• 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 Society of Cosmetic Scientists of Korea
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• v.37 no.1
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• pp.37-42
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• 2011

The rheological properties of the aqueous solution of scleroglucan industrially produced by Sclerotium rolfsii at concentrations ranging from 0.1 % to 2 % (w/w) were determined by using brookfield viscometer and rheometer. Gel matrices of scleroglucans were stable over a wide range of pH and ionic strength in the aqueous medium. In the oil dispersion with phytosqualane in oil phase and three kinds of thickening agent in aqueous phase, scleroglucan showed the highest dispersion properties. The synergistic effect between scleroglucan and locust bean gum was also examined. The highest viscosity was obtained for the solution mixture at scleroglucan/locust bean gum weight ratio of 5 : 5. The results of this study suggest the potential of scleroglucan as thickner for a wide variety of cosmetic formulations.

• YAKHAK HOEJI
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• v.32 no.1
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• pp.86-94
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• 1988

Some rheological properties of subfractions for dextran in the molecular weights range from $3{\times}10^4$ to $2{\times}10^6$ was investigated at room temperature. The dependence of the viscosity on concentration, shear rate, pH & ionic strength, temperature and solvent effect was observed. From the experimental data the Mark-Houwink viscosity equation in water at $25^{\circ}C$ was determined for samples having the molecular weight ranging from $3{\times}10^4$ to $2{\times}10^6$ as$[{\eta}]=3.1{\times}10^{-3}\;Mw^{0.39}(in\;dl/g)$. The intrinsic stiffness of the dextran backbone was estimated by evaluating the 'characteristic ratio' $C_{\infty}$, which is below the 0.082. In the concentrated region, the viscosity was decreased with increasing shear rate and was exponentially decreased with raising temperature, the viscosity showed the maximum value at neutral condition. From the experimental data, it was concluded that dextran chain, linked by the ${\alpha}-1$, 6-glucosidic linkage, behaves like a flexible random coil chain in aqueous solution, dextran solutions were pseudoplastic power law fluids among the empirical models of non-Newtonian behavior. Urea was an active reagent which increases the viscosity and swells dextran while pyrididine and glycerol were inactive reagents. Also, it could be estimated that the formation of gel structure is promote to the neutral state, the molecular weight larger than $2{\times}10^5$, when electrolytic concentration is IN and Ureas is use to solvent.

• Macromolecular Research
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• v.16 no.3
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• pp.218-223
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• 2008

In order to obtain crosslinked poly(butylene succinate) (PBS) foams with a closed-cell structure, a commercial-grade PBS was first modified in the melt using two different branching agents to increase the melt viscosity. The rheological properties of the branched and crosslinked PBS were examined by varying the amount of the branching agents. The complex viscosity of the crosslinked PBS increased with increasing amount of the branching agent. However, it decreased with increasing frequency. When 2 phr of the branching agent was added to PBS, the storage modulus (G') was higher than the loss modulus (G") throughout the entire frequency range, showing that the addition of a branching agent increases the melt viscosity and elasticity of PBS effectively. Closed-cell PBS foams were prepared by mixing the chemical blowing agent with the crosslinked PBS. The effect of the foaming conditions such as temperature and time, and the amount of the crosslinking agent on the structure of the expanded PBS foams were also investigated.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.2
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• pp.199-204
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• 2014

An experimental investigation on the rheological behavior of gelled hydrogen peroxide at different ambient temperature (283.15, 293.15 and 303.15 K) was carried out in this study. The gel propellant was rheologically characterized using a rheometer, in the shear rate ranges of 1 to $20s^{-1}$, and 1 to $1000s^{-1}$. Hydrogen peroxide gel was found to be thixotropic in nature. The apparent viscosity value with some yield stress (in-case of shear rate 1 to $20s^{-1}$) drastically fell with the shear rate. In the case of the shear rate range of 1 to $20s^{-1}$, the apparent viscosity and yield stress of gel were significantly reduced at higher ambient temperatures. In the case of the shear rate range of 1 to $1000s^{-1}$, no significant effect of varying the ambient temperature on the gel apparent viscosity was observed. The up and down shear rate curves for hydrogen peroxide gel formed a hysteresis loop that showed no significant change with variation in temperature for both the 1 to $20s^{-1}$ and the 1 to $1000s^{-1}$ shear rate ranges. No significant change in the thixotropic index of gel was observed for different ambient temperatures, for both low and high shear rates. The gel in the 1 to $20s^{-1}$ shear rate range did not lead to a complete breakdown of gel structure, in comparison to that in the 1 to $1000s^{-1}$ shear rate range.

