• 한국식품과학회지
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• 제27권5호
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• pp.799-806
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• 1995

고유점도가 3.75 dL/g인 감귤류 펙틴 용액의 전단점도 및 점탄성에 대한 농도의존성을 연구하였다. 전형적인 자수법칙 흐름 현상이 2.0% 이상의 펙틴 농도에서 관찰되었으며, 전단점도의 전단속도 의존성은 농도의 증가에 따라 더욱 뚜렷하게 나타났다. ${\eta}_{sp.o}$ 대 $C[\eta]$를 양대수 좌표에 그렸을 때 묽은 영역에서 진한 영역으로의 전이를 나타내는 $C^{*}[\eta]$는 약 4.0이었으며, 이때 ${\eta}_{sp.o}$의 값은 약 10.0을 나타내었다. 묽은 용액$(C[\eta]과 진한 용액$(C[\eta]>C^{*}[\eta])$에서 ${\eta}_{sp.o}$ $C[\eta]$의 기울기는 각각 1.1과 4.5였다. 전단점도를 ${\eta}/{\eta_0}$ 대 ${\gamma}/{\gamma}_{0.8}$에 대하여 그렸을 때 $2{\sim}5%$의 농도에서는 잘 중첩되었으나, 6%의 고농도에서는 중첩곡선에서 벗어나는 현상을 보였다. 펙틴 용액의 점탄성을 조사한 결과 전 농도범위에서 손실탄성률$(G^{\prime\prime})$의 값이 저장탄성률$(G^\prime)$보다 훨씬 높은 값을 보여 점성이 전체 점탄성을 지배하는 것으로 나타났다. 저 농도에서 전단점도는 복소점도와 거의 비슷한 값을 보여 Cox-Merz 법칙에 잘 부합하였으나, 농도가 높아질수록 두 값은 차이를 보였다.

• 폴리머
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• 제34권5호
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• pp.415-423
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• 2010

고검화도(98%이상)의 폴리(비닐 알코올)(PVA)를 디메틸설폭사이드(DMSO) 용매에 녹인 뒤 PVA 준희박 용액 대에서 농도 $C{\simeq}0.14\;g/mL$까지 점성도를 측정하였으며, 이 시스템을 매트릭스로 하여 폴리스티렌(PS) 라텍스 입자의 확산운동 지연을 동적 광산란법으로 조사하였다. PVA/DMSO계의 점성도를 고유점성도 $[{\eta}]$로 스케일된 환산농도 $C[{\eta}]$에 대하여 도시하였을 때 C$[{\eta}]$ >2에서는 분자량 의존성이 강하게 나타났으며, 그 원인은 PVA 용액 내에 존재하는 불균일 영역때문인 것으로 추정하였다. 그러나 매트릭스 내에서 탐침입자의 확산운동은 모든 측정농도에서 단일모드로 관찰되었고, 용액상 및 용매상에서의 확산계수의 비인 D/Do를 $C[{\eta}]$로 도시할 때 전체 농도 범위에서 분자량 의존성은 전혀 나타나지 않았으나 신장지수함수의 적용 한계는 C$[{\eta}]$ >2.5인 것으로 관찰되었다.

• Bulletin of the Korean Chemical Society
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• 제8권4호
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• pp.318-324
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• 1987

