• Elastomers and Composites
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• 제44권3호
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• pp.336-342
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• 2009

1.0 wt% 소수성실리카를 안정제로 하는 현탁중합에 의하여 $75^{\circ}C$에서 개시제의 농도를 변화하며 합성한 폴리스티렌 (PS) 및 폴리뷰틸메타크릴레이트 (PBMA) 입자의 점도를 모세관 레오미터 (capillary rheometer)를 이용하여 측정하였다. 중량평균분자량이 66,500 g/mol인 PS 입자는 $190^{\circ}C$에서 측정한 경우 낮은 전단속도에서는 뉴톤 (Newtonian) 거동을 나타내었다. PS 입자의 경우 분자량이 증가할수록 전단속도 전 영역에서 전단 묽어짐 (shear thinning) 거동을 보였다. PBMA 입자는 $170^{\circ}C$에서 점도를 측정하였으며 중량평균분자량이 156,700 g/mol 인 경우 낮은 전단속도에서만 뉴톤 거동을 나타내었다. 분자량의 증가에 따라 전단 묽어짐 거동이 관찰되었으며, 이러한 변화의 형태는 PS 입자와 유사하였다. 카본블랙을 충전제로 합성한 고분자 복합체 입자의 전단점도는 PS 및 PBMA 둘 다 $170^{\circ}C$에서 측정하였다. PS 및 PBMA 복합체 입자의 점도변화는 카본블랙의 증가에 따라 점진적으로 증가하였으나, 충전제의 증가에 따른 점도의 증가는 분자량의 증가 효과에 비교하여 미약하였다. 내부혼합기를 이용하여 제조한 카본블랙을 함유하는 PS 복합체의 점도변화는 현탁중합법으로 합성한 카본블랙을 함유하는 PS 복합체 입자의 점도변화에 비하여 작았으며 이는 향상된 분산으로 인하여 발생한 것으로 추정된다. 이 실험에서 선택한 분자량 및 카본블랙의 농도에서 yield 거동은 관찰되지 않았다.

• 문화기술의 융합
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• 제9권4호
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• pp.331-335
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• 2023

혈액의 점도가 높아질수록 혈액은 더 끈적하고 흐름이 어려워지므로 혈전의 발생 가능성이 높아져 허혈성 뇌경색의 발생 확률이 증가한다. 혈액 점도 측정은 최근 순환기계 질환의 예방을 위하여 그 중요성이 강조되고 있으며 혈액의 점도를 쉽고 정확하게 측정할 수 있는 점도계의 필요성이 대두되고 있다. 본 연구에서는 평행판 점도계 ARS-Medi에 의한 점도표준액과 인공혈액의 측정값들을 국제적으로 정확성과 신뢰성을 인정받는 TA instrument의 Ares-G2로 측정한 값들과 비교하였다.. 뉴턴성 용액인 N44 표준용액의 점도는 모든 전단율에서 두 기기 간에 거의 완벽하게 일치하였다, 비뉴턴성 용액인 인공혈액의 경우 가장 낮은 전단율인 1 rad/s 에서는 약 10%의 차이를 보였으나, 임상적으로 유의한 전단율인 10 rad/s 이상에서는 두 기기간의 측정값이 오차범위 내에서 모두 일치하였다. 우리는 새로 개발한 혈액 전용 평행판형 점도계 ARS-Medi가 1회용 평행판을 사용하므로 혈액 점도 측정의 편의성과 위생성이 향상되어 임상에 매우 유용할 것으로 기대한다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.377-382
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• 2010

젤 추진제와 유변학적 특성이 유사한 모사 젤 추진제를 물, Carbopol 941, NaOH 농축액을 혼합하여 제작하였고, $Al_2O_3$ 나노 입자를 첨가하여 점도 특성을 비교하였다. 두 가지 모사 추진제의 물성치를 바탕으로 곡관 덕트 내에서의 유동특성을 수치모사하여 해석하였고 덕트에 Dean vortices가 발생하는 임계 Dean 수를 도출하였다. 젤-나노 추진제의 경우 비록 높은 겉보기 점성계수를 가지나 젤 추진제와 비교시 같은 범위의 임계 Dean 수가 도출되었다. 이는 Fellouah et al.[1]이 제시한 바와 같이 비슷한 값의 Power law 지수에 기인하는 것으로 판단된다.

• 대한화학회지
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• 제58권3호
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• pp.251-257
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• 2014

Poly(methyl acrylate)-poly(acrylonitrile) 공중합체의 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하여 여러 온도의 공기 중, 증류수 용액에서 실행하였다. Eyring-Halsey 모델의 이론적인 응력완화식에 응력완화 실험 결과를 적용하여 여러 가지 유동 파라메타를 계산하였다. 비결정성 영역에서의 유동단위의 고찰을 위하여 유동 파라메타와 결정크기로부터 섬유고분자 물질의 자체확산, 홀 부피, 점성, 열역학파라메타 등을 계산하였다. 이들 시료의 유동 파라메타는 유동 단위의 홀부피, 자체확산, 유동 열역학 파라메타와 직접적인 연관을 갖는 것으로 규명되었다.

• 대한기계학회논문집A
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• 제30권1호
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• pp.32-41
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• 2006

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder.

