High Shear Rate Region Research Articles

Effect of maleic anhydride-grafted ethylene–propylene rubber on the mechanical, rheological and morphological properties of organoclay reinforced polyamide 6/polypropylene nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were compatibilized with maleic anhydride-grafted ethylene–propylene rubber (EPRgMA). The blends were melt compounded in twin screw extruder followed by injection molding. The mechanical properties of PA6/PP nanocomposites were studied by tensile and flexural tests. The microstructure of the nanocomposite were assessed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The dynamic mechanical properties of the PA6/PP blend-based nanocomposites were analyzed by using a dynamic mechanical thermal analyzer (DMTA). The rheological properties were conducted from plate/plate rheometry via dynamic frequency sweep scans. The melt viscosity in a high shear rate region was performed by using a capillary rheometer. The strength and stiffness of the PA6/PP-based nanocomposites were improved significantly with the incorporation of EPRgMA. Adding EPRgMA to the PA6/PP blends resulted in a finer dispersion of the PP phase. TEM and XRD results revealed that the organoclay was dispersed more homogeneously in the presence of EPRgMA, however, mostly in the PA6 phase of the blends. DMTA results showed that EPRgMA worked as an effective compatibilizer. The storage ( G′) and loss moduli ( G″) assessed by plate/plate rheometry of PA6/PP blends increased with the incorporation of EPRgMA and organoclay. Furthermore, the apparent shear viscosity of the PA6/PP blend increased significantly for the EPRgMA compatibilized PA6/PP/organoclay nanocomposite. This was traced to the formation of an interphase between PA6 and PP (via PA6-g-EPR) and effective intercalation/exfoliation of the organoclay.

Rheological Characteristics of Ethylene Vinyl Acetate (EVA)/Silane Nanocomposites

EVA/tetraethylorthosilane(silane) nanocomposites were prepared. Rheological properties were studied in both dynamic and steady modes at 150oC. The rheological properties of the nanocomposites are strongly affected by silane dispersed in EVA matrix. As silane content incresed, the polymer strength increased due to interconnections between filler clusters which can be disrupted by high shear rate (in steady mode). The degree of silane dispersion in the EVA matrix decreased with increasing silane content, leading to a “pseudo-solid-like” behaviour. The samples showed viscous and elastic behaviour at low- and high-shear rate regions, respectively. The nanocomposite films were almost as clear as EVA film.

New Method for the Detection of Thrombus Formation in Cardiovascular Devices: Optical Sensor Evaluation in a Flow Chamber Model

We proposed a new method of detecting the onset of thrombus formation based upon the backscattered light intensity changes caused by the alteration of blood flow behavior in the cardiopulmonary devices. In an optical senor based upon the First Order Scattering theory, the relationship between the backscattered light intensity and hematocrit exhibited a monotonically decaying curve for the hematocrit level greater than 45%. To distinguish the effect either by thrombus formation or erythrocyte aggregation on the back-scattered light intensity with a flow chamber connected to a rabbit arterial-venous bypass model, we generated an oscillatory flow using a roller pump and analyzed the results using a Fast Fourier Transform (FFT) method. Our hypothesis was that the nonclotting blood flow would yield an unchanged fundamental spectral power density of the oscillation frequency generated by a roller pump, whereas the thrombus formation would attenuate its power. We measured the back-scattered light intensity in the flow chamber of high shear region and low shear region (n = 5). The blood flow rate was 40 ml/min with the roller pump. The activated clotting time and the hematocrit level were adjusted to 170 +/- 10 s with heparin and 35 +/- 5% with a phosphate buffered sulfate solution, respectively. As a result, the backscattered light intensity from the low shear rate region gradually diminished with time (p < 0.05; 0-5 minutes vs. more than 10-15 minutes), whereas that from the high shear rate region remained fairly constant. The experimental finding supported the hypothesis that the decrease of the backscattered light intensity and diminished spectral power density were caused by the aggregation or clotting erythrocytes. In conclusion, we found that the measurement of the average backscattered light intensity level together with FFT analysis of the backscattered light from the flowing blood is a valuable approach in detecting the onset of thrombus formation.

