• Food Science and Biotechnology
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• v.14 no.1
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• pp.11-15
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• 2005

Dynamic shear moduli of isolated soy protein solutions upon heating were measured to monitor gelation. Onsets of gelation coincide with onset temperatures of denaturation in glycinin and ${\beta}$-conglycinin solutions, whereas in isolated soy proteins, onset of gelation was above denaturation temperature of ${\beta}$-conglycinin with storage modulus increasing in two steps. The first increase in storage modulus of isolated soy proteins occurred at about $78.5^{\circ}C$, while the second increase started at about $93^{\circ}C$. Gel properties of soy protein gels having different proportions of glycinin and ${\beta}$-conglycinin were measured by compression-decompression test. ${\beta}$-conglycinin was responsible for gel elasticity. Glycinin significantly increased hardness, toughness, and fracturability of gels at high heating temperature near $100^{\circ}C$. Results reveal texture of soy protein gels can be controlled by regulating ratio of glycinin to ${\beta}$-conglycinin and heating temperature.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.210-215
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• 2002

MR(Magnetorheogical) fluid composed of fine iron powders dispersed in silicon oil is utilized to many smart structures and devices because of its significant rheological property change by the application of an external magnetic field. When we deal with the shock wave attenuation of warship structures, we should be able to characterize the high frequency behavior of MR fluids. So far, however, many efforts have been focused on the material characterization of MR fluids at low frequencies below 100Hz. In this paper, the MR fluid property characterization at high frequency region is performed. An experimental setup based on wave transmission technique is made and the storage modulus as well as the loss modulus of MR fluids are found from the measured data of speed sound and attenuation. Details of the experiment are addressed and the obtained storage and loss moduli are addressed at $50kHz{\sim}100kHz$.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.7
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• pp.1046-1052
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• 2003

Viscoelastic behavior of oxidized starch gel, modified with sodium hypochlorite (NaOCl) and the adding effects of protein in oxidized starch gel was studied by dynamic viscoelastic measurement. The storage modulus(G′) of starch gel increased with the increase of starch concentration. They showed higher value when starch suspension was treated to 95$^{\circ}C$ rather than 85$^{\circ}C$. Consistency of starch gel was decreased over 1.0% active Cl/g starch when heated to 95$^{\circ}C$, which means that the swelling of starch granules increased with concentration of NaOCl and showed more sensitive against shear. As the extent of oxidation increased, starch granules were easily destroyed. Therefore, it is hard to separate between compartment of leached-out amylose and that of amylopectin, which means that the ability of gel formation was reduced. When oxidized starches were gelatinized in presence of soy protein and sodium caseinate, it was found that G′ decreased, and frequency dependence of G′ and G" increased with the increased degree of oxidation in starch. The reduce of starch-protein interaction was thought to be through the dissociation of the branched amylopectin, which playa leading role in protein interaction, with the oxidation of starch.

• Korea-Australia Rheology Journal
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• v.18 no.2
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• pp.67-81
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• 2006

