• Journal of the Korean Ceramic Society
• /
• v.42 no.11 s.282
• /
• pp.737-742
• /
• 2005

Rheological properties of ordinary portland cement (OPC) containing metakaoline (MK), granulated blast furnace slag (GBS) and polycarboxylate type superplasticizer (PCA) were investigated using a mini-slump test, sedimentation test and viscometer. Fluidity of cement pastes containing MK (OPC-MK, OPC-MK-GBS systems) with PCA were higher than those of the cement pastes without MK(OPC, OPC-GBS systems). Colloid suspensions with $0.1\%$ PCA were changed from stable sedimentation behaviors to flocculation behaviors in the OPC-MK, OPC-GBS and OPC-MK-GBS systems. The colloid suspensions showed stable sedimentation behaviors with PCA greater than $0.2\%$. The OPC system showed shear thinning behavior. However, the other systems showed weak shear thinning behaviors with PCA. Rheological properties of cement pastes were improved when MK and GBS were contained together. The rheological properties of OPC-MK, OPC-GBS and OPC-MK-GBS systems were improved by PCA added greater than $0.2\%$.

• Elastomers and Composites
• /
• v.54 no.4
• /
• pp.335-344
• /
• 2019

In this work, styrene butadiene rubber (SBR) and styrene butadiene styrene (SBS) were used to modify asphalt, resulting in SBR- and SBS-modified asphalt, respectively. The two modified asphalts were emulsified with a nonionic emulsifier (Span 60) and cationic emulsifiers (ID, DDA) and their phase stabilization was investigated via particle size, Zeta potential, and flow behavior analysis. With increasing amount of the mixed emulsifier, the particle size decreased, leading to an increase in viscosity. The shear thinning behaviors and Zeta potential values ranging from 35-65 mV were determined and remained considerably stable. In addition, the adhesion strength and compression strength of the SBR-and SBS-modified asphalt emulsion were evaluated via surface free energy examination. The remarkable adhesion and compression strengths were estimated when 5 phr ID and 6 phr DDA were added to the emulsified asphalt modified with SBR and SBS. Therefore ID and DDA, the two cationic surfactants, played significant roles in improving the dispersion and interfacial adhesion strength, resulting in the improved adhesion and compression strength of the emulsified asphalts modified with SBR and SBS.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.4
• /
• pp.1988-1992
• /
• 2011

Polypropylene (PP)-SEBS/silicate composites with PP content of 35, 40, and 45wt% were fabricated by melt compounding at $200^{\circ}C$, using lab scale Brabender mixer. The content of silicate was fixed at 5wt%. The thermal properties of the PP-SEBS/silicate composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). The melting temperature of PP-SEBS compound decreased up to $141^{\circ}C$ with SEBS content. TGA result indicates an increase in degradation temperature when the silicate was added in the PP-SEBS compound. The rheological properties of the compounds were measured by dynamic Rheometer. PP-SEBS/silicate composite indicates higher shear thinning and elastic property than PP-SEBS compound. Van Gurp-Palmen analysis was applied in order to certify an increase in elasticity.

• Korean Journal of Food Science and Technology
• /
• v.32 no.6
• /
• pp.1313-1318
• /
• 2000

총고형분 함량$(TS:\;50{\sim}57%)$을 달리하여 숙성시킨 고추장의 유동특성, 정적 및 동적점탄특성을 관찰하였다. 고추장의 TS가 증가함에 따라서 점조도 지수(K)와 겉보기 점도$({\eta}_{a.5})$는 증가하였으며 유동성 지수(n)는 1보다 훨씬 낮은 0.24-0.31의 범위를 나타내어 고추장은 shear-thinning 성질을 보여주었다. 고추장의 항복응력 측정에서는 고추장의 TS가 증가함에 따라 Casson 항복응력$({\sigma}_{oc})$은 증가하는 경향을 나타내었으며, 또한 고추장의 액상 매개체인 serum 점도$({\eta}_{se})$는 고추장의 TS와 매우 좋은 상관관계$(R^2=0.97)$를 나타내었다. 고추장의 동적점탄성 실험에서는 주파수$({\omega})$가 증가함에 따라 저장탄성률(G#)와 손실탄성률(G@)은 증가하였으며 양(+) 기울기로 G#수치가 G@수치보다 높게 나타났다. 이는 고추장이 약한 겔과 같은 구조적 특성을 갖고 있으며 또한 shear-thinning 거동을 가지고 있음을 나타낸다. 정적점탄성 실험에서 고추장의 총고형분 함량에 따라서 순간탄성 변형$(J_0)$과 지연탄성변형$(J_1)$은 총고형분 함량이 증가함에 따라서 감소하였으며 점도$({\eta}_N)$와 지연시간 $({\tau}_1)$은 증가하였다. 따라서 고추장은 농도가 증가함에 따라 보다 탄력적이며 안정된 구조를 형성하고 있음을 알 수 있었다.

