full abstractDownload PDF (583K) -
Katsuya NAKAISHI1998 Volume 26 Issue 2 Pages 99-102
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSThe viscosity of a dilute suspension of sodium montmorillonite was measured as a function of salt concentration using a capillary viscometer, and the effect of salt concentration on the hydrodynamic interaction was discussed on the basis of the experimental results obtained. The hydrodynamic interaction of sodium montmorillonite under dispersed condition depends only on the diffuse double layer, and interaction between clay particles becomes also stronger as the thickness of the diffuse double layer increases. This fact shows that hydrodynamic interaction is caused by the second electroviscous effect.View full abstractDownload PDF (501K) -
Takehiro YAMAMOTO, Kiyoji NAKAMURA1998 Volume 26 Issue 2 Pages 103-108
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSThe start-up flow of viscoelastic fluids in an abrupt expansion channel is numerically analyzed. In the present analysis, a two-dimensional one to four abrupt expansion channel is used. The calculation is carried out at three Weissenberg numbers. The Leonov model is applied for a constitutive equation.
The change in the flow field which is caused by the Barus effect is observed. The flow pattern changes with time, and the corner vortex diminishes as the elastic property of the test fluid becomes strong with time. The results of the analysis by stress power predicts that the elastic energy, which has been stored in the upstream region, is released near the entrance of the expansion channel. Thus, it is considered that the Barus effect is related to the elastic energy. The Barus effect appears more strongly at higher Weissenberg number.View full abstractDownload PDF (786K) -
Masayuki SAKURAI, Kenhachi MITSUHASHI, Shigeru HINATA, Akira SHINOHARA1998 Volume 26 Issue 2 Pages 109-113
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSThe following stress-strain relation was used for the estimation of the stress-strain behavior of rubber vulcanizates: f={G-B(1-1/α)+C(α2-1)+D(α+1/a2-2)+F(α4-1)}(α-1/α2) where f is nominal stress at an extension ratio α, G corresponds to rigidity, B, C, D, and F are coefficients. The experimental stress ·strain relations of all rubber vulcanizates used in this study coincided with the above relation in the extension range almost up to the break. It was found that there existed a unique functional relation between each coefficient and the crosslink density, and the functions were determined as polynomial functions of the crosslink density. Rubber vulcanizates used were natural rubber (NR) with various contents of sulfur ranging from 0.5 to 4.5 PHR, styrene-butadiene rubber (SBR) with various concentrations of carbon black filler (SAF), and also SBR with various concentrations of oil.View full abstractDownload PDF (545K) -
Yoshio SHIRASAKI, Tetsuya TATEISHI, Atsushi KIUCHI, Shigeru KATSUTA1998 Volume 26 Issue 2 Pages 115-118
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSChanges in mechanical properties and desity of bone to deconditioning after exercise training were studied to fifty-four male rats. Mechanical tests were conducted for femur bone. The three-point bending test and stress relaxation test were performed with an Instron-type universal testing machine. Bone mineral content was measured by single photon absorptiometry at the middle site of the tibial, femur and humerus bones. The results are as follows:1) In the trained femur bone, fracture load, stiffness and deformation energy were greater than that in the control femur bone after 10weeks,19weeks and 24weeks training period; 2) Viscoelastic effect showed significant diffrences between the trained and the control femur bones;3) Density of femur and tibial bones showed significant diffrences between the trained and the control bones but also the humerus bone did diffrence tendency.View full abstractDownload PDF (505K) -
Kotaro MORITA, Xianfu WEI, Takeshi AMARI1998 Volume 26 Issue 2 Pages 119-128
Published: June 15, 1998
Released on J-STAGE: November 20, 2012
JOURNAL FREE ACCESSThe flocculated structure and flow properties of suspensions of brilliant carmine 6B (C6B) in polybutadiene were investigated. In this study, we have used simple suspensions of C6B in polybutadiene having different viscosity. Stress overshoot phenomenon after various rest periods and double-step shearing test were examined for the suspensions. In the double-step shearing test, a transient stress overshoot was observed in the suspension of C6B in lower viscosity disperse medium, when the shearing was switched suddenly from higher to lower. This peculiar phenomenon was discussed in comparison with the other kinds of suspensions and was explained from the view point of the alteration of dispersing state and formation of flocculated network structure of C6B.View full abstractDownload PDF (1306K)
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