Using a strain-controlled rheometer, the dynamic viscoelastic properties of aqueous xanthan gum solutions with different concentrations were measured over a wide range of strain amplitudes and then the linear viscoelastic behavior in small amplitude oscillatory shear flow fields was investigated over a broad range of angular frequencies. In this article, both the strain amplitude and concentration dependencies of dynamic viscoelastic behavior were reported at full length from the experimental data obtained from strain-sweep tests. In addition, the linear viscoelastic behavior was explained in detail and the effects of angular frequency and concentration on this behavior were discussed using the well-known power-law type equations. Finally, a fractional derivative model originally developed by Ma and Barbosa-Canovas (1996) was employed to make a quantitative description of a linear viscoelastic behavior and then the applicability of this model was examined with a brief comment on its limitations. Main findings obtained from this study can be summarized as follows: (1) At strain amplitude range larger than 10%, the storage modulus shows a nonlinear strain-thinning behavior, indicating a decrease in storage modulus as an increase in strain amplitude. (2) At strain amplitude range larger than 80%, the loss modulus exhibits an exceptional nonlinear strain-overshoot behavior, indicating that the loss modulus is first increased up to a certain strain amplitude(${\gamma}_0{\approx}150%$) beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (3) At sufficiently large strain amplitude range (${\gamma}_0>200%$), a viscous behavior becomes superior to an elastic behavior. (4) An ability to flow without fracture at large strain amplitudes is one of the most important differences between typical strong gel systems and concentrated xanthan gum solutions. (5) The linear viscoelastic behavior of concentrated xanthan gum solutions is dominated by an elastic nature rather than a viscous nature and a gel-like structure is present in these systems. (6) As the polymer concentration is increased, xanthan gum solutions become more elastic and can be characterized by a slower relaxation mechanism. (7) Concentrated xanthan gum solutions do not form a chemically cross-linked stable (strong) gel but exhibit a weak gel-like behavior. (8) A fractional derivative model may be an attractive means for predicting a linear viscoelastic behavior of concentrated xanthan gum solutions but classified as a semi-empirical relationship because there exists no real physical meaning for the model parameters.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1416-1425
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• 2002

In this study, the effects of combined environmental factors on mechanical and thermal analysis properties of graphite/epoxy composites were evaluated by the use of an accelerated aging test. Environmental factors such as temperature, moisture. and ultraviolet were considered. A xenon-arc lamp was utilized for ultraviolet light. and exposure times of up to 3000 hours were applied. Several types of specimens - tensile. bending, and shear specimens those are transverse to the fiber direction, and bending specimens those are parallel to the tiber direction - were used to investigate the effects of environmental factors on mechanical properties of the composites. Also, glass transition temperature, storage shear modulus, loss shear modulus, and tan ${\delta}$ were measured as a function of exposure times through a dynamic mechanical analyzer. In addition. a suitable testing method for determining the effect of environmental factors on mechanical properties is suggested by comparing the results from using two different types of strain measuring sensors. Finally, composite surfaces exposed to environmental factors were examined using a scanning electron microscope.

• Journal of the Korean Society for Railway
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• v.8 no.2
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• pp.188-194
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• 2005

Aging characteristics of glass fabric/phenolic composites for tilting train subjected to combined environmental aging factors were investigated. A 2.5KW accelerated aging tester with a xenon-arc lamp was used to provide environmental aging factors such as temperature, moisture, and ultraviolet. A series of aging tests were conducted up to 3000 hours and several types of specimens were prepared along the warp direction and the fill direction. Mechanical degradations for tensile, flexural, and shear properties were evaluated as a function of exposure times through a material testing system. Thermal analysis properties such as storage shear modulus, loss shear modulus, and tan 3 were measured through a dynamic mechanical analyzer. Finally exposed surfaces of the composites were examined using a scanning electron microscope. According to the experimental results, mechanical properties and thermal analysis properties of glass fabric/phenolic composites were found to be slightly degraded as a function of exposure times due to combined environmental effects.

• Food Science and Biotechnology
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• v.15 no.4
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• pp.589-594
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• 2006

The effect of five commercial gums (carboxylmethylcellulose, CMC; guar gum, GG; hydroxypropylmethyl-cellulose, HPMC; locust bean gum, LBG; and xanthan gum) at a concentration of 0.25% on the rheological properties of rice flour (RF) dispersions was investigated in steady and dynamic shear. The steady shear rheological properties showed that RF gum mixture dispersions (5%, w/w) at $25^{\circ}C$ had high shear-thinning flow behavior (n=0.20-0.31) exhibiting a yield stress. Magnitudes of consistency index (K), apparent viscosity (${\eta}_{a,100}$), and Casson yield stress (${\sigma}_{oc}$) of RF-gum mixtures were much higher than those of RF dispersion with no added gum (control). Activation energy values (6.67-10.8 kJ/mole) of RF-gum mixtures within the temperature range of $25-70^{\circ}C$ were lower than that (11.9 kJ/mole) of the control. Dynamic rheological data of log (G', G") versus log frequency (${\omega}$) of RF-gum mixtures had positive slopes (0.15-0.37) with G' greater than G" over most of the frequency range (0.63-63 rad/sec), demonstrating a frequency dependency. Tan ${\delta}$ (G"/G') values of RF-gum mixtures, except for xanthan gum, were much higher than that of the control.

