• The Korean Journal of Rheology
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• v.10 no.4
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• pp.234-246
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• 1998

The objective of this study is to investigate the correlation between steady shear flow (nonlinear behavior) and dynamic viscoelastic (linear behavior) properties for concentrated polymer solutions. Using both an Advanced Rheometic Expansion System(ARES) and a Rheometics Fluids Spectrometer (RFS II), the steady shear flow viscosity and the dynamic viscoelastic properties of concentrated poly(ethylene oxide)(PEO), polyisobutylene(PIB), and polyacrylamide(PAAm) solutions have been measured over a wide range of shear rates and angular frequencies. The validity of some previously proposed relationships was compared with experimentally measured data. In addition, the effect of solution concentration on the applicability of the Cox-Merz rule was examined by comparing the steady flow viscosity and the magnitude of the complex viscosity Finally, the applicability of the Cox-Merz rule was theoretically discussed by introducing a nonlinear strain measure. Main results obtained from this study can be summarized as follows : (1) Among the previously proposed relationships dealt with in this study, the Cox-Merz rule implying the equivalence between the steady flow viscosity and the magnitude of the complex viscosity has the best validity. (2) For polymer solutions with relatively lower concentration, the steady flow viscosity is higher than the complex viscosity. However, such a relation between the two viscosities is reversed for highly concentrated polymer solutions. (3) A nonlinear strain measure is decreased with increasing stran magnitude, after reaching the maximum value in small strain range. This behavior is different from the theoretical prediction demonstrating the shape of a damped oscillatory function. (4) The applicability of the Cox-Merz rule is influenced by the $\beta$ value, which indicates the slope of a nonlinear stain measure (namely, the degree of nonlinearity) at large shear deformations. The Cox-Merz rule shows better applicability as the $\beta$ value becomes smaller.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1175-1179
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• 1999

The rheological properties of highly filled epoxy molding compound(EMC) for semi-conductor encapsulants are greatly affected by the content of filler loaded. In this study, the change of viscosity of EMC for semi-conductor encapsulants with the filler content was investigated. Also, both of Cox-Merz and modified Cox-Merz equations were applied to convert the viscosity change as a function of frequency to that of shear rate. It was ovserved that shear thinning and yield stress occured at high filler contents and that the Cox-Merz equation could not be applied at high filler contents because of the difference of viscosity according to the various strains. When the modified Cox-Merz equation was applied, the all the curves having different strain tend to be represented by one master curve, even though some deviation was obseved at high filler content and strain.

• Proceedings of the Korean Fiber Society Conference
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• 1997.04a
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• pp.186-189
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• 1997

• Journal of the Korean Society of Food Science and Nutrition
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• v.29 no.5
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• pp.860-864
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• 2000

The steady and dynamic shear rheological properties of traditional kochujang fermented at three different temperatures (20${^circ}C$, 25${^circ}C$ and 30${^circ}C$) were studied. Flow of kochujang samples showed time dependence, which was quantitatively described by the Weltman model, Kochujang samples were highly shear thinning fluids (n=0.25~0.27) with large magnitudes of Casson yield stresses (1.09~1.21 kPa). Consistency index (K) and apparent viscosity (${\eta}_{a,20}$) increased with increase in fermentation temperature of kochujang. Storage (G') and loss (G") moduli increased with increase in frequency (ω), while complex viscosity (${\eta}^{\ast}$) decreased. Based on dynamic shear data, kochujang samples exhibit structural properties similar to weak gels. The complex and steady shear viscosities at different fermentation temperatures followed the Cox-Merz superposition rule with the application of the shift factor (a=0.011~0.016).

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.169-173
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• 2004

The control of the rheological properties of a fluid during processing is important and can determine the efficiency of the production in addition to the performance of the final product. The vast majority of process fluids are viscoelastic, hence an instrument that measures both the viscous and elastic properties of the material during processing would be of great practical use. However, most in-line instruments commercially available to date are only capable of measuring viscosity at a single shear rate. An in-line rheometer that measures both the viscous and elastic properties of fluids over a wide range of shear rates simultaneously has been described in a previous publication (Glasscock et at., 2003) in which the results of measurements on flowing sunflower oil were presented. Before this instrument can be used in an industrial situation, it must be demonstrated that the generated results are the same as, or bear some fixed relationship to, the results obtained by conventional off-line rheometers. To this end, the present investigation describes the measurements of a standard reference fluid, polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane, labelled SRM2490 by the National Institute of Standards and Technology (NIST) in the USA. The results obtained using the in-line rheometer show remarkably good correlation for viscosity, using a modified Cox­Merz rule, with the results supplied with the reference material from NIST.

• Food Science and Biotechnology
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• v.15 no.6
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• pp.871-876
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• 2006

Rheological behavior of commercial hot pepper-soybean paste (HPSP) was evaluated in small amplitude oscillatory and steady shear tests. Storage modulus (G'), loss modulus (G"), and complex viscosity (${\eta}^*$) as a function of angular frequency (${\omega}$), and shear stress (${\sigma}$) as a function of shear rate (${\gamma}$) data were obtained for 5 commercial HPSP samples. HPSP samples at $25^{\circ}C$ exhibited a non-Newtonian, shear-thinning flow behavior with high yield stresses and their flow behaviors were described by power law, Casson, and Herschel-Bulkley models. Time-dependent flow properties were also described by the Weltman, Hahn, and Figoni & Shoemaker models. Apparent viscosity over the temperature range of $5-35^{\circ}C$ obeyed the Arrhenius temperature relationship with activation energies (Ea) ranging 18.3-20.1 kJ/mol. Magnitudes of G' and G" increased with an increase in ${\omega}$, while ${\eta}^*$ decreased. G' values were higher than G" over the most of the frequency range (0.63-63 rad/sec), showing that they were frequency dependent. Steady shear viscosity and complex viscosity of the commercial HPSP did not fit the Cox-Merz rule.

