• Journal of Pharmaceutical Investigation
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• v.25 no.3
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• pp.213-221
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• 1995

The steady shear flow properties of six kinds of commercial toothpastes were measured using a concentric cylinder type rheometer. In this paper, the shear rate and temperature dependencies of their flow behavior were investigated and the validity of the Casson and Herschel-Bulkley models was examined. Further, the flow properties over a wide temperature range were quantitatively evaluated by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) Toothpastes are plastic fluids with a yield stress and their flow behavior shows shear-thinning characteristics. (2) With increasing temperature, the degree of shear-thinning becomes weaker and the Newtonian flow behavior occurs at a lower shear rate range. (3) The Herschel-Bulkley model is more effective than the Casson model in predicting their flow behavior. (4) As the temperature increases, the yield stress, plastic viscosity and consistency index become smaller, on the contrary, the flow behavior index becomes larger.

• Korea-Australia Rheology Journal
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• v.17 no.4
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• pp.191-198
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• 2005

The static and dynamic rheological behavior of concentrated sodium dodecylsulfate (SDS) stabilized, deformability controllable polydimethylsiloxane (PDMS) emulsions is reported and comparisons made with silica (hard sphere) suspensions. Steady-mode measurements indicate 'hard' (viscoelastic) droplets behave as hard spheres, while 'soft' (viscous) droplets induce structural flexibility of the emulsion against shear. Dynamic-mode measurements reveal that viscoelasticity of droplets provides the great magnitude of elasticity for the 'hard' emulsion, while formation of planar films between droplets is the origin of the elasticity of 'soft' emulsions. Combination of steady and dynamic rheological behavior has enabled depiction of droplet structure evolution in relation to the shear stress applied, especially by taking advantage of the normal force that reflects the transient deformation of droplets.

• Food Science and Biotechnology
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• v.17 no.4
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• pp.780-786
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• 2008

Effect of acetylated starches (acetylated rice starch and acetylated tapioca starch) on rheological properties of hot pepper-soybean paste (HPSP) at different mixing ratios of rice flour (RF) and acetylated starch (AS) (10/0, 9/1, 8/2, and 7/3) was evaluated in steady and dynamic shear. All HPSP samples at $25^{\circ}C$ exhibited shear-thinning (n=0.31-0.36) and thixotropic behavior with high yield stresses and their steady flow curves were well described by power law and Casson models. The presence of AS resulted in the decrease in consistency index (K), apparent viscosity (${\eta}_{a,100}$), and yield stress (${\sigma}_{oc}$), and their predominant decreases were noticed at higher ratio of RF to AS (7/3 ratio). Arrhenius temperature relationship represents variation with temperature in the range of $5-35^{\circ}C$ with the high determination coefficients ($R^2=0.97-0.99$). Dynamic moduli (G', G", and ${\eta}^*$) values of HPSP samples mixed with AS were lower than those of HPSP with no added AS within the experimental range of frequency (0.63-62.8 rad/sec). Steady and dynamic shear rheological properties of HPSP samples seem to be greatly influenced by the presence of acetylated starch.

• Food Science and Biotechnology
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• v.15 no.6
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• pp.871-876
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• 2006

Rheological behavior of commercial hot pepper-soybean paste (HPSP) was evaluated in small amplitude oscillatory and steady shear tests. Storage modulus (G'), loss modulus (G"), and complex viscosity (${\eta}^*$) as a function of angular frequency (${\omega}$), and shear stress (${\sigma}$) as a function of shear rate (${\gamma}$) data were obtained for 5 commercial HPSP samples. HPSP samples at $25^{\circ}C$ exhibited a non-Newtonian, shear-thinning flow behavior with high yield stresses and their flow behaviors were described by power law, Casson, and Herschel-Bulkley models. Time-dependent flow properties were also described by the Weltman, Hahn, and Figoni & Shoemaker models. Apparent viscosity over the temperature range of $5-35^{\circ}C$ obeyed the Arrhenius temperature relationship with activation energies (Ea) ranging 18.3-20.1 kJ/mol. Magnitudes of G' and G" increased with an increase in ${\omega}$, while ${\eta}^*$ decreased. G' values were higher than G" over the most of the frequency range (0.63-63 rad/sec), showing that they were frequency dependent. Steady shear viscosity and complex viscosity of the commercial HPSP did not fit the Cox-Merz rule.