• Elastomers and Composites
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• v.48 no.1
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• pp.18-23
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• 2013

Nylon 12 elastomer was slightly crosslinked in molten state by the addition of small amount of dicumyl peroxide (DCP) as a crosslink agent and triallycyanuate (TAC) as a co-agent during melt compounding at $160^{\circ}C$ in an internal mixer. The effect of the peroxide crosslinking on mechanical, dynamic mechanical and rheological properties of the nylon 12 elastomer was investigated by means of tensile testing, dynamic mechanical analysis (DMA) and small amplitude oscillating rheometer, respectively. With modification, there is an improvement in tensile modulus and Young's modulus with decease in elongation at break. DMA results for peroxide modified nylon 12 elastomers demonstrated that the glass transiaiton temperature of PTMG segment shifted to higher temperature and the storage modulus remained constant above the melting temperature of nylon 12 segments. Melt rheological studies revealed that the peroxide modified nylon 12 elastomer exhibited a more solid like behavior and stronger shear thinning behavior compared to neat nylon 12 elastomer, which was more prominent at higher TAC content in the polymer matrix. The peroxide modified nylon 12 elastomer exhibited good elastic recoverability and improved mechanical properties without sacrificing melt processibilty, and especially the service temperature range increased as compared to neat nylon 12 elastomer.

• Korea-Australia Rheology Journal
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• v.19 no.1
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• pp.35-42
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• 2007

The effects of particle size distribution on the magnetorheological response of inverse ferrofluids was investigated using controlled mixtures of two monodisperse non-magnetisable powders of sizes $4.6\;{\mu}m\;and\;80{\mu}m$ at constant volume fraction of 30%, subjected to large amplitude oscillatory shear flow. In the linear viscoelastic regime (pre-yield region), it was found that the storage and loss moduli were dependent on the particle size as well as the proportion of small particles, with the highest storage modulus occurring for the monodisperse small particles. In the nonlinear regime (post yield region), Fourier analysis was used to compare the behaviour of the $1^{st}\;and\;3^{rd}$ harmonics ($I_{1}\;and\;I_{3}\;respectively$) as well as the fundamental phase angle as functions of the applied strain amplitude. The ratio of $I_{3}/I_{1}$ was found to become more pronounced with decreasing particle size as well as with increasing proportion of small particles in the bidisperse mixtures. Furthermore, the phase angle was able to clearly show the transition from solid-like to viscous behaviour. The results suggested that the nonlinear response of a bidisperse IFF is dependent on particle size as well as the proportion of small particles in the system.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.22 no.2
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• pp.167-173
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• 1996

The stability of gel structured emulsion and the effect of polyols on it have been studied by rheological property and interfacial tension. In this paper, three types of gel structured emulsions were prepared by using three polyols respectively(glycerine for sample 1, 1.3 BG for sample 2, PG for sample 3). And both complex modulus($G^*$) and loss angle[$\delta$ = tan-1(G"/G')] of samples were investigated against oscillating shear stress and frequency($\omega$). The results show sample 1 is most highly consistent with oscillating shear stress. And the results were compared with those of accelerated tests concerning storage stability of gel structured emulsion. To correlate consistency of rheological property with storage stability, interfacial tension from which adsorption efficiency of surfactant(Octyldodecyl Ether) could be known was measured. Sample 1 showed the largest value of [$d{\gamma}/dIn_{Cconc. of surfactant}$] in Gibbs equation. In summary, the prediction of stability could be correctly made by the consistency of rheological property(G*,$\gamma$) of gel structured emulsion against oscillating shear stress and it could be supported by measuring interfacial tension. And polyol affected the value of [$d{\gamma}/dIn_{Cconc. of surfactant}$], consequently affected the stability.lity.