A numerical work is conducted in order to verify the phenomena which are observed in experiments for a Y-type junction of two laminar flow layers of a viscoelastic and Newtonian fluid with a relatively high-speed stratification, where the inertia of flows can not be neglected. A numerical technique based on Simplified Arbitrary Lagrangian-Eulerian (SALE) method is used for simulating a behavior of time-dependent interfacial stratified fluids. In comparison with experimental results, it is revealed that the present scheme predicts the wavy interfacial surface phenomena that can occur in the stratified flow geometry with a viscoelastic fluid at a specific combination of the Reynolds number and the Deborah number.
Experimental results on rheological behaviors of concentrated suspensions are presented. Suspensions of acryl-styrene copolymer particles with a radius of 45 nm dispersed in water was used as samples. Rheological properties were measured at particle volume fractions φ ranging from 0.177 to 0.462. The time-volume fraction superposition principle was found to be applicable for the suspensions, namely frequency dependence curves with different φ could be reduced to one master curve by shifting horizontally and vertically with shift factors, aφ and bφ. The reological data were rescaled using the effective volume fraction φeff calculated from the effective radius estimated as a sum of the Debye length and the particle radius. With the rescaling, the φ dependency of η0/ηm and η∞/ηm became in good agreement with those of ideal suspensions of rigid spheres, which shows that the Brownian contribution is the origin of the linear viscoelastic behavior. It is likely that the Brownian motion is affected by restraint of neighboring particles in the high φ region so that relaxation time may increase rapidly in the high φ region.
Structural development of the ternary self-assembly, comprising cetyltrimethylammonium chloride (C16CA), cetyl alcohol (C16OH) and water, proceeds gradually up to one month. This is monitored by the strain (γ) dependence of the dynamic modulus (G') and the loss modulus (G"). Cohesive energy, EC, of the formed structure increases over weeks. While G' increases monotonously with ω, G" exhibits two maxima when plotted against frequency. This is compatible with two arcs in the Cole-Cole plots, corresponding to two respectiv relaxation mechanisms. The relaxation strengths, IH and IL are attributed to relaxation of lamellae and the network of coagulated multilamellar vesicles, respectively. We therefore conclude that viscoelastic behaviors at the higher and lower frequency sides are associated with lamellae and the network of coagulated vesicles. Two DSC endothermic peaks at 61 and 64°C represent the melting point of lamellae and vesicles. When the aging time is less than one day, the melting enthalpy ratio (ΔHL/ΔHH) is less than unity, hence the coagulated structure of vesicles outweighs lamellae. Further increase in the lamellae is consistent with the increase in the relaxation strength ratio (IH/IL) obtained from the Cole-Cole plots.
Effects of base hydrophobicity on a flow behavior and a microstructure of aqueous suspension of core-shell type carboxylated polymer particle have been studis. The suspension was neutralized by NaOH, dimetylaminoethanol(DMAE), dimetylaminopropanol(DMAP) and dimetylaminobutanol(DMAB). Steady shear flow was measured with a coni-clinder rotational rheometer, and microstructure was examined with a dynamic oscillating shear method and the small angle X-ray scattering(SAXS) method. The hydrophobicity is DMAB>DMAP>DMAE>NaOH. The distance ξ between center to center of neighboring particles in ordered structure made of the particles was measured by SAXS method. In case of NaOH, the suspension indicated shear-thinning flow. Loss tangent tan δ was below 1(G'>G") in all frequency region and a diffraction peak in SAXS profile was detected. These results show the three dimensional network structure of ordered structure is formed in the suspension. As the hydrophobicity increased, viscosity and degree of shear-thinning decreased, tan δ became above 1 in almost frequency region and the height of diffraction peak decreased without changing ξ. These results suggest that, as the base hydrophobicity increased, the three dimensional network structure reduces to the isolated domain structure, though the distance between neighboring particles in ordered structure does not change.
