• Korea-Australia Rheology Journal
• /
• v.20 no.3
• /
• pp.109-116
• /
• 2008

The effect of intermolecular aggregation induced by hydrophobic and electrostatic interactions on shear and elongational flow properties of aqueous acrylic thickener solutions is discussed. Complex shear modulus is determined at frequencies up to $10^4$ rad/s employing oscillatory squeeze flow. Extensional flow behavior is characterized using Capillary Break-up Extensional Rheometry. Aqueous solutions of poly(acrylic acid)(PAA)/poly(vinylpyrrolidone-co-vinylimidazole) (PVP-VI) mixtures exhibit unusual rheological properties described here for the first time. Zero-shear viscosity of the mixtures increases with decreasing pH and can exceed that of the pure polymers in solution by more than two orders of magnitude. This is attributed to the formation of complexes induced by electrostatic interactions in the pH range, where both polymers are oppositely charged. PAA/PVP-VI mixtures are compared to the commercial thickener Sterocoll FD (BASF SE), which is a statistical co-polymer including (meth) acrylic acid and ethylacrylate (EA) forming aggregates in solution due to "sticky" contacts among hydrophobic EA-sequences. PAA/PVP-VI complexes are less compact and more deformable than the hydrophobic Sterocoll FD aggregates. Solutions of PAA/PVP-VI exhibit a higher zero-shear viscosity even at lower molecular weight of the aggregates, but are strongly shear-thinning in contrast to the weakly shear-thinning solutions of Sterocoll FD. The higher ratio of characteristic relaxation times in shear and elongation determined for PAA/PVP-VI compared to Sterocoll FD solutions reflects, that the charge-induced complexes provide a much stronger resistance to extensional flow than the aggregates formed by hydrophobic interactions. This is most likely due to a break-up of the latter in extensional flow, while there is no evidence for a break-up of complexes for PAA/PVP-VI mixtures. These flexible aggregates are more suitable for the stabilization of thin filaments in extensional flows.

• The Korean Journal of Rheology
• /
• v.7 no.3
• /
• pp.181-191
• /
• 1995

점탄성유체의 물성치들 중 정압열팽창계수 및 밀도는 자연대류 열전달 연구에 전단 속도 0에서의 점도는 점탄성유체에 대한 모델들 사용 시 필요하다. 본 연구에서는 점탄성유 체이며 마찰 감소 첨가제, 유전자 분리용액동으로 사용하는 Separan AP-273 용액의 정압열 팽창계수, 밀도 및 전단속도 0에서의 점도에대한 농도 및 온도의 영향을 조사하였다. 작동유 체의 물성치들은 10~6$0^{\circ}C$의 온도범위와 100~20,000wppm의 농도범위에서 측정되었다. 작 동유체의 물성치들에 미치는 열주기와 노화의 영향을 조사하기 위해서 정압열팽창계수와 전 단속도 0에서의 점도를 교대로 두 번씩 측정했다. 정압열팽창계수 및 밀도를 측정하는 장치 의 측정 정밀도는 증류수에 대한 측정치와 문헌에 나타난 자료를 비교하여 얻었고 이는 $\pm$ 2%이내였다. Separan AP-273용액의 정압열팽창계수 및 밀도는 증류수의 값들로 대치될수 있다. 작동유체의 정압열팽창계수와 밀도는 열주기와 노화의 영향을 받지 않았다. 낙하식 점 도계를 사용해 측정한 겉보기점도 값들을 나타내느 flow curve에서 전단속도가 0이 되는방 향으로 겉보기점도를 외삽시켜 Separan AP-273용액에 대한 전단속도0에서의 점도를 얻었 다. 정압열팽창계수 측정 전후에 측정한 작동유체에 대한 전단속도 0에서의 점도는 열주기 와 노화로 인해 퇴화되었다.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.16 no.3
• /
• pp.181-192
• /
• 2012

Here in this paper, the steady paint film flow on a vertical wall of a non-Newtonian pseudo plastic fluid for drainage problem has been investigated. The exact solution of the nonlinear problem is obtained for the velocity profile. Also the average velocity, volume flux, shear stress on the wall, force to hold the wall in position and normal stress difference have been derived. We retrieve Newtonian case, when material constant ${\mu}_1$ and relaxation time ${\lambda}_1$ equal zero. The results for co-rotational Maxwell fluid is also obtained by taking material constant ${\mu}_1$ = 0. The effect of the zero shear viscosity ${\eta}_0$, the material constant ${\mu}_1$, the relaxation time ${\lambda}_1$ and gravitational force on the velocity profile for drainage problem are discussed and plotted.