Experimental results for viscous flow of poly (${\gamma}$ -methyl L-glutamate) solutions have been published elsewhere. The data of $[{\eta}]^f / [{\eta}]^0$ are expressed by the following equation, $\frac{[{\eta}^f]}{[{\eta}^{\circ}]}=1-\frac{A}{\eta^\circ}{1-\frac{sin^{-1}[{\beta}_2(f/{\eta}_0)\;{e}xp\;(-c_2f^2/{\eta}_0^2kT)]}{{\beta}_2f/{\eta}_0}$ (A1) where $[{\eta}]^f\; and\; [{\eta} ]^0$ are the intrinsic viscosity at shear stress f and zero, respectively, $ A{\equiv}lim\limits_{C{\rightarrow}0}[(1/C)(X_2/{\alpha}_2)({\beta}_2/{\eta}_0)],{\eta}_0$ viscosity of the solvent, ${\beta}_2$ is the relaxation time of flow unit 2, $c_2$ is a constant related to the elasticity of flow unit 2. The theoretical derivation of Eq.(A1) is given in the text. The experimental curves of $[{\eta}]^f / [{\eta}]^0$ vs. log f are compared with the theoretical curves calculated from Eq.(A1) with good results. Eq.(A1) is also applied to non-biopolymeric solutions, and it was found that in the latter case $c_2 = 0.$ The reason for this is explained in the text. The problems related to non-Newtonian flows are discussed.

• Preventive Nutrition and Food Science
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• 제19권3호
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• pp.242-245
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• 2014

The flow behaviors of three thickened fruit juices (orange, apple, and grape juice) prepared with a commercial instant xanthan gum (XG)-based thickener that is marketed in Korea were investigated at different thickener concentrations (1.0%, 1.5%, 2.0%, 2.5%, 3.0%, and 3.5%) and setting times (5 and 30 min) using a rheometer and a line-spread measurement method. The flow distance values measured by the line-spread test (LST) were compared with the apparent viscosity (${\eta}_{a,50}$) values measured with a sophisticated computer-controlled rheometer. The ${\eta}_{a,50}$ values of the juices increased as thickener concentration increased, whereas their flow distances decreased. The ${\eta}_{a,50}$ values at the 30-min setting time were much higher than those at the 5-min setting time, indicating that the setting time before serving or consuming thickened juices can affect viscosity values. Plots comparing ${\eta}_{a,50}$ values to LST flow distances revealed strong exponential relationships between the two measures ($R^2$=0.989 and $R^2$=0.987 for the 5- and 30-min setting times, respectively). These results indicate that the LST can be a suitable instrument for evaluating the viscosity of thickened fruit juices prepared with different XG-based thickener concentrations and setting times for the dysphagia diet.

• Bulletin of the Korean Chemical Society
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• 제32권11호
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• pp.3909-3913
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• 2011

In this paper we have carried out molecular dynamics simulations (MD) for model systems of liquid n-alkane oligomers ($C_{12}{\sim}C_{80}$) at high temperatures (~2300 K) in a canonical ensemble to calculate viscosity ${\eta}$, self-diffusion constants D, and monomeric friction constant ${\zeta}$. We found that the long chains of these n-alkanes at high temperatures show an abnormality in density and in monomeric friction constant. The behavior of both activation energies, $E_{\eta}$ and $E_D$, and the mass and temperature dependence of ${\eta}$, D, and ${\zeta}$ are discussed.

• 한국식품과학회지
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• 제31권3호
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• pp.870-874
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• 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.

• Bulletin of the Korean Chemical Society
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• 제8권4호
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• pp.332-335
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• 1987

This paper is a continuation of our previous $paper,^1$ and deals with Eq.(1) (see the text), which was theoretically derived in the $paper,^1$$ [{\eta}]^f\; and\; [{\eta}]^0$ is the intrinsic viscosity at stress f and f = O, respectively. Equation (1) predicts how $[{{\eta}}]^f / [{\eta}]^0$ changes with stress f, relaxation time ${\beta}_2$ of flow unit 2 and a constant $c_2$ related with the elasticity of molecular spring of flow unit 2. In this paper, Eq.(1) is applied to a biopolymer, e.g., poly (${\gamma}$-benzyl L-glutamate), and nonbiopolymers, e.g., polyisobutylene, polystyrene, polydimethylsiloxane and cellulose triacetate. It was found that the $c_2$ factor is zero for non-biopolymers while $c_2{\neq}0$ for biopolymers as found $previously.^1$ Because of the non-Newtonian nature of the solutions, the ratio $[{{\eta}}]^f / [{\eta}]^0$ drops from its unity with increasing f. We found that the smaller the ${\beta}_2,$ the larger the $f_c$ at which the viscosity ratio drops from the unity, vice versa.

• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1590-1598
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• 2003

In this paper we have presented the results for viscosity and self-diffusion constants of model systems for four liquid n-alkanes ($C_{12}, C_{20}, C_{32}, and C_{44}$) in a canonical ensemble at several temperatures using molecular dynamics (MD) simulations. The small chains of these n-alkanes are clearly $<{R_{ee}}^2>/6<{R_g}^2>>1$, which leads to the conclusion that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime. Calculated viscosity ${\eta}$ and self-diffusion constants D are comparable with experimental results and the temperature dependence of both ${\eta}$ and D is suitably described by the Arrhenius plot. The behavior of both activation energies, $E_{\eta}$ and $E_D$, with increasing chain length indicates that the activation energies approach asymptotic values as n increases to the higher value, which is experimentally observed. Two calculated monomeric friction constants ${\zeta}$ and ${\zeta}_D$ give a correct qualitative trend: decrease with increasing temperature and increase with increasing chain length n. Comparison of the time auto-correlation functions of the end-to-end vector calculated from the Rouse model for n-dodecane ($C_{12}$) at 273 K and for n-tetratetracontane ($C_{44}$) at 473 K with those extracted directly from our MD simulations confirms that the short chain n-alkanes considered in this study are far away from the Rouse regime.

• Korea-Australia Rheology Journal
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• 제21권4호
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• pp.225-233
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• 2009

In various attempts to relate the behaviour of highly-elastic liquids in complex flows to their rheometrical behaviour, obvious candidates for study have been the variation of shear viscosity with shear rate, the two normal stress differences $N_1$ and $N_2$, especially $N_1$, and the extensional viscosity $\eta_E$. In this paper, we shall be mainly interested in 'constant-viscosity' Boger fluids, and, accordingly, we shall limit attention to $N_1$ and $\eta_E$. We shall concentrate on two important flows - axisymmetric contraction flow and "splashing" (particularly that which arises when a liquid drop falls onto the tree surface of the same liquid). Modern numerical techniques are employed to provide the theoretical predictions. It is shown that the two obvious manifestations of viscoelastic rheometrical behaviour can sometimes be opposing influences in determining flow characteristics. Specifically, in an axisymmetric contraction flow, high $\eta_E$ can retard the flow, whereas high $N_1$ can have the opposite effect. In the splashing experiment, high $\eta_E$ can certainly reduce the height of the so-called Worthington jet, thus confirming some early suggestions, but, again, other rheometrical influences can also have a role to play and the overall picture may not be as clear as it was once envisaged.

• 대한화학회지
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• 제8권1호
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• pp.9-14
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• 1964

전해질용액의 점도가 농도의 양수임은 기지의 사실이나 전농도에 걸쳐 잘 맞는 관계식은 아직 발견되지 않았다. 표면장력 역시 이러한 관계가 있으나 완전한 식은 없으며 이들은 모두 용액내의 이온의 상태에 기인하므로 표면장력과 덤도간에도 일정한 관계가 있을 것으로 생각되는 바이다. 순수한 물질에 대한 관계식은 Silverman1)이 Batchinski식 과 MacLeod 식에서 ${\gamma}^{\frac{1}{4}}=\;A/{\eta}$ + B 식을 유도하여 실험오차 범위안에서 일치된다고 했으나 아직 $Jones^{(4)}$들이 측정한 몇가지 염을 제외하고는 거의 모든 염용액의 점도나 표면장력의 정밀한 값은 측정되지 않았음으로 우선 여기서는 몇가기 염용액의 점도를 측정하였고 또 점도계수와 농도관계를 고찰하였다.