• Journal of the Korean Applied Science and Technology
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• v.32 no.3
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• pp.386-393
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• 2015

The rheological properties of complex materials such as colloid dispersion show complicated non-Newtonian flow phenomena when they are subjected to shear flow. These flow properties are controlled by the characteristics of flow units and the interactions among the flow segments. The rheological parameters of relaxation time $({\beta}_2)_0$, structure factor $C_2$ and shear modulus $X_2/{\alpha}_2$ for various thixotropic flow curves was obtained by applying thixotropic equation to flow curves. The variations of rheological parameters are directly related to non-Newtonian flows, viscosities and activation energies of flow segments.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.293-303
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• 1971

The theological properties of aqueous suspensions of Black Hills bentonite were measured by using a Couette-type viscometer. Three kinds of flow units in aqueous bentonite suspension were postulated. Each has a different average relaxation time, one Newtonian. One of the non-Newtonian types is thixotropic, and the other is non-thixotropic. The thixotropic non-Newtonian unit is transformed to a Newtonian unit by shear stress. If the stress is relieved, the transformed unit returns to its original state. Two flow equations were derived by introducing chemical kinetics consideration for such a transition into the generalized theory of viscous flow. One equation describes the "upcurve," a diagram of rate of sheat versus shear stress, obtained by increasing the rate of shear, and the other relates to the "downcurve" obtained by decreasing the shear rate. The equations satisfactorilly describe the experimental thixotropic hysteresis of bentonite suspensions. The equations also were successfully applied to the flow curves of the suspensions containing various amounts of monovalent electrolyte (KCI).

• Bulletin of the Korean Chemical Society
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• v.7 no.4
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• pp.257-262
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• 1986

Thixotropy is a time-dependent shear-thinning phenomenon. We derived a new thixotropic formula which is based on the generalized viscosity formula of Ree and Eyring, $f={\Sigma}\frac{X_i}{{\alpha}_i}sinh^{-1}$ () (Refer to the text concerning the notation.) The following is postulated: (1) thixotropy occurs when small flow units attached to a large flow unit separate from the latter under stress (2) elastic energy(${\omega}$) is stored on the large flow unit during the flow process, and (3) the stored energy contributes to decrease the activation energy for flow. A new thixotropic formula was derived by using these postulations, $f={\frac}{X_0{\beta}_0}{\alpha_0}{\dot{s}}+{\frac}{X_1{\beta}_1}{{\alpha}_1}{\dot{s}}+{\frac}{X_2}{{\alpha_x}}sinh^{-1}$[$({\beta}_0)_2$ exp $(-C_2{\dot{s}}^2/RT){\cdot}{\dot{s}}$] f is the shear stress, and s is the rate of shear. In case of concentrated solutions where the Newtonian flow units have little contribution to the viscosity of the system, the above equation becomes, $f=\frac{X_2}{\alpha_2}sinh^{-1}$[$({\beta}_0)_2$ exp $(-C_2{\dot{s}}^2/RT){\cdot}{\dot{s}}$]. In order to confirm these formulas, we applied to TiO2(anatase and rutile)-water, printing ink and mayonnaise systems. Good agreements between the experiment and theory were observed.

• Journal of the Korean Chemical Society
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• v.50 no.6
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• pp.447-453
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• 2006

of synthetic conditions and water content on rheological properties of polyacrylamide hydrogels were studied. The non-Newtonian flow curves of polyacrylamide hydrogels were obtained by using a cone-plate rheometer. The rheological parameters were obtained by applying non-Newtonian equation to the flow curves for polyacrylamide hydrogels. The polyacrylamide hydrogels are shear thinning under increasing shear rate modes which result in thixotropic behavior. These flow properties are controlled by the characteristics of flow units and the interaction among the flow segments.

• Elastomers and Composites
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• v.44 no.3
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• pp.323-328
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• 2009

The rheological properties of complex materials such as polymer melts show complicated non-Newtonian flow phenomena when they are subjected to shear flow. These flow properties are controlled by the characteristics of flow units and the interactions among the flow segments. The non-Newtonian flow curves of poly(vinyl alcohol) hydrogel were obtained in various concentrations and temperatures by using a cone-plate rheometer. By applying non-Newtonian flow equation to the flow curves for PVA hydrogel samples, the rheological parameters were obtained. The PVA hydrogel samples are shear thinning under increasing shear rate modes which result in thixotropic behavior.