• Journal of Pharmaceutical Investigation
• /
• v.29 no.3
• /
• pp.193-203
• /
• 1999

In order to investigate systematically the steady shear flow properties of aqueous po1y(ethylene oxide) (PEO) solutions having various molecular weights and concentrations, the steady flow viscosity has been measured with a Rheometrics Fluids Spectrometer (RFS II) over a wide range of shear rates. The effects of shear rate, concentration, and molecular weight on the steady shear flow properties were reported in detail from the experimentally measured data, and then the results were interpreted using the concept of a material characteristic time. In addition, some flow models describing the non-Newtonian behavior (shear-thinning characteristics) of polymeric liquids were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was examined by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) At low shear rates, aqueous PEO solutions show a Newtonian viscous behavior which is independent of shear rate. At shear rate region higher than a critical shear rate, however, they exhibit a shear-thinning behavior, demonstrating a decrease in steady flow viscosity with increasing shear rate. (2) As an increase in concentration and/or molecular weight, the zero-shear viscosity is increased while the Newtonian viscous region becomes narrower. Moreover, the critical shear rate at which the transition from the Newtonian to shear-thinning behavior occurs is decreased, and the shear-thinning nature becomes more remarkable. (3) Aqueous PEO solutions show a Newtonian viscous behavior at shear rate range lower than the inverse value of a characteristic time $1/{\lambda}_E$, while they exhibit a shear-thinning behavior at shear rate range higher than $1/{\lambda}_E$. For aqueous PEO solutions having a broad molecular weight distribution, the inverse value of a characteristic time is not quantitatively equivalent to the critical shear rate, but the power-law relationship holds between the two quantities. (4) The Cross, Carreau, and Carreau-Yasuda models are all applicable to describe the steady flow behavior of aqueous PEO solutions. Among these models, the Carreau-Yasuda model has the best validity.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.25 no.4
• /
• pp.41-50
• /
• 2017

The design of proper agitation system is requisite in biological waste treatment and energy generation plant, which is affected by viscosity, impeller types, and power consumption. In the present work, hydrogen fermentation of food waste was conducted at various operational pHs (4.5~6.5) and substrate concentrations (10~50 g Carbo. COD/L), and the viscosity of fermented broth was analyzed. The $H_2$ yield significantly varied from 0.51 to $1.77mol\;H_2/mol\;hexose_{added}$ depending on the pH value, where the highest performance was achieved at pH 5.5. The viscosity gradually dropped with shear rate increase, indicating a shear thinning property. With the disintegration of carbohydrate, the viscosity dropped after fermentation, but it did not change depending on the operational pH. At the same pH level, the $H_2$ yield was not affected much, ranging $1.40{\sim}1.86mol\;H_2/mol\;hexose_{added}$ at 10~50 g Carbo. COD/L. The zero viscosity and infinite viscosity of fermented broth increased with substrate concentrations, from 10.4 to $346.2mPa{\cdot}s$, and from 1.7 to $5.3mPa{\cdot}s$, respectively. There was little difference in the viscosity value of fermented broth at 10 and 20 g Carbo. COD/L. As a result of designing the agitation intensity based on the experimental results, it is expected that the agitation intensity can be reduced during hydrogen fermentation. The initial and final agitation intensity of 30 g Carbo. COD/L in hydrogen fermentation were 26.0 and 10.0 rpm, respectively. As fermentation went on, the viscosity gradually decreased, indicating that the power consumption for agitation of food waste can be reduced.

• Journal of applied mathematics & informatics
• /
• v.39 no.5_6
• /
• pp.813-823
• /
• 2021

In this work, we present the classical formulation for the antiplane problem of a eletro-viscoelastic materialswith total sliprate dependent friction and write the corresponding variational formulation. In the second step, we prove that the solution converges to the solution of the corresponding electro-elastic problem as the viscosity converges to zero.

