• The Korean Journal of Rheology
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• v.10 no.1
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• pp.24-30
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• 1998

솔젤법을 이용하여 단분산의 실리카 입자를 제조하고 농도변화에 따른 실리카 분산 액의 유변학적 거동을 해석하였다. 단분산 실리카 입자의 제조는 솔젤법을 이용한 액상반으 으로 제조하였고 입자의 안정화를 위하여 입자표면에 실란커플링제를 코팅하여 유기용매에 서 안정성을 갖도록 하였다. 분산액의 농도에 따른 유변학적 거동을 조사하기 위하여 부피 분율( )이 0.05인 희박 분산계로부터 =0.55의 고농도 분산계를 제조하였다. 솔젤법을 통하 여 단분산 실리카 입자를 성공적으로 제조하였으며 실란커플링제인 ${\gamma}$-methacryloxypropyl triethoxysilane로 입자의 표면을 화학적 방법으로 처리하여 유기용매 상에서 알킬기의 작용 에 의한 hard-sphere'특성을 나타내도록 하였으며 동시에 분산안정성을 유지할수 있었다. 입자 분산계는 =0.25이하의 부피농도에서는 분산용매와 같은 뉴톤거동을 보여주었으며 이 이이상의 농도에서는 비뉴톤거동인 전단담화(shear thinning)현상과 high shear limiting viscosity를 나타내었다. 이결과는 Krieger-Dougherty 식을 따름이 확인되었으며 부피분율 =0.50정도까지도 이식이 잘적용됨을 확인하였다. 부피분율 =0.50 이상의 고농도 입자 분산계 는 급격한 점도의 증가와 함께 전단담화와 전단탁화(shear thickening)현상이 모두 관찰되었 다. 특히 전단탁화를 일으키는 특헝전단변형률(cr)이하의 전단변형률에서는 안정되고 빠른 점성반응(viscous response)을 보여주었으나 특성 전단변형률 부근과 이상의 전단변형률 영 역에서는 매우 불안한 거동이 보여짐을 확인하였다. 그러나 이러한 점도 거동은 가역적이며 전단변형률을 증가시킬때와 감소시킬 때의 유변학적 거동이 거의 일치하였다.

• The Korean Journal of Rheology
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• v.5 no.2
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• pp.136-143
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• 1993

PDSC(pressurized differential scanning calorimeter)를 이용하여 물 또는 물 -DMF(N,N-dimethylformamide) 혼합물을 함유한 아크릴로니크릴 중합체(wet-PAN)의 융점 거동을 조사하였으며 wet-PAN 용융체의 점도측정에 적합한 모세관형 점도계를 제작하여 전단속도 및 온도에 따른 점도변화를 고찰하였다. 물에 의한 wet-PAN의 융점 및 용융점도 는 물의 함량이 증가함에 따라 점근적으로 감소하여 25wt% 이상에서는 거의 일정하였다. 또한 물(25wt% 기준)의 일부를 DMF로 대체하였을 경우에는 융점이 감소하였다. 한편 wet-PAN의 용융점도는 power-law 거동에 준하였으며 물계에서는 power-law 지수(n)가 0.16(19$0^{\circ}C$)~0.18(17$0^{\circ}C$)인데 비하여 물(95)~DMF(5) 혼합물계에서는 0.24(175$^{\circ}C$)~0.25(16 5$^{\circ}C$)로서 점도의 전단담화거동이 약해졌으나 흐름의 활성화에너지는 다소 증가 하였다.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.49-61
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• 2011

This paper presents the applicability of rheological models for describing fine-laden debris flows and analyzes the flow characteristics as a function of grain size. Two types of soil samples were used: (1) clayey soils - Mediterranean Sea clays and (2) silty soils - iron ore tailings from Newfoundland, Canada. Clayey soil samples show a typical shear thinning behavior but silty soil samples exhibit the transition from shear thinning to the Bingham fluid as shear rate is increased. It may be due to the fact that the determination of yield stress and plastic viscosity is strongly dependent upon interstructrual interaction and strength evolution between soil particles. So grain size effect produces different flow curves. For modeling debris flows that are mainly composed of fine-grained sediments (<0.075 mm), we need the yield stress and plastic viscosity to mimic the flow patterns like shape of deposition, thickness, length of debris flow, and so on. These values correlate with the liquidity index. Thus one can estimate the debris flow mobility if one can measure the physical properties.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.81-92
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• 2011

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

• The Korean Journal of Rheology
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• v.10 no.1
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• pp.7-13
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• 1998