A modified model for non-newtonian viscosity behavior of Aureobasidium pullulans culture fluid

The culture fluid of the fungus Aureobasidium pullulans and the exopolysaccharide solution obtained by removal of the microbial cells exhibit a marked shear dependence of viscosity. The viscosity in a high shear rate region was a little higher than that predicted by a non-Newtonian viscosity equation derived previously on the basis of the concept of traveling force. In a sample exhibiting such high shear rate dependence, a hydrodynamic effect based on the fluid structure of the binding of contacting polymers and suspended microbial cells on viscosity becomes comparatively significant. A model for the shear rate dependence of the viscosity is needed to elucidate the mechanism of the viscosity behavior. A term concerning the increase in viscosity caused by the binding of polymers and the microbial cells suspended in a medium was added to the previous viscosity equation. The experimental shear dependence of the viscosity was well simulated by the modified viscosity equation.

The Kinetics of Shear-Induced Crystallization in Poly(Ethylene Terephthalate)

The kinetics of shear-induced crystallization in PET was studied. The shear-treated samples were obtained from Controlled Shear Rate apparatus (CSR, Figure 1) and the capillary viscometer. In the samples were observed the differences of crystallization behavior by DSC. The kinetic model suggested by Hoffman-Lauritzen, Nakamura was used to analyze experimental results. The crystallization behavior of shear-treated samples depended on temperature and shear stress. On the lower shear rate region, the rate of crystallization depended on shear stress and the growth rate induced by fluid flow reached the critical point in the region of a certain high shear rate. The empirical data were simulated by the suggested model.

NMR measurements and simulations of particle migration in non-newtonian fluids

Shear-induced migration of particles is studied during the slow flow of suspensions of neutrally buoyant spheres, at 50% particle volume fraction, in an inelastic but shear-thinning, suspending fluid. The suspension is flowing in between a rotating inner cylinder and a stationary outer cylinder. The conditions are such that nonhydrodynamic effects are negligible. Nuclear magnetic resonance (NMR) imaging demonstrates that the movement of particles away from the high shear rate region is more pronounced than for a Newtonian suspending liquid. We test a continuum constitutive model for the evolution of particle concentration in a flowing suspension proposed by Phillips et al., but extended to shear-thinning, suspending fluids. The fluid constitutive equation is Carreau-like in its shear-thinning behavior but also varies with the local particle concentration. The model captures many of the trends found in the experimental data, but does not yet agree quantitatively. In fact, quantitative agreement with a diffusive flux constitutive equation would be impossible without the addition of another fitting parameter that may depend on the shear-thinning nature of the suspending fluid. Because of this, we feel that the Phillips model may be fundamentally inadequate for simulating flows of particles in non-Newtonian suspending fluids without the introduction of a normal stress correction or other augmenting terms.

BROWNIAN DYNAMICS ANALYSIS OF CLUSTER STRUCTURES AND MAGNETIC CHARACTERISTICS OF FERROMAGNETIC PARTICLES SUBJECTED TO A SHEAR FLOW FIELD

We carried out Brownian dynamics analysis of a ferromagnetic colloidal system which is subjected to both shear flow and external magnetic fields and investigated the magnetic and rheological characteristics. The effects of the strength of magnetic field, particle interactions and shear rate on the magnetisation, the viscosity and the cluster formations are examined and discussed. The cluster structures in the ferromagnetic colloidal system and rheological characteristics of the system in both low and high shear rate regions are made clear.

Inhomogeneous viscosity fluid flow in a wide-gap Couette apparatus: Shear-induced migration in suspensions