• Korean journal of food and cookery science
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• v.8 no.2
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• pp.155-163
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• 1992

Rhamsan gum produced by Alcaligenes was rheologically characterized, and compared to that of xanthan gum. The rheological properties were derermined from the change in the value of intrinsic viscosity with pH and salt concentration. at the range of pH 2~11 and salt concentration of 0~1.0 M KCl, the intrinsic viscosties of rhanisan gum were in the range of 8.2 to 36.2 dl/g and those of xanthan gum 8.19 to 44 dl/g. In the absence of salt, the intrinsic viscosity of rhamsan gum and Xanthan gum increased as the pH of solution increased up to neutral pH, and then decreased at alkaline pH. The intrinisc viscosities of rhamsan and anthan gum were not affec6ted by the increment of salt concentration. the chain stiffness paramenter for the rhamsan gum was 0.016. The overlap paramoeters of rhamsan and xanthan gum were 0.025 and 0.022 g/dl, respectively. rhamsan and xanthan gum were shear rate dependent or pseudoplastic. The yield stress of rhamsan gum increased slightly, but the shear index decreased as the concentration increased. The apparent viscosityes of rhamsan and xanthan gum decreased as the temperature increased. The salt effect of divalent cations (calcium, magnesium) was lower than monovalent cations (sodium, potassium).

• Biomaterials Research
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• v.22 no.4
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• pp.249-258
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• 2018

Background: Mucoadhesive polymers, which may increase the contact time between the polymer and the tissue, have been widely investigated for pharmaceutical formulations. In this study, we developed a new polysaccharide-based mucoadhesive polymer with thermogelling properties. Methods: Hexanoyl glycol chitosan (HGC), a new thermogelling polymer, was synthesized by the chemical modification of glycol chitosan using hexanoic anhydride. The HGC was further modified to include thiol groups to improve the mucoadhesive property of thermogelling HGC. The degree of thiolation of the thiolated HGCs (SH-HGCs) was controlled in the range of 5-10% by adjusting the feed molar ratio. The structure of the chemically modified polymers was characterized by $^1H$ NMR and ATR-FTIR. The sol-gel transition, mucoadhesiveness, and biocompatibility of the polymers were determined by a tube inverting method, rheological measurements, and in vitro cytotoxicity tests, respectively. Results: The aqueous solution (4 wt%) of HGC with approximately 33% substitution showed a sol-gel transition temperature of approximately $41^{\circ}C$. SH-HGCs demonstrated lower sol-gel transition temperatures ($34{\pm}1$ and $31{\pm}1^{\circ}C$) compared to that of HGC due to the introduction of thiol groups. Rheological studies of aqueous mixture solutions of SH-HGCs and mucin showed that SH-HGCs had stronger mucoadhesiveness than HGC due to the interaction between the thiol groups of SH-HGCs and mucin. Additionally, we confirmed that the thermogelling properties might improve the mucoadhesive force of polymers. Several in vitro cytotoxicity tests showed that SH-HGCs showed little toxicity at concentrations of 0.1-1.0 wt%, indicating good biocompatibility of the polymers. Conclusions: The resultant thiolated hexanoyl glycol chitosans may play a crucial role in mucoadhesive applications in biomedical areas.

• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.262-271
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• 2023

For electrode stability and the electrochemical performance of the Li-ion cell, it is essential that the active ingredients and unique additives in the polymer binder be well dispersed with the solvent-based slurry. The efficient procedure used to create the slurry affects the rheological characteristics of the electrode slurry. When successively adding different steps of Nmethyl-2-pyrrolidone (NMP) solvent to the cathode composition, it is evenly disseminated. The electrochemical performance of the Li-ion cells and the electrodes made with slurry formed by single step and multiple steps of addition of NMP solvent are examined. To preform rheological properties of cathode electrode slurry on Ni-rich Lithium Nickel-Cobalt-Aluminum Oxide (LiNi_0.80Co_0.15Al_0.05) (NCA). Also, we investigate different step addition of electrode formation and mechanical strength characterization like peel strength. According to the EIS study, a multi-step electrode slurry has lower internal resistance than a single-step electrode slurry, which results in better electrical characteristics and efficiency. Further, microstructure of electrodes is obtained electrochemical performance in the 18650 cylindrical cells with targeted capacity of 1.5 Ah. The slurry of electrodes prepared by single step and multiple steps of addition of NMP solvent and its effect on the fabrication of 1.5 Ah cells. A three-step solvent addition on slurry has been found to be a lower internal resistance than a single-step electrode slurry as confirmed by the EIS analysis, yielding improved electrical properties and efficiency.

• Journal of the Mineralogical Society of Korea
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• v.16 no.1
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• pp.33-47
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• 2003

Various applied-mineralogical characterization including measurements of surface area, size distribution, swelling index, and viscosity were done for some domestic bentonites in order to decipher the rheological properties and their controlling factors. The bentonites, which are Ca-type and relatively low-grade (rnontmorillonite contents: 30 ∼ 75 wt%), occur mostly as subhedral lamellas with the size range of 2 ∼ 4 $\mu\textrm{m}$. The size distribution of mineral fractions in bentonite suspension is dominant in the range of 10 ∼ 100 $\mu\textrm{m}$, and though rather complicated, exhibits roughly bimodal patterns. The feature is more conspicuous in the case of zeolitic bentonite. The bentonites have surface areas ranging 269 ∼ 735 $\m^2$/g, which are measured by EGME adsorption method. The EGME surface areas are nearly proportional to the rnontmorillonite contents, moisture contents, or total CEC. In the surface area measurements, zeolitic bentonites have slightly higher values than those zeolite- free types. The measured swelling index and viscosity of domestic bentonites are comparatively low in values. The swelling values of bentonites were measured to be 250∼500% at maximum by progressively mixing amounts of 2 ∼ 5 wt% Na$_2$CO$_3$, which varies depending on the contents of rnontmorillonite and other impurities, especially zeolite. Much amount of sodium carbonate is required for optimum swelling property of zeolitic bentonited which has usually strong Na- exchanged capacity. The bentonites, which are comparatively feldspar-rich and low in size and crystallinity, tend to be higher in viscosity values. Tn addition, the viscosity is largely higher in case of the bentonites with higher pH in suspension. However, the rheological properties of bentonites such as swelling index and viscosity do not show any obvious relationships with rnontmorillonite contents and mean particle size in suspension. In contrast, roughly speaking, the swelling index of bentonites is reversely proportional to the values of surface area which can be regarded as a collective physico-chemical parameter encompassing all the effects caused by mineral composition, surface charge, particle size, morphological farm, and etc. in bentonites. Thus, the rheological properties in bentonite suspension appear to be rather complicated characteristics which mainly depend on the flocculation of clay particles and the mode of particle association, i.e. quasicrystals, controlled by surface charge, morphology, size, and texture of rnon-tmorillonite, and which partly affected by the finer impurities such as zeolite.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.52-55
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• 2003

Poly (ethylene 2, 6-naphthalate) (PEN) has been used for a high performance engineering plastics such as fiber, film, and packaging, because of excellent physical properties and outstanding gas barrier characteristics [1-2]. However, the application of PEN is limited because PEN exhibits a relatively high melt viscosity. Recently, many researches for organic/inorganic composites by applying nano-particles to the polymer matrix have been carried out [3], and the nano-particles exhibited greatly improved mechanical and rheological properties [4]. (omitted)