중량 평균 분자량이 1.22$\times$106이고 다분산도가 8.90이며 수분과 아밀로오스 함량이 각각 9.35%, 27%인 도토리 전분에 sucrose를 첨가하여 동적 유변학적 특성에 대한 온도와 농도의존성을 고찰하였다. AS(acorn starch)-sucrose 계의 점도는 전단속도가 증가하면 감 소하는 전단담화 현상을 나타내며 sucrose 농도가 증가할수록 점도가 증가하였고, Casson 식에 의해 얻어진 항복치는 sucrose 농도가 증가하면 증가하였다. 저장영률과 손실영률은 sucrose 농도가 증가하면 단일하게 증가하였고 손실 탄성률은 온도가 증가하면 감소하였다. DSC 측정자료를 zipper model에 적용시켜 본 결과 sucrose 농도가 증가할수록 zipper의 수 와 junc-tion zone의 수는 증가했으며 크기는 감소하였다. Sucrose는 전분과 수소결합을 형 성하여 용액내에서 가소제처럼 거동함을 알수있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.300-303
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• 2010

The present study investigates the flow characteristics of simulant gel propellant(carbopol 0.5%wt) in a variety of injectors. Rheological data for gel propellant has been measured and injector flow characteristics for plain-orifice, chamfered-orifice and venturi type injector have been numerically analyzed. The apparent viscosity of plain-orifice and chamfered-orifice have tendency to increase along axial direction, whereas for venturi type injector, low viscosity has been achieved in the injector flow. This phenomenon was clearly pronounced as Reynolds number is increased.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1227-1240
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• 2014

Abandoned mines often cause environmental problems, such as alteration of landscape, metal contamination, and landslides due to a heavy rainfall. Geotechnical and rheological tests were performed on waste materials corrected from Imgi waste rock dump, located in Busan Metropolitan City. Debris flow mobility was examined with the help of 1-D BING model which was often simulated in both subaerial and subaqueous environments. To determine flow curve, we used a vane-penetrated rheometer. The shear stress (${\tau}$)-shear rate (${\dot{\gamma}}$) and viscosity(${\eta}$)-shear rate (${\dot{\gamma}}$) relationships were plotted using a shear stress control mode. Well-known rheological models, such as Bingham, bilinear, Herschel-Bulkley, Power-law, and Papanastasiou concepts, were compared to the rheological data. From the test results, we found that the tested waste materials exhibited a typical shear shinning behavior in ${\tau}$-${\dot{\gamma}}$ and and ${\eta}$-${\dot{\gamma}}$ plots, but the Bingham behavior is often observed when the water contents increased. The test results show that experimental data are in good agreement with rheological models in the post-failure stage during shearing. Based on the rheological properties (i.e., Bingham yield stress and viscosity as a function of the volumetric concentration of sediment) of waste materials, initial flowing shape (5 m, 10 m, and 15 m) and yield stress (100 Pa, 200 Pa, 300 Pa, and 500 Pa) were input to simulate the debris flow motion. As a result, the runout distance and front velocity of debris flow are in inverse propositional to yield stress. In particular, when the yield stress is less than 500 Pa, most of failed masses can flow into the stream, resulting in a water contamination.

• Composites Research
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• v.21 no.2
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• pp.15-24
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• 2008

In this study, shear thickening fluid (STF) filled with rigid nano silica particles was impregnated in plain woven Kevlar fabrics to improve the impact resistance performance. The nano silica particles with an average diameter of 100nm, 300nm, and 500nm were used to make shear thickening fluid to estimate the effect of particle size on the impact behavior of STF impregnated Kevlar fabrics. The yam pull-out and frictional tests were conducted to estimate the effect of impregnated STF on the frictional characteristics. The test results showed that the friction forces were dramatically increased at the STF onset shear strain rates that were measured in preliminary rheology tests. The low speed impact tests were performed using the drop test machine. The results showed that the impregnated STF improved the impact resistance performance of the Kevlar fabrics in terms of the impact energy absorption and the deformation. It has been shown through tests that the impregnated STF affects the interfacial friction which contributes to improve the energy absorption in the Kevlar fabrics. Especially, the impregnation of the STF with the smaller particle size into the Kevlar fabrics showed the better performance in impact energy absorption.

• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.314-319
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• 2011

In this study, the flow behavior of Newtonian and non-Newtonian coating liquids inside slot die has been scrutinized for the purpose of optimal internal die design in slot coating system from three-dimensional computations by CFD Fluent solver. A hybrid slot die could be optimally designed by changing the chamber or manifold structure to guarantee the uniform velocity distribution of coating liquids at die exit. Especially, for the non-Newtonian coating liquids, the length of coat-hanger for the uniform coating has been properly chosen, according to the degree of their shearthinning properties.

• 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.