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RISS 인기검색어
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- 저자 : 배준웅(Jun Woong Bae) (검색결과 2 건)
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정상전단유동의 급개시에 따른 폴리에틸렌옥사이드 수용액의 응력성장거동
배준웅,이지석,송기원,Bae, Jun-Woong,Lee, Ji-Seok,Song, Ki-Won 한국섬유공학회 2013 한국섬유공학회지 Vol.50 No.5
The objective of this study is to systematically elucidate the transient rheological behavior of viscoelastic polymer solutions at start-up of steady shear flow. Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the stress overshoot behavior of concentrated aqueous poly(ethylene oxide) [PEO] solutions has been thoroughly investigated with applying a number of shear rates to these polymer solutions. In this article, the typical stress growth behavior of aqueous PEO solutions was firstly presented on the basis of experimentally obtained data and nextly the effects of shear rate, molecular weight, and concentration on this behavior were discussed in depth. In order to theoretically predict the stress growth behavior, the Wagner constitutive equation (a time-strain separable constitutive equation) and the Bird-Leider model were employed and the applicability of these models was examined in detail. The main findings obtained from this study can be summarized as follows: (1) At the inception of low shear rates, the stress overshoot behavior is not observed but the shear stress progressively increases with time until the steady state stress value is reached. As the shear rate is increased, however, aqueous PEO solutions exhibit a pronounced stress overshoot followed by a stress decay to reach the steady state flow condition. (2) The maximum shear stress increases linearly with an increase in shear rate in a double logarithmic scale and becomes larger with an increase in concentration. (3) The time at which the maximum shear stress occurs, $t_{max}$, shows a linear relationship with the inverse of shear rate in a double logarithmic scale, regardless of molecular weight and concentration. (4) When the Wagner constitutive equation is used, the Wagner damping function exhibits superior performance to the Soskey-Winter damping function in predicting the transient stress growth behavior of aqueous PEO solutions. (5) The Bird-Leider empirical model can be successfully used for predicting the transient stress growth behavior of aqueous PEO solutions. This model is especially effective for expressing the maximum shear stress as well as the time at which this maximum stress is observed.
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송기원(Ki Won Song),배준웅(Jun Woong Bae),장갑식(Gap Shik Chang),노동현(Dong Hyun Noh),박영훈(Yung Hoon Park),이치호(Chi Ho Lee) 한국약제학회 1999 Journal of Pharmaceutical Investigation Vol.29 No.4
Using a Rheometrics Fluids Spectrometer (RFS II), the dynamic viscoelastic properties of aqueous poly(ethylene oxide) (PEO) solutions in small amplitude oscillatory shear flow fields have been measured over a wide range of angular frequencies. The angular frequency dependence of the storage and loss moduli at various molecular weights and concentrations was reported in detail, and the result was interpreted using the concept of a Deborah number De. In addition, the experimentally determined critical angular frequency at which the storage and loss moduli become equivalent was compared with the calculated characteristic time (or its inverse value), and their physical significance in analyzing the dynamic viscoelastic behavior was discussed. Finally, the relationship between steady shear flow and dynamic viscoelstic properties was examined by evaluating the applicability of some proposed models that describe the correlations between steady flow viscosity and dynamic viscosity, dynamic fluidity, and complex viscosity. Main results obtained from this study can be summarized as follows : (1) At lower angular frequencies where De<1, the loss modulus is larger than the storage modulus. However, such a relation between the two moduli is reversed at higher angular frequencies where De>1, indicating that the elastic behavior becomes dominant to the viscous behavior at frequency range higher than a critical angular-frequency. (2) A critical angular frequency is decreased as an increase in concentration and/or molecular weight. Both the viscous and elastic properties show a stronger dependence on the molecular weight than on the concentration. (3) A characteristic time is increased with increasing concentration and/or molecular weight. The power-law relationship holds between the inverse value of a characteristic time and a critical angular frequency. (4) Among the previously proposed models, the Cox-Merz rule implying the equivalence between the steady flow viscosity and the magnitude of the complex viscosity has the best validity. The Osaki relation can be regarded to some extent as a suitable model. However, the DeWitt, Pao and Huseby-Blyler models are not applicable to describe the correlations between steady shear flow and dynamic viscoelastic properties.
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