Steady Shear Experiments Research Articles

Preparation and rheological characterization of intercalated polystyrene/organophilic montmorillonite nanocomposite

AbstractPolystyrene (PS)/organophilic montmorillonite (OMMT) clay nanocomposites were prepared by a solvent casting method using chloroform as a cosolvent. Intercalation of the OMMT in the PS matrix was achieved as revealed by X‐ray diffraction. The IR spectra of the products indicated that the OMMT is homogeneously dispersed in the PS matrix. A thermogravimetric analysis (TGA) showed that the onset temperature increases linearly with the clay content. The glass‐transition temperature of the PS, examined using differential scanning calorimetry, had a trend similar to that from the TGA. The rheological properties of the PS/OMMT nanocomposites were also investigated via a rotational rheometer with a parallel plate geometry, and they exhibited sharper shear thinning and increased storage and loss modulus with clay content. Furthermore, the shear viscosity obtained from the steady shear experiment was well correlated with the complex viscosity obtained from the oscillatory experiment via the Cox and Merz relation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2106–2112, 2003

Rheological and morphological properties of high‐density polyethylene and poly(ethylene–octene) blends

AbstractThe rheological and morphological properties of blends based on high‐density polyethylene (HDPE) and a commercial ethylene–octene copolymer (EOC) produced by metallocene technology were investigated. The rheological properties were evaluated in steady and dynamic shear experiments at 190°C in shear rates ranging from 90 s−1 to 1500 s−1 and frequency range between 10−1 rad/s and 102 rad/s, respectively. These blends presented a high level of homogeneity in the molten state and rheological behavior was generally intermediate to those of the pure components. Scanning electron microscopy (SEM) showed that the blends exhibit dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2240–2246, 2002

Influence of Droplet Size on the Rheological Behavior of Emulsions

This study examined emulsions with two different mean droplet diameters under steady and oscillatory shear flow. The oscillatory experiments yielded results consistent with the steady shear experiments. A nearly constant increase in the complex shear modulus with frequency was observed over a wide range of concentration; as a result the difference in the moduli was nearly constant over the frequency range examined.

Effects of shear flow on a polymeric bicontinuous microemulsion: Equilibrium and steady state behavior

We have investigated the effects of shear flow on a polymeric bicontinuous microemulsion using neutron scattering, light scattering, optical microscopy, and rheology. The microemulsion consists of a ternary blend of poly(ethyl ethylene) (PEE), poly(dimethyl siloxane) (PDMS), and a PEE–PDMS diblock copolymer. At equilibrium, the microemulsion contains two percolating microphases, one PEE rich and the other PDMS rich, separated by a copolymer-laden interface; the characteristic length scale of this structure is 80 nm. Low strain amplitude oscillatory shear measurements reveal behavior similar to that of block copolymer lamellar phases just above the order–disorder transition. Steady shear experiments expose four distinct regimes of response as a function of the shear rate. At low shear rates (regime I) Newtonian behavior is observed, whereas at intermediate shear rates (regime II) development of anisotropy in the morphology leads to shear thinning. When the shear rate is further increased, there is an abrup...

Rheology of Concentrated Isotropic and Anisotropic Xanthan Solutions. 1. A Rodlike Low Molecular Weight Sample

The rheology of a rodlike xanthan sample (Fraction X13F3, Mw = 1.54 × 105 g/mol) has been studied in aqueous NaCl (0.01, 0.1, 1.0 M) in oscillatory and steady shear experiments. Polymer concentrations W (in weight percent) spanning the isotropic, biphasic, and fully anisotropic regimes of the lyotropic liquid crystalline phase diagram have been investigated. The rheological parameters increase as power law functions of W in the isotropic regime, decrease with higher power law exponents in the biphasic regime, and change very slowly in the fully anisotropic regime. The peak in plots of steady shear viscosity η against W shifts toward lower W with increasing shear rate γ, because of the shear-induced orientation. In contrast, peaks in the plots of the complex viscosity η*, storage modulus G‘, and loss modulus G‘ ‘ are independent of frequency ω, because shear-induced orientation is minimal under conditions of small strain. Power law curves fit to η*, G‘, and G‘ ‘ in the isotropic, biphasic, and anisotropic...