Rheological behaviors and microstructures of aqueous suspensions of a bimodal core-shell type of carboxylated particles have been studied by varing a weight ratio of two particles. Diameters of these particles in the fully neutralized state were 176nm and 291nm, respectively. Steady shear flow was measured with a coni-cylinder rheometer, and the critical shear stress σc, defined as the stress at the transition point from Newtonian flow to shear thinning flow, was estimated. The distance ξ which is the center to center distance between neighboring particles in an ordered structure of the suspensions was estimated with the small angle X-ray scattering (SAXS) method. All suspensions tested exhibited psudoplatic flow and gave single diffraction peak in their SAXS profiles. This result suggests that an alloy structure made of the bimodal particles is formed in these suspensions. As a weight fraction of large particle increased, viscosity and a degree of shear-thinning of the suspension decreased, and also ξ decreased. The relationship between σc and ξis represented as σc=4kT/3πξ3. This indicates that σc is dominated by thermal motion of lattice of the ordered structure. These findings indicate that the shear-rate dependence of the viscosity of the suspension is attributed to dynamical competition between the thermal motion and the hydrodynamic motion under shear flow, and the mechanism is applied to not only uni-modal suspensions but also bimodal suspensions.
This paper repotrs strain and frequency dependencies of dynamic viscoelasticity of commercial plain yoghurts and trial foods for swallowing disorders. We prepared four test samples adjusting hardness to a level similar to that of commercial plain yoghurts. Guar gum and modified starch were used as ingredients for preparation of two samples, respectively. Commercial plain yoghurts and modified starch samples exhibited viscoelastic behaviors strongly dependent on shear, while they behaved as nearly elastic material in the linear viscoelastic region. These properties are shown to be consistent to the swallowing mechanism to which well organized cooperative motions of several organs are related. Viscoelastic properties of guar gum samples were found to be quite different from those of commercial plain yoghurts, which suggests that modified starch is a better ingredient than guar gum for preparation of test samples and for detailed research on swallowing disorders.
From a simple calculation considering no thermodynamic requirement of maintaining uniform density, we estimated the effects of spatial confinement on the dielectric relaxation of model block copolymer chains having type-A dipoles. The results were utilized to discuss the relative importancc of these requirement and confinement in the block chain dynamics. For a tail (tethered) chain composed of N segments as well as for loop/bridge chains composed of 2N segments, all confined in a lamella of thickness L=N1/2b (b=segmental step length), the terminal relaxation was moderately faster, its mode distribution was slightly broader, and the dielectric intensity was considerably smaller than those of the same chains in free space. These effects of the spatial confinement were identical for the bridge and loop (either in the knotted or unknotted configuration) and nearly the same also for the tail. The dielectric behavior expected from this calculation was quite different from the behavior of actual type-A blocks. This result strongly suggests that the block chain dynamics is affected much moer significantly by the requirement of maintaining uniform density than by the spatial confinement.
Rheological properties and structure of the gel phase formed in potassium palmitate ( potassium n-hexadecanoate )/water colloidal systems have been investigated using dynamic viscoelastic measurements and small angle X-ray scattering(SAXS). This colloidal systems formed lamellar structure in the gel phase which are stable at 25°C. Lamellar repeat distance, which is the thickness of the surfactant layer puls water layer, is linearly related to φW/φS, where φW and φS are the weight fraction of water and surfactant, respectively. From this analysis, the thickness and the density of the surfactant layer and the surface area per surfactant molecule are estimated as 2.21nm, 1.11g/cm3, and 0.399nm2, respectively. The values of storage modulus G' and loss modulus G” of the colloidal systems are almost equal over a wide range of frequency and they increase with increasing angular frequency ω in proportion to ω0.4. These viscoelastic properties of the gel phase differ from that of the lamellar liquid crystalline phase formed in the surfactant/water colloidal systems, although both phases have lamellar structure.