• International Journal of Industrial Entomology and Biomaterials
• /
• v.45 no.2
• /
• pp.70-77
• /
• 2022

Wet-spun regenerated silk fibroin (RSF) fibers have been extensively studied owing to their 1) useful properties as biomaterials, including good blood compatibility and cyto-compatibility; 2) the various methods available to control the structural characteristics and morphology of the fiber, and 3) the possibility of fabricating blended fibers and new material-embedded fibers. In this study, silk nanofibrils prepared using a new method were embedded in RSF to fabricate wet-spun silk nanofibril/RSF composite fibers. Up to 2% addition of silk nanofibril, the silk nanofibril/RSF dope solution showed slight shear thinning, and the G' and G" of the dope solution were similar. However, above 3% silk nanofibril content, the viscosity of the dope solution significantly increased. In addition, shear thinning was remarkably evident, and the G' of the dope solution was much higher than the G", indicating a very elastic state. As the silk nanofibril content was increased, the wet-spun silk nanofibril/RSF composite fiber became uneven, with a rough surface, and more beaded fibers were produced. Scanning electron microscopy observations revealed that the beaded fibers were attributed to the inhomogeneous dispersion and presence of agglomerates of the silk nanofibrils. As the silk nanofibril content and RSF concentration increased, the maximum draw ratio decreased, indicating the deterioration of the wet spinnability and post-drawing performance of silk nanofibril/RSF.

• Korea-Australia Rheology Journal
• /
• v.14 no.4
• /
• pp.203-207
• /
• 2002

Particle-particle interaction is of great importance in the study of suspension rheology. In this research we have investigated the hydrodynamic interaction between two identical cylinders in viscoelastic fluids numerically as a model problem for the study of viscoelastic suspension. We confine two neutrally buoyant cylinders between two parallel plates and impose a shear flow. We determine the migration velocity of two cylinders. The result shows that cylinders move toward or away from each other depending upon the initial distance between them and that there is an equilibrium distance between two cylinders in viscoelastic fluids regardless of the initial distance. In the case of Newtonian fluid, there is no relative movement as expected. The results partly explain the chaining phenomena of spherical particles in shear flows of viscoelastic fluids.

• Korea-Australia Rheology Journal
• /
• v.12 no.3_4
• /
• pp.181-186
• /
• 2000

Rheological Properties of polypropylenes having different molecular structures (linear polypropylene (PPL) and branched one (PPB)) were studied. Both the extensional flow and oscillatory shear flow properties were checked. Especially, the melt strength of polypropylenes having various shear history were investigated by using in-house-made Rheometer (called SMER). Compared to linear polypropylene, the branched polypropylene shows enhanced melt strength during extensional flow due to the retarded relaxation of molecules. When the slope of melt tension was plotted against take up speed of melt strand, the characteristic peak was observed in case of branched polypropylene, while the linear polypropylene shows only monotonously decreasing pattern. This entanglement was partially disrupted by physical forces such as shear during melt extrusion. However, the melt strength of PPB after multiple extrusion is still higher than PPL, implying the loss of elasticity during multiple extrusion is not so comprehensive. On dynamic experiments, PPB shows typical shear thinning behavior and the tangent delta of PPB is lower than PPL, reflecting high elasticity of PPB.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.11a
• /
• pp.137-140
• /
• 2005

Exfoliated nanocomposites of polypropylene/layered silicate were prepared by a melt compounding process using maleic anhydride modified polypropylene (PP-g-MAH) and organoclay. It was found that polypropylene/layered silicate nanocomposites exhibited remarkable reinforcement compared with the pure polypropylene or conventional composite filled with agglomerated organoclay. The polypropylene /layered silicate nanocomposites showed stronger and earlier shear thinning behaviors and outstanding strain hardening behavior than pure polypropylene or other conventional composites in shear and uniaxial elongational flows, respectively. We simulated rheological modeling for the pure polymer matrix and polypropylene/layered silicate nanocomposite in shear and elongational flows using K-BKZ integral constitutive equation. The two types of K-BKZequations have been examined to describe experimental results of shear and uniaxial elongational viscosities of pure polypropylene and polypropylene/layered silicate nanocomposite.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1298-1302
• /
• 2000

Electrorheological(HER) and magnetorheologica(MR) fluids have a unique ability to increase the dynamic yield stress of the fluid substantially when electric or magnetic field is applied. ER and MR fluid-based dampers are typically analyzed using Bingham-plastic shear flow analysis under Quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post-yield shear thinning and shear thickening. To model these, the constant post-yield plastic viscosity in Bingham model can be replaced with a power-law model dependent on shear strain rate that is known as the Herschel-Bulkley fluid model. The objective of this paper is to predict the damping forces analytically in a typical ER bypass damper for variable electric field, or yield stress using Herschel-Bulkley analysis.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.29 no.5
• /
• pp.860-864
• /
• 2000

The steady and dynamic shear rheological properties of traditional kochujang fermented at three different temperatures (20${^circ}C$, 25${^circ}C$ and 30${^circ}C$) were studied. Flow of kochujang samples showed time dependence, which was quantitatively described by the Weltman model, Kochujang samples were highly shear thinning fluids (n=0.25~0.27) with large magnitudes of Casson yield stresses (1.09~1.21 kPa). Consistency index (K) and apparent viscosity (${\eta}_{a,20}$) increased with increase in fermentation temperature of kochujang. Storage (G') and loss (G") moduli increased with increase in frequency (ω), while complex viscosity (${\eta}^{\ast}$) decreased. Based on dynamic shear data, kochujang samples exhibit structural properties similar to weak gels. The complex and steady shear viscosities at different fermentation temperatures followed the Cox-Merz superposition rule with the application of the shift factor (a=0.011~0.016).