• Korea-Australia Rheology Journal
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• v.17 no.1
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• pp.1-7
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• 2005

Acrylonitrile-Butadiene-Styrene (ABS), polycarbonate (PC) and their alloys are an important class of engineering thermoplastics that are widely used for automotive industry, computer and equipment housings. For the process of recycling mixtures of ABS and PC, it is desirable to know how sensitive the blend properties are to changes in compositions. It was for this reason that blends of virgin ABS and virgin PC at five different compositions, namely, $15\%,\;30\%,\;50\%,\;70%$ and $85\%$ by weight of ABS were prepared and characterised by rheological and mechanical measurements. Rheological properties of these blends in steady, oscillatory and transient step shear and mechanical properties, namely, tensile strength, elongation-at-break and Izod impact strength are reported. The results show that PC behaves in a relatively Newtonian manner, but ABS exhibits significant shear thinning. The ABS-rich blends show a trend that is similar to that of ABS, while PC-rich blends, namely $0\%$ and $15\%$, exhibit a nearly Newtonian behaviour. However, at a fixed shear rate or frequency, the steady shear or the dynamic viscosity varied respectively in a non-mono-tonic manner with composition. Except for $15\%$ blend, the viscosities of other blends fall into a narrow band indicating a wide-operation window of varying blend ratio. The blends exhibited a lower viscosity than either of the two pure components. The other noticeable feature was that the blends at $70\%$ and $85\%$ ABS content had a higher G' than pure ABS, indicating an enhancement of elastic effect. The tensile yield strength of the blends followed the 'rule of mixtures' showing a decreasing value with the increase of ABS content in PC. However, the elongation-at-break and the impact strength did not appear to obey this 'rule of mixtures,' which suggests that morphology of the blends also plays a significant role in determining the properties. Indeed, scanning electron micrographs of the fracture surfaces of the different blends validate this hypothesis, and the $15\%$ blend is seen to have the most distinct morphology and correspondingly different behaviour and properties.

• Culinary science and hospitality research
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• v.8 no.3
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• pp.295-308
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• 2002

The effect of vinegar concentration (＋30%, 0% and -30%) on the emulsion stability of mayonnaise dressing was studied by the measurement of theological test and sensory evaluation. The emulsion stability of mayonnaise dressing increased with increase in vinegar concentration. The results of steady shear theological test indicated that C sample of the highest vinegar concentration (＋30%) exhibited higher emulsion stability than other samples. The dynamic shear datas were similar to steady shear theological data. The mayonnaise dressing samples showed time dependence, which was quantitatively described by the Weltman model. Parameters A and B indicated that the structure of C sample exhibited more stable than that of A (-30%) and B (0%) samples. The amount of oil separation was less than that of A and B samples. The results of sensory evaluation were similar to those of theological and emulsion tests.

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.201-212
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• 2004

Properties of polymer based nanocomposites depend on dispersion state of embedded fillers. In order to examine the effect of dispersion state on rheological properties, a new bi-mode FENE dumbbell model was proposed. The FENE dumbbell model includes two separate ensemble sets of dumbbells with different fric­tion coefficients, which simulate behavior of well dispersed and aggregated carbon nanotubes (CNTs). A new parameter indicating dispersion state of the CNT was proposed to account for degree of dispersion quantitatively as well as qualitatively. Rheological material functions in elongational, steady shear, and oscillatory shear flows were obtained numerically. The CNT/epoxy nanocomposites with different dis­persion state were prepared depending on whether a solvent is used for the dispersion of CNTs or not. Dis­persion state of the CNT in the epoxy nanocomposites was morphologically characterized by the field emission scanning electronic microscope and the transmission electron microscope images. It was found that the numerical prediction was in a good agreement with experimental results especially for steady state shear flow.

• Bulletin of the Korean Chemical Society
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• v.21 no.9
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• pp.875-881
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• 2000

We study the rheological properties of concentrated polymer solution and the melt under simple shear and elon-gational flow using Brownian dynamicssimulation. In order to describe the anisotropic molecular motion, we modifiedthe Giesekus' mobility tensor by incorporating the finitely extensible non-linear elastic (FENE) spring force into dumbbell model. To elucidate the nature of this model, our simulation results are compared with the data of FENE-P ("P"standsfor the Perterin) dumbbell model and experiments. While in steady state both original FENE and FENE-P models exhibit a similar viscosity response,the growthof viscosity becomes dissimilar as the anisotropy decreases and the flowrate increases. The steady state viscosity obtained from the simulation well describes the experiments including the shear-thinning behavior in shear flow and viscosity-thinning behavior in elongational flow. But the growth of viscosity oforiginal FENE dumbbell model cannot describe the experimental results in both flow fields.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.117-123
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• 2007

There has been considerable interest in recent years in field-responsive suspensions, which are of some importance in industry in many different applications. The microstructure of these materials is a significant issue which can be probed by rheological measurements. In this study, measurements were made of a magnetorheological fluid (MRF) under steady and oscillatory shear flow, with and without a magnetic field. Mathematical inversion was used to derive the relaxation time spectrum of the MRF from oscillatory shear data. Experimental evidence is presented of the gel-like properties of this MRF.

• Korea-Australia Rheology Journal
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• v.14 no.4
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• pp.189-201
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• 2002

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.