• The Korean Journal of Rheology
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• v.10 no.3
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• pp.131-136
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• 1998

아역청탄을 이용하여 제조된 CWM(Coal-Water Mixture)연료의 유변학적 특성을 측 정함으로써 음이온 계면활성제 Temol-N, 안정제 Xanthan 및 전해질 등의 첨가제에 대한 성능을 평가하고 최적첨가조성을 결정하였다. 계면확성제의 흡착으로 인해 석탄입자는 음전 하를 띠게 되었고 표면에 전기이중층이 생성되었다. 전기 이중층의 전기적 반발력이 입자의 응집을 막았고 CWA 슬러리의 점도를 감소시켰다. 또한 Xanthan과 NaOH의 첨가로 인해 분산안정성 및 침강안정성이 향상되는 것을 관찰하였다. CWM에서 석탄입자가 차지하는 부 피비를 무게비로 전환하여 표현하고 분산계에서 입자의 부피비에 따른 점도변화를 예측하는 실험식인 Krieger-Dougherty 식과 Frankel-Acrivos 식에 적용하였다. 점도 실험값을 가지 고 식의 변수들을 결정해 본결과 CWM이 나타내는 점도의 석탄함량에 따른 변화를 위 식 들이 비교적 정확시 나타내 주는 것을 확인하였다.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.203-211
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• 2009

In flows with deformation rates larger than the inverse Rouse time of the polymer chain, chains are stretched and their confining tubes become increasingly anisotropic. The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic and limit chain stretch. In the Molecular Stress Function (MSF) model, chain stretch is balanced by an interchain pressure term, which is inverse proportional to the $3^{rd}$ power of the tube diameter and is characterized by a tube diameter relaxation time. We show that the tube diameter relaxation time is equal to 3 times the Rouse time in the limit of small chain stretch. At larger deformations, we argue that chain stretch is balanced by two restoring tensions with weights of 1/3 in the longitudinal direction of the tube (due to a linear spring force) and 2/3 in the lateral direction (due to the nonlinear interchain pressure), both of which are characterized by the Rouse time. This approach is shown to be in quantitative agreement with transient and steady-state elongational viscosity data of two monodisperse polystyrene melts without using any nonlinear parameter, i.e. solely based on the linear-viscoelastic characterization of the melts. The same approach is extended to model experimental data of four styrene-butadiene random copolymer melts in shear flow. Thus for monodisperse linear polymer melts, for the first time a constitutive equation is presented which allows quantitative modeling of nonlinear extension and shear rheology on the basis of linear-viscoelastic data alone.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.169-172
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• 2002

Silver pastes for inner conductor in the Low Temperature Co-fired Ceramics (LTCC) are composed of silver powder, binder, solvent and additives. The composition of the chemicals have influence on rheology, printability, shrinkage rate, etc. In this study, commercial Ag pastes and Ag pastes made in KETI were investigated to find the relationship between characteristics of Ag paste and solid contents. Ag pastes with 68~90 wt% Solid Contents were tested. Substrate/paste matching property and conductivity of the conductor lines showed large dependence on solid contents of Ag paste.

• Korea-Australia Rheology Journal
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• v.15 no.1
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• pp.43-50
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• 2003

In this study, two types of biodegradable resins-based clay nanocomposites, in which organic montmorillonite clay was filled, were prepared by the direct melt blending method. In order to characterize the nanocomposite structure, wide-angle X-ray diffraction (WAXD) and TEM observation were performed. Characterization of the nanocomposites shows that intercalated and partially exfoliated structures were generated by the melt blending method. Mechanical and rheological properties of the nanocomposites were measured respectively. For the mechanical properties, there were improvements in tensile strength and Young's modulus of the nanocomposites due to the reinforcement of nanoparticles. The rheological behaviors of the nanocomposites were significantly affected by the degree of the dispersion of the organoclay. The storage modulus of the nanocomposites was measured and the degree of the dispersion of the organoclay was evaluated from the value of the terminal slope of the storage modulus. In addition, the quantity of the shear necessary for making the nanocomposite for melt intercalation method was estimated from the relationship between the value of the terminal slope of the storage modulus and the applied shear.