The first portion of this two-part paper investigates the short time evolution of a low Reynolds number flow characterized by a spatially inhomogeneous viscosity within the annular domain between two widely separated concentric circular cylinders undergoing relative rotation. The viscosity is regarded as a material property and as such is convected with the fluid. Any possible “diffusion” of this viscosity is supposed negligible, at least in the short times of interest in our calculation. The initial viscosity field, assumed to be only slightly inhomogeneous, is expanded into a Fourier series with respect to the polar angle, and the contributions of the zeroth and first harmonics are subsequently addressed. Approximate short-time analytic solutions for the velocity and viscosity fields are obtained. In the second part of this paper the results of the preceding analysis are employed in an attempt to gain insight into the experimentally observed shear-induced migration of particles in suspensions being sheared in a wide-gap Couette apparatus. The connection of the inhomogeneous viscosity problem studied in the first part to such shear-induced migration phenomena lies in the assumption that the local viscosity of a suspension of (non-Brownian) particles is functionally dependent only upon the local suspended particle volumetric fraction. In such circumstances, the local transport of suspended particles corresponds to a concomitant transport of the local suspension viscosity and vice-versa. Subject to the foregoing interpretation and limited by algebraic tractability to short times, a global radial migration is predicted. It increases with an increase in the annular gap size between the cylinders and depends upon the phase angle between the rotating outer and inner cylinders, but not upon their relative circumferential velocity—a conclusion consistent with experimental observations. Further, to leading order, particle migration is found to be independent of purely radial viscosity disturbances (the zeroth harmonic) and to arise entirely from coupling between circumferential disturbances in the velocity and viscosity (i.e., particle concentration) fields. The solution also indicates that the high shear-rate region, proximate to the inner wall, may either become less viscous on average (thereby predicting net radial migration away from the high shear rate region) or, conversely, more viscous (corresponding to migration toward the high shear rate region migration). The latter case arises in circumstances that involve a large positive radial gradient in the viscosity’s first harmonic.

The effect of shear rates on gas separation performance of 6FDA-durene polyimide hollow fibers

We have determined the effect of shear rates within a spinneret on gas separation performance of asymmetric 6FDA-durene polyimide hollow fiber membranes. We purposely wet-spun the hollow fibers at different dope flow rates without drawing and with a constant ratio of bore fluid flow rate to dope flow rate in order to study the effect of shear within a spinneret during hollow fiber spinning on fiber morphology and gas separation performance. For the first time, we found there is a V (down and up) pattern for permeance versus shear rate relationship, while a Λ (up and down) pattern for selectivity versus shear rate relationship. At low shear rates, the permeances of non-polar molecules such as H 2, O 2, N 2, and CH 4 decrease, while their relative selectivities increase with an increase in shear rates. Once a certain shear rate is reached, all permeances increase, while their selectivities decrease with an increase in shear rates. In low shear rate regions, the decrease in permeance or increase in selectivity with increasing shear rates arises from the better molecular orientation and chain packing induced by shear. With increasing shear in high shear rate regions, the increase in permeance or decrease in selectivity is mainly attributed to relatively porous skin structures induced by the low viscosity nature of a power-law spinning fluid at high shear rates, fracture, and modified thermodynamics and kinetics of phase inversion process. This work suggests there may exist an optimum shear rate to yield optimal membrane morphology for gas separation. To our surprise, an increase in CO 2 permeance with increasing shear rates are possibly due to enhanced coupling effect between CO 2 and the highly oriented and closely packed fluoropolyimide molecular chains induced by shear.

Effects of acrylonitrile content on PC/ABS alloy systems with a flame retardant

To investigate the effect of a flame retardant on PC/ABS alloy systems, a reactive-type brominated epoxy resin was used as a flame retardant, and mixed with PC/ABS at various amount using a twin-screw extruder. The rheological, morphologi- cal, mechanical, and thermal properties were investigated as a function of acrylonitrile (AN) content in ABS. The shear viscosity of the PC/ABS blend increased as the AN content in ABS increased. Temperature drastically affected the shear viscosity in the ABS matrix, but not as much in the PC matrix. A blend of PC 50% containing AN 22% is suitable to process because its shear viscosity is low in the high shear rate region and its mechanical properties drastically increase in the beginning of the PC matrix. In addition, gradual increases of heat distortion temperature were observed in the entire range of the PC content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 417- 423, 2000

Hysteresis Behaviors of Poly (Naphthalene Quinone) Radical Electrorheological Fluid

As a potential electrorheological(ER) material, poly(naphthalene quinone) radical (PNQR) ER fluid was prepared, and its rheological behavior and hysteresis phenomenon were investigated. PNQR was synthesized by Friedel-Crafts acylation between naphthalene and phthalic anhydride, using zinc chloride as a catalyst at 256°C. A Physica rheometer equipped with a high voltage generator was used to measure the rheological properties of the ER fluids, which were prepared by dispersing PNQR in silicone oil at several particle concentrations. Shear stresses were observed to decrease as shear rate increased in the region of slow deformation rate. It was further found that ER fluid showed different hysteresis behaviors according to the shear rate ranges; thixotropy was observed in the low shear rate region (0.007-0.51/s) and anti-thixotropy in the high shear rate region (0.5-10001/s). Controlled shear stress mode was also applied to observe similar behaviors.