• Korean Journal of Food Science and Technology
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• v.33 no.6
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• pp.700-705
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• 2001

Sucrose첨가가 옥수수 전분호액의 레올로지 특성에 미치는 영향에 대하여 평가하였다. 전분호액은 sucrose 첨가에 관계없이 전단담화 비뉴턴 거동(n=0.37-0.58)을 나타내었으며, 또한 sucrose의 농도가 증가함에 따라 점조도지수$(K,\;K_h)$, 겉보기 점도$({\eta}_{a,100})$값은 크게 감소하였고 항복응력$({\sigma}_{oc},\;{\sigma}_h)$도 감소하는 경향을 나타내었다. 전분호액의 겉보기점도에 대한 온도의존성은 Arrhenius식에 의하여 높은 상관관계를 나타내었으며, 활성화에너지는 각각 10.80-15.59 kJ/mole을 나타내었고 농도가 증가함에 따라 감소하는 경향을 나타내었다. 적용된 주파수$({\omega})$ 범위에서 저장탄성률(G#)의 수치가 손실탄성률(G@)보다 높게 나타났으며 sucrose의 농도가 증가함에 따라 감소하여 탄성 및 점성 성질을 감소시켜 주었다. 이들 동적데이터로부터 전분호액은 sucrose 첨가에 의해 더욱 약한 겔과 같은 구조적 성질을 나타냄을 알 수 있었다. 그러므로 sucrose 첨가는 전분호액 내의 입자들의 재회합을 방해하여 전분호액의 레올로지 특성을 변화시킨다. Sucrose 30%를 첨가한 옥수수 전분호액을 제외한 모든 시료들은 이동인자$(shift\;factor,\;\alpha)$를 사용함으로써 Cox-Merz 중첩 원리에 잘 적용되었다.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.140-143
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• 1998

고분자 가공에서의 실제 공정 조건인 대변형하에서의 가공원액(고분자용융체 또는 농후용액)의 응답특성은 완제품의 기계적 또는 물리적 성질에 큰 영향을 미친다. 그러므로 고분자 액체의 유변학적 성질파악이 중요하며, 그 측정방법은 크게 정상전단실험과 동적전단실험으로 대별할 수 있다. 그러나 정상전달실험시에는 높은 전단속도하에서의 전단가열과 동시에 시료분해가 발생할 수 있다.(중략)

• Korean Journal of Food Science and Technology
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• v.40 no.2
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• pp.184-189
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• 2008

Effects of sucrose at different concentrations (0, 10, 20, and 30%, w/w) on steady and dynamic shear rheological properties of sweet potato starch (SPS) paste (5%, w/w) were investigated. The steady shear rheological properties of SPS-sucrose composites were determined from rheological parameters based on power law and Casson flow models. At 25$^{\circ}C$ all the samples showed pseudoplastic and thixoropic behavior with high yield stress. Consistence index (K), apparent viscosity (${\eta}_{a,100}$), and yield stress (${\sigma}_{oc}$) values of SPS-sucrose composites decreased with increasing sucrose concentration from 10% to 30%. The decrease of swelling power was observed at higher sucrose concentration (>20%) and the low swelling power yielded a lower K, ${\eta}_{a,100}$, and ${\sigma}_{oc}$ values. In temperature range of 25-70$^{\circ}C$, Arrhenius equation adequately assessed variation with temperature. Oscillatory test data showed weak gel-like behavior. Magnitudes of storage (G') and loss (G") moduli increased with an increase in sucrose concentration and frequency. The SPS-sucrose composite at 30% concentration closely followed the Cox-Merz superposition rule.

• Preventive Nutrition and Food Science
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• v.14 no.3
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• pp.233-239
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• 2009

The effects of guar gum (GG) and xanthan gum (XG) at different concentrations (0, 0.2, 0.4, and 0.6% w/w) on the rheological properties of Korean waxy rice starch (WRS) pastes were evaluated under both steady and dynamic shear conditions. The flow properties of WRS-gum mixtures were determined from the rheological parameters of the power law model. The addition of GG and XG to WRS resulted in an increase in the apparent viscosity ($\eta_{a,100}$) and consistency index (K) values obtained from power law model. The flow behavior index (n) values of the WRS-XG mixtures decreased with an increase in gum concentration while there was only a marginal difference between n values for the WRS-GG mixtures. Dynamic moduli (G', G", and $\eta^*$) values in the WRS-gum mixture systems also increased with an increase in gum concentration. WRS-XG mixtures had higher dynamic moduli and lower tan $\delta$ (ratio of G"/G') values than WRS-GG mixtures, indicating that the higher dynamic rheological properties of WRS-XG can be attributed to an increase in the viscoelasticity of the continuous phase in the starch-gum mixture systems, which was due to the higher viscoleastic properties of XG compared to GG. The dynamic ($\eta^*$) and steady shear ($\eta_a$) viscosities of the WRS-XG paste at a 0.2% gum concentration followed the Cox-Merz superposition rule.