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.61-66
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• 2007

The aggregation characteristics of red blood cells (RBCs) are known as important factors in the microvascular flow system, and increased RBC aggregation has been observed in various pathological diseases, such as thrombosis and myocardial infarction. This paper describes a simple microfluidic device for measuring the RBC aggregation by integrating a microfluidic slit rheometry and laser-backscattering technique. While a decreasing-pressure mechanism was applied to the microfluidic rheometry, a syllectogram (the light intensity versus time) showed an initial increase and a peak caused by the high shear stress-induced disaggregation, immediately followed by a decrease in the light intensity due to RBC aggregation. The critical shear stress (CST) corresponding to the peak intensity was examined as a new index of the RBC aggregation characteristics. The CST of RBCs increased with increasing aggregation-dominating protein (fibrinogen) in the blood plasma. The essential feature of this design was the combination of the rheometric-optic characterization of RBC aggregation with a microfluidic chip, which may potentially allow cell aggregation measurements to be easily carried out in a clinical setting.

• Journal of Dairy Science and Biotechnology
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• v.36 no.2
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• pp.73-80
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• 2018

The textural and rheological properties of cheese are major attributes for the characterization of cheese types, ripening, and consumer preferences. The use of small amplitude oscillatory rheological testing has made it possible for cheese researchers to assess the major properties of cheese, such as melting behavior and storage modulus, without irreversible deformation. In addition, large deformation testing such as textural profile analysis can assess properties such as hardness of cheese. While the sensory properties of cheese are valued by consumers, objective and reliable measurements are paramount for researchers. Ongoing development and refinement of scientific measurement methods of cheese are vital.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.1
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• pp.53-58
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• 2004

In this study, we describe the application of electron microscopes that incorporate freeze treatments or cryo systems to achieve the characterization of the microstuctures of emulsions. We confirmed that the preparations of freezing replica method and with cryo systems were useful to clarify the microstuctures of the emulsions. This methodology will be able to contribute to understanding the relation between microstuctures and rheology of emulsions.

• Journal of Magnetics
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• v.21 no.2
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• pp.261-265
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• 2016

Surface tension is a major factor in the thermodynamics as well as fluid properties of Magneto-Rheological Fluids (MRF). We measured the surface tension of an MRF using two different methods. A wettability characterization based on contact angles measurements for the fluid interacting with two different surfaces was conducted. A hydrocarbon based commercial MRF with more than 80% solid weight, placed on quartz and poly-tetra-fluoroethylene (PTFE) surfaces was used. We measured the fluids' surface tension value by means of contact angles measurements and by the falling drop method.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.213-223
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• 2009

Taylor-Couette flow (i.e., flow between concentric, rotating cylinders) has long served as a paradigm for studies of hydrodynamic stability. For Newtonian fluids, the rich cascade of transitions from laminar, Couette flow to turbulent flow occurs through a set of well-characterized flow states (Taylor Vortex Flow, wavy Taylor vortices, modulated wavy vortices, etc.) that depend on the Reynolds numbers of both the inner and outer cylinders ($Re_i$ and $Re_o$). While extensive work has been done on (a) the effects of weak viscoelasticity on the first few transitions for $Re_o=0$ and (b) the effects of strong viscoelasticity in the limit of vanishing inertia ($Re_i$ and $Re_o$ both vanishing), the viscoelastic Taylor-Couette problem presents an enormous parameter space, much of which remains completely unexplored. Here we describe our recent experimental efforts to examine the effects of drag reducing polymers on the complete range of flow states observed in the Taylor-Couette problem. Of particular importance in the present work is 1) the rheological characterization of the test solutions via both shear and extensional (CaBER) rheometry, 2) the wide range of parameters examined, including $Re_i$, $Re_o$ and Elasticity number E1, and 3) the use of a consistent, conservative protocol for accessing flow states. We hope that by examining the stability changes for each flow state, we may gain insights into the importance of particular coherent structures in drag reduction, identify simple ways of screening new drag reducing additives, and improve our understanding of the mechanism of drag reduction.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.128-134
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• 1999

Rheological characterization was examined for two different types of magenetic particle (rod-like $\gamma$-$Fe_{2}O_{3}$, $CrO_2$ )suspension in this study. The measured suspension viscosity (viscosity vs. concentration or shear rate) is used to obtain the dependence of viscous energy dissipation on the microstructural states of magnetic particle dispersions as well as the microstructural shape effects which are related to magnetic particle orientation. The empirical formulas from mean field theory and the Mooney equation are used to relate suspension viscosity to particle concentration. Intrinsic viscosities of these two different types of rod-like magnetic particle suspensions are found to exceed the prediction of hydrodynamic theory for dilute suspensions and support the existence of flocs containing significant amounts of immobilized suspending medium due to native attraction forces among particles in the microstructures.