Velocity measurements of sheared granular flows

The flow behaviors of granular materials in a shear cell were experimentally studied. Different masses of granular materials were put in an annular shear device with a stationary upper wall and a constantly rotated lower wall. The image processing technique and the particle tracking method were employed to measure average particle velocities and fluctuating velocities in the streamwise and transverse directions. The granular flows consisted of a low shear rate region with higher and more uniform velocities in the lower test section, and a high shear rate region in the upper part. The velocities decreased with the height, while the fluctuations, granular temperature and shear rate increased with the height. The velocity fluctuations were anisotropic and were greater in the streamwise direction. The slip velocity and the low shear layer thickness were greater for the case with greater total granular mass.

Development of A Novel Instrument for Rheological Measurement of Printing Inks.

Rheological properties of emulsified inks are important for controlling printability because printing inks are emulsified by dampener water on press. This newly developed instrument can evaluate rheological properties of emulsified inks in the high shear rate region. Consequently, this instrument has greatly contributed for the designing of new products.

Melt rheology and morphology of physically compatibilized natural rubber-polystyrene blends by the addition of natural rubber-g-polystyrene

Blends of natural rubber (NR) and polystyrene (PS) were prepared by melt mixing in a Brabender plasticorder and by solution casting using chloroform as the casting solvent. Earlier studies have indicated that these blends are incompatible and immiscible, and their compatibility can be improved by the addition of a graft copolymer of NR and PS (NR-g-PS). The rheological behavior of these blends has been carried out in the presence and absence of the compatibilizer using a capillary rheometer and a melt flow indexer. The effects of blend ratio, processing techniques (melt mixing versus solution casting), shear stress, and temperature on the rheological behavior have been studied in detail. Both in the presence and absence of the copolymer, the blends showed a decrease in viscosity with an increase of shear stress, indicating pseudoplastic nature. Solution-cast blends showed a higher viscosity as compared to melt-mixed blends. The viscosity versus composition curve of both melt-mixed and solution-cast blends showed negative deviation from the additivity at a higher shear rate region. This is associated with the interlayer slip between the highly incompatible NR and PS phases. The effects of graft copolymer loading and temperature on solution-cast blends were studied, and it was found that as the copolymer loading increases, the shear viscosity increases. This is due to the high interfacial interaction between the two components in the presence of the copolymer. The copolymer, in fact, locates at the interface and makes the interface more broad. However, at higher loading of the copolymer, the viscosity of the blends decreases. This may be associated with the formation of micelles, which have a plasticizing action on the viscosity of the blends. Melt elasticity parameters like principal normal stress difference, recoverable elastic shear strain, and die swell were evaluated. Master curves have been generated using modified viscosity and shear rate functions that contain the melt flow index as a parameter. The extrudate morphology of the blends was studied using a scanning electron microscope. Addition of the copolymer reduces the domain size of the dispersed phase, followed by a leveling off at a higher concentration. The leveling off is an indication of interfacial saturation. The interparticle distance also decreased followed by a leveling off at a higher loading of the copolymer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2673–2690, 1998

Effect of ionic pendent groups on a polyaniline-based electrorheological fluid

Particles of semiconducting polyaniline and a copolyaniline bearing ionic substituents were synthesized. Electrorheological (ER) fluids using these particles were compared with each other with respect to their rheological properties and dielectric spectra. In the steady shear rheological experiment conducted at 3 kV/mm (DC) at 25°C, the copolymer system showed higher stress than the polyaniline system in the whole shear rate region. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra. Especially, the different behavior in the high shear rate region can be related to the electrical relaxation phenomena observed in the dielectric spectra.

Effect of ionic pendent groups on a polyaniline-based electrorheological fluid

Particles of semiconducting polyaniline and a copolyaniline bearing ionic substituents were synthesized. Electrorheological (ER) fluids using these particles were compared with each other with respect to their rheological properties and dielectric spectra. In the steady shear rheological experiment conducted at 3 kV/mm (DC) at 25°C, the copolymer system showed higher stress than the polyaniline system in the whole shear rate region. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra. Especially, the different behavior in the high shear rate region can be related to the electrical relaxation phenomena observed in the dielectric spectra.