• Journal of Pharmaceutical Investigation
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• 제33권1호
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• pp.15-19
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• 2003

The rheological behavior of poloxamer 407 solution as function of concentration and temperature was evaluated by rotational viscometer. The viscosity of poloxamer 407 solution was increased as the concentration of poloxamer 407 and temperature increased. At $4^{\circ}C$, poloxamer 407 solution showed the Newtonian flow characteristics regardless of concentration. Upon increasing temperature the poloxamer solution changed to the pseudoplastic flow pattern. And at gelation temperature, rheological profiles showed the abrupt increase in viscosity. Gelation temperature was decreased as the concentration of poloxamer 407 increased, while it increased as the concentration of poly(ethylene glycol) 4000 increased. Poly(ethylene glycol) might be expected to reduce the driving force for hydrophobic interaction resulting in slow gelation. From the viscoelastic properties of poloxamer gel system, we obtained the storage and loss modulus depending on the shear stress and frequency. And the sol-gel transition temperature was also obtained from the viscoelastic properties of poloxamer 407 gel.

• Macromolecular Research
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• 제15권4호
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• pp.291-301
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• 2007

The rheological behaviors and morphologies of polylactide (PLA) and chemically modified plasticized starch (CMPS) blends were investigated. For this study, oscillatory shear flow measurements of the PLA, CMPS and their blends were performed. A scanning electron microscope (SEM) study was also conducted on the extracted extrudates of the blends. The morphology of the blend changed in relation to the composition: sphere-shaped CMPS disperse/continuous PLA, rod-like deformed CMPS phase/continuous PLA, a co-continuous structure with bridged CMPS long rods and PLA dispersed/continuous CMPS. The composition of the phase inversion could be estimated and closely coincided from the observed morphology experimental results. The rheological behavior of the blends, from oscillatory measurements, was found to vary in relation to the composition, and reflected the morphologies of the blends. PLA showed Newtonian flow behavior, while CMPS showed strong shear thinning behavior. The relationships between the morphology and rheological properties were observed in detail.

• Preventive Nutrition and Food Science
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• 제22권1호
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• pp.56-61
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• 2017

Rheological properties of waxy barley flour (WBF) dispersions mixed with various gums (carboxyl methyl celluleose, guar gum, gum arabic, konjac gum, locust bean gum, tara gum, and xanthan gum) at different gum concentrations were examined in steady and dynamic shear. WBF-gum mixture samples showed a clear trend of shear-thinning behavior and had a non-Newtonian nature with yield stress. Rheological tests indicated that the flow and dynamic rheological parameter (apparent viscosity, consistency index, yield stress, storage modulus, and loss modulus) values of WBF dispersions mixed with gums, except for gum arabic, were significantly higher than those of WBF with no gum, and also increased with an increase in gum concentration. In particular, konjac gum at 0.6% among other gums showed the highest rheological parameter values. Tan ${\delta}$ values of WBF-xanthan gum mixtures were lower than those of other gums, showing that there is a more pronounced synergistic effect on the elastic properties of WBF in the presence of xanthan gum. Such synergistic effect was hypothesized by considering thermodynamic compatibility between xanthan gum and WBF. These rheological results suggest that in the WBF-gum mixture systems, the addition of gums modified the flow and viscoelastic properties of WBF, and that these modifications were dependent on the type of gum and gum concentration.

• Food Science and Biotechnology
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• 제15권2호
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• pp.264-269
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• 2006

Basic rheological data of dandelion leaf concentrates were determined to predict processing aptitude and usefulness of dandelion leaf concentrates as functional food materials. Hot water and 70% ethanol extracts of dandelion leaves were concentrated at 5, 20, and 50 Brix, and their static and dynamic viscosities, and Arrhenius plots were investigated. Most concentrated dandelion leaves extracted with hot water and 70% ethanol showed flow behaviors close to Newtonian fluid based on power law model evaluation. Apparent viscosity of concentrated dandelion leaves extracted with hot water and 70% ethanol decreased with increasing temperature. Yield stresses of concentrated dandelion leaves extracted with hot water and 70% ethanol by Herschel-Bulkley model application were 0.020-0.641 and 0.017-0.079 Pa, respectively. Activation energies of concentrated dandelion leaves extracted with hot water and 70% ethanol were $2.102-32.669{\times}10^3$ and $1.657-5.382{\times}10^3\;J/mol{\cdot}kg$ with increasing concentration, respectively. Loss modulus (G") predominated over storage modulus (G') at all applied frequencies, showing typical flow behavior of low molecular solution. G' and G" of concentrated dandelion leaves extracted with hot water slowly increased with increasing frequency compared to those of concentrated dandelion leaves extracted with 70% ethanol.

• Korea-Australia Rheology Journal
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• 제18권4호
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• pp.171-181
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• 2006

We present a short review for authors' previous work on direct numerical simulations for inertialess hard particle suspensions formulated either with a Newtonian fluid or with viscoelastic polymeric fluids to understand the microstructural evolution and the bulk material behavior. We employ two well-defined bi-periodic domain concepts such that a single cell problem with a small number of particles may represent a large number of repeated structures: one is the sliding bi-periodic frame for simple shear flow and the other is the extensional bi-periodic frame for planar elongational flow. For implicit treatment of hydrodynamic interaction between particle and fluid, we use the finite-element/fictitious-domain method similar to the distributed Lagrangian multiplier (DLM) method together with the rigid ring description. The bi-periodic boundary conditions can be effectively incorportated as constraint equations and implemented by Lagrangian multipliers. The bulk stress can be evaluated by simple boundary integrals of stresslets on the particle boundary in such formulations. Some 2-D example results are presented to show effects of the solid fraction and the particle configuration on the shear and elongational viscosity along with the micro-structural evolution for both particles and fluid. Effects of the fluid elasticity has been also presented.