• Korean Journal of Food Science and Technology
• /
• v.31 no.3
• /
• pp.870-874
• /
• 1999

농후한 점도영역에서 감귤류 펙틴용액에 NaCl을 첨가하였을 때 점도 및 점탄성 변화를 연구하였다. NaCl의 농도가 증가함에 따라 펙틴용액의 점도도 점차 증가하였으며, 1.5 M의 NaCl을 첨가한 경우 점도가 약 3배 증가하였다. NaCl의 첨가에 따른 점도특성의 일반화 곡선으로서 ${\eta}/{\eta}_0$ 대 $\dot{\gamma}/\dot{\gamma}_{0.8}$ 관계는 상대적으로 낮은 중첩도를 보였다. Zero-shear viscosity $({\eta}_0)$와 NaCl 농도(C)와는 ${\eta}_0\;{\propto}\;10^{0.32C}$의 관계를 보였으며, 이때 상관계수(R2)는 0.995였다. 한편, NaCl 농도가 증가함에 따라 저장탄성률(G#)과 손실탄성률(G@)이 모두 증가하였다.

• Korea-Australia Rheology Journal
• /
• v.17 no.2
• /
• pp.35-40
• /
• 2005

Nanofluid is a novel heat transfer fluid prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. In this research we have considered the rheological properties of nanofluids made of CuO particles of 10-30nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement. When examined using TEM, individual CuO particles have the shape of prolate spheroid of the aspect ratio of 3 and most of the particles are under aggregated states even after sonication for a prolonged period. From the rheological property it has been found that the volume fraction at the dilute limit is 0.002, which is much smaller than the value based on the shape and size of individual particles due to aggregation of particles. At the semi-dilute regime, the zero shear viscosity follows the Doi-Edwards theory on rodlike particles. The thermal conductivity measurement shows that substantial enhancement in thermal conductivity with respect to particle concentration is attainable only when particle concentration is below the dilute limit.

• The Korean Journal of Rheology
• /
• v.1 no.1
• /
• pp.54-62
• /
• 1989

준희박과 농축용액에서 약간의 유연성을 갖는 강성막대형 고분자의 회전확산계수와 zero shear rate 점도를 예측하기 위해 한정된 강성 사슬모델이 제시되었다. 본 연구에서는 이제시된 모델을 분자량 분포를 갖는 다분산계로 확장시켰다. 분자들의 분자량 분포 (MW/Mn) 와 분포 함수를 알수 없기 때문에 해당분자에 가장 적당한 분자량 분포와 함수를 취하였다. 만약 이것들을 알고 있다면 제시된 모델로 회전확산계수와 zero shear rate 점도 등과 같은 인자들을예측할수 있었다. 단분산계의 경우와 같이 다분산계에서도 회전확산계수 의 평균분자 윤곽길이 의존도는 L-7 에 비례하는 것으로 나타났다. Doi와 Edwards 의 튜브 모델에 의한 L-9 과 다른 이유는 분자들의 거동을 관찰하기 위해 임의로 선정된 하나의 막 대형 고분자운동을 제약하는 정도가 심하지 않았으며 따라서 제약 완화시간도 훨씬 짧았기 때문이다. 더구나 점도와 회전 확산계수와 단분산계에서는 정성적으로 일치한데 제약 완화 시간도 훨씬 짧았기 때문이다. 더구나 점도와 회전적인 일치를 나타내었다. 이 모델로 기준 으로 하여 분자들의 길이와 종류에 관계없이 하나의 master curve를 그릴수 있었다.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.23 no.2
• /
• pp.1-14
• /
• 2005

Generally, printing inks are composed of pigment, vehicle and additive. Among others, the vehicle transfers the pigment to substrate and then binds it on the surface. So, rheological properties of the vehicle are an important factor which has influence on printability. Thus, in this study, rheology of the vehicle was investigated by using rotational rheometer according to molecular weight of resin. Also, emlusion rheology of water in oil type and its microstructure were examined with increasing the shear rate. Consequently, the following results were obtained: (1) By viscometric flow test, zero shear viscosity and shear thinning index of vehicle increased with increasing the molecular weight of resin. (2) By relaxation and creep test, relaxation time and retardation time of vehicle increased with increasing the molecular weight of resin. (3) By frequency sweep test, crossover point of vehicle increased with increasing the molecular weight of resin. (4) G' and G" of emlusions increased with increasing the molecular weight by amplitude sweep test. (5) The shape of water drop in emlusions was changed to the capillary tube.