Fiber Orientation Morphological Layers in Injection Molded Long Fiber Reinforced Thermoplastics

Flow-induced fiber orientation can vary significantly across the thickness of injection molded parts and is usually present in the form of through-thickness layers. In this work, fiber orientation was examined both on the flow plane and through the thickness. The thickness of a shell layer with fiber orientation in the flow direction and a core layer with a fiber orientation mainly transverse to the flow were measured via microscopy. The effect of filling speed and mold thickness on the molded plaque morphology was identified. Mold-filling simulations were undertaken in order to provide the characteristic shell and core layer fiber orientations as well as the frozen layer thickness at the end of filling and the gap-wise shear rate gradients. The combined frozen and high shear rate regions were correlated with the experimental shell layer thicknesses.

Numerical study of three-dimensional Kolmogorov flow at high Reynolds numbers

High-resolution numerical simulations (with up to 2563 modes) are performed for three-dimensional flow driven by the large-scale constant force fy = F cos(x) in a periodic box of size L = 2π (Kolmogorov flow). High Reynolds number is attained by solving the Navier-Stokes equations with hyperviscosity (-1)h+1Δh (h = 8). It is shown that the mean velocity profile of Kolmogorov flow is nearly independent of Reynolds number and has the ‘laminar’ form vy = V cos(x) with a nearly constant eddy viscosity. Nevertheless, the flow is highly turbulent and intermittent even at large scales. The turbulent intensities, energy dissipation rate and various terms in the energy balance equation have the simple coordinate dependence a + b cos(2x) (with a, b constants). This makes Kolmogorov flow a good model to explore the applicability of turbulence transport approximations in open time-dependent flows. It turns out that the standard expression for effective (eddy) viscosity used in K-[Escr ] transport models overpredicts the effective viscosity in regions of high shear rate and should be modified to account for the non-equilibrium character of the flow. Also at large scales the flow is anisotropic but for large Reynolds number the flow is isotropic at small scales. The important problem of local isotropy is systematically studied by measuring longitudinal and transverse components of the energy spectra and crosscorrelation spectra of velocities and velocity-pressure-gradient spectra. Cross-spectra which should vanish in the case of isotropic turbulence decay only algebraically but somewhat faster than corresponding isotropic correlations. It is verified that the pressure plays a crucial role in making the flow locally isotropic. It is demonstrated that anisotropic large-scale flow may be considered locally isotropic at scales which are approximately ten times smaller than the scale of the flow.

Microscopic Structure and Flow Behavior of Aqueous Suspension of Core-Shell Type Carboxylated Acrylic Particles

Microscopic structure of core-shell type carboxylated acrylic particles in aqueous suspension was studied by dynamic measurements and small-angle X-ray scattering, experiments, and relationship between the structure and flow behavior of the suspension was discussed. As the particle swells by addition of amine, the suspensions of various apparent volume fraction were prepared by changing amounts of 2-dimethylaminoethanol. Flow behavior was estimated by steady shear measurements.Flow behavior of the suspensions changes from Newtonian to pseudoplastic as apparent volume fraction increases. The suspensions of Newtonian flow in the all shear rate region (10-1s-1≤γ≤103s-1) have no flocculated structures. The suspensions of Newtonian flow in a lower shear rate region and pseudoplastic flow in a higher shear rate region have flocculated domain structures. The suspensions of pseudoplastic flow in all the shear rate region have three dimensional network structure. Both domain structure and three dimensional network structure are lattice-like ordered structures of the particles, and distance between two center of the particles in the ordered structures is 126nm. Creation of the ordered structure changes the suspension flow from Newtonian to pseudoplastic.

Shear-induced phase separation of complex fluids: The role of flow-concentration coupling.

We propose a classification scheme for the instabilities that might arise in sheared complex fluids. A central role is played by the coupling between the flow and the solute concentration, which is a combination of the parameters describing (a) the tendency of solute molecules to migrate to regions of small or high shear rates and (b) the variation of the viscosity with concentration. Using a mean field approach, we show that the nature and the geometry of the instability can be predicted from the knowledge of the coupling parameter, the diffuson coefficient, and the derivative of the stress with respect to the shear rate. We also successfully compare a description of the variation of the stress at and just beyond the instability threshold, with experimental results from a wormlike surfactant solution of ${\mathrm{CPClO}}_{3}$.