• Korean Journal of Food Science and Technology
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• v.12 no.1
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• pp.18-23
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• 1980

Rheological behaviors of red pepper paste acre investigated with rotational viscometer at $25{\sim}55^{\circ}C$ and the following results were obtained. 1. At shear rate of $0.323{\sim}1.653\;sec^{-1}$, red pepper paste was found to be a thixotropic food product which showed pseudoplastic proper ties and also exhibited a yield stress and time dependent characteristics. 2. At a shear rate of 0.978 $sec^{-1}$, flow behavior index, consistency index and yield stress were 0.597, 192.3 dyne $sec^s/cm^{2}$, and 91 dyne/$cm^{2}$ respectively. 3. Variation of consistency of red pepper paste with time was found to be decayed by a second order kinetic equation and thereafter nearly time independent. 4. Variation of consistency of red pepper paste with temperature was found to follow Andrade's equation and the activation energy as calculated on the basis of this equation was $1.03\;kcal/g{\cdot}mole$.

• Korean Journal of Food Science and Technology
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• v.16 no.4
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• pp.451-456
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• 1984

Rheological properties of gelatinized rice starch solutions were investigated with Brookfield rotational viscometer. The 8% starch solution showed thixotropic behavior with yield stress. The alkali gelatinized starch was more thixotropic than the thermal gelatinized one. The time dependent characteristics of starch solutions followed Tiu's model. The value of rate constant $(a_1)$ in Tiu's model increased linearly with shear rate, and was exponentially dependent on concentration and temperature. Temperature dependency of rate constant and apparent viscosity followed Arrhenius type equation and the activation energy were about 14.3 and 6.8 Kcal/g mole, respectively. The $a_1-value$ was found to be useful to evaluate changes in structaral decay on the shearing time of gelatinized rice starch solutions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.234-237
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• 2008

It was reported that the semi-solid forming process has many advantages over the conventional forming process, such as a long die life, good mechanical properties and energy savings. It is very important, however, to control liquid segregation to gain mechanical property improvement of materials. During forming process, Rheology material has complex characteristics, thixotropic behavior. Also, difference of velocity between solid and liquid in the semi-solid state material makes a liquid segregation and specific stress variation. Therefore, it is difficult for a numerical simulation of the rheology Process to be Performed. General Plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. The behavior and stress of solid particle in the rheology material during forging process is affected by viscosity, temperature and solid fraction. In this study, compression experiments of aluminum alloy were performed under each other tool shape. In addition, the dynamics behavior compare with Okano equation to Power law model which is viscosity equation.

• Elastomers and Composites
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• v.44 no.4
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• pp.423-428
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• 2009

The non-Newtonian flow curves of polyurethane melts were obtained by using a Physica cone-plate rheometer at various temperatures. The rheological parameters were obtained by applying non-Newtonian flow equation to the flow curves for polyurethane samples. When the polyurethane samples are under increasing-decreasing shear rate modes, the hysteresis loop and thixotropic behavior were shown. Polyurethane melts behave as strong gels when they are subjected to shear flow, but when the applied stress surpasses the yield stress, they exhibit non-linear viscoelasticity. Upon decreasing shear rate, its shear stress remains smaller than the values measured in the increasing shear rate mode, because of broken of its structure.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.262-268
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• 1996

Flow properties of all suspensions are controlled by their flow units. The factors effecting on the flow units are the characteristics of the particle itself (surface properties, particle sizes, particle shapes and etc.), the electrostatic interactions among the particles and the influences of the medium in the suspensions. Here, we studied the transition between the flow units with shear rate which can be added to the above factors. For the concentrated starch-water suspensions, by using the Couette type rotational viscometer, we confirmed that at low shear rate, dilatancy is appeared, but it is transformed to thixotropy with increasing shear rate. In order to explain this fact, we derived the following flow equation, representing the transition from dilatancy to thixotropy with shear rate, by assuming the equilibrium between the flow units. f = X1β1s./α1 + 1/(1+Kexp(c0s.2/RT))((1-X1)/α2)sinh-1{(β2)0 s. exp(c2s.2/RT)} + K exp(c0s.2/RT)/(1+K exp(c0s.2/RT))((1-X1)/α3)sinh-1{(β3)0 s. exp(-c3s.2/RT)} By applying this flow equation to the experimental flow curves for the concentrated starch-water suspensions, the flow parameters were obtained. And, by substituting the obtained flow parameters to the flow equation, the theoretical flow curves were reproduced. Also, Ostwald curve was represented by applying the flow equation, and the applicability for stress relaxation was discussed.