Effect of surfactant concentration on the formation and viscoelasticity of anionic wormlike micelle by the methods of rheology and freeze-fracture TEM

Wormlike micelles and network structures were obtained for the samples with the anionic surfactant, sodium dodecyl trioxyethylene sulfate (SDES), and multivalent counterion electrolyte AlCl3 fixed in a proper concentration according to rheological measurements and the technique of freeze-fracture transmission electron microscopy (FF-TEM). The characteristics of a non-Newtonian fluid and the phenomenon of shear-induced structures transition were acquired from the steady-shear experiments. The TEM micrographs show the coexistence of wormlike micelles, entangled network structures, rod- and sphere- like micelles in the solutions. The Cole-Cole plot shows the rheological behavior of the non-linear viscoelasticity, the departure from the Maxwell model, and a relaxation time that is not simple. The plateau modulus G0 and the relaxation time τ were also investigated to express the rheological properties of the wormlike micellar solutions.

Characterization of polymer dispersions by Fourier transform rheology

Fourier transform rheology is a very sensitive technique to characterize non-linear rheological fluid properties. It has been applied here for the first time to polymer dispersions in water and the results are compared to those from conventional rheology, namely steady and small amplitude oscillatory shear experiments. The investigated systems are mainly based on styrene and n-butylacrylate.

Dynamics of Kink Bands in Layered Liquids: Theory and in Situ SAXS Experiments on a Block Copolymer Melt

We consider the dynamics of an isolated kink band within an otherwise well-aligned lamellar block copolymer (or other smectic A liquid crystal) subjected to a macroscopic shear flow. We find on geometrical grounds that normal relative motion of the tilt boundaries that delineate such a band, relative to the normal velocity of the fluid, can occur only if there is jump in the tangential component of the fluid velocity across the boundary. We show that such tangential slippage should be negligible for well-developed bands with narrow boundaries. These observations lead to a simple description of the evolution of an idealized kink band, in which the kink bandwidth remains constant after the formation of narrow tilt boundaries, and the tilt boundaries rotate as material surfaces in a shear flow. The resulting prediction for the rate of rotation of the layers within such a band is confirmed by in situ small-angle X-ray scattering (SAXS)-steady shear experiments, which measure the evolution of the distribution ...

Viscoelasticity of biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(ethylene oxide)

The viscoelastic properties, measured via both steady shear and oscillatory experiments, for blends of biodegradable poly(3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) were examined. We observed that PHB/PEO blends are miscible. The first normal stress difference, the shear stress, and the shear viscosity (obtained from the steady shear experiment) were correlated with the storage modulus, the loss modulus, and the complex viscosity (obtained from the oscillatory experiment) via either the Cox and Merz rule or other empirical equations. For biodegradable PHB/PEO blend systems, we found that both the viscous and the elastic behavior from the steady shear experiment are qualitatively related to those from the oscillatory experiment.

SYNTHESIS AND VISCOELASTIC BEHAVIORS OF POLY(ANILINE-CO-O-ETHOXYANILINE) PARTICLES SUSPENDED ELECTRORHEOLOGICAL FLUID

Copolyanilines are synthesized by a chemical oxidation of aniline and o-ethoxyaniline with various molar ratios in an acidic media, and then characteristics of these polymers such as chemical structure, particle size and the particle size distribution were examined by using FT-IR, SEM and particle size analyzer, respectively. Suspensions of copolyaniline containing ethoxy group, namely poly(aniline-co-o-ethoxyaniline), in silicone oil have been investigated as one of many potential candidates for dry-base electrorheological (ER) fluid systems. Rotational rheometer (Physica) equipped with a high voltage generator was used to characterize the rheological properties of ER fluids from both steady shear and dynamic tests. From the steady shear experiment, we obtained flow properties and found that ER fluids exhibited the yield phenomenon. On the other hand, viscoelastic property was also obtained from the dynamic experiment. Since viscoelastic properties for ER fluids are mainly dominated by the particle chain structure, the state at different time scale was analyzed from the rheological parameters such as storage modulus (G'), loss modulus (G'') and tan δ. We conducted a strain amplitude sweep at 1 Hz under an applied electric field to determine a linear viscoelastic region first. The G' and G'' were then measured by a frequency sweep from 0.1 to 100 Hz in the linear viscoelastic region.

Rheology of compatibilized immiscible viscoelastic polymer blends

Rheological behavior of a PS/PE model viscoelastic immiscible blend compatibilized by two types of interfacial modifiers was investigated. Dynamic, steady shear, and transient experiments were performed to probe the effect of the interfacial modification on the rheological behavior of the blend. While the effect was relatively small in dynamic and steady shear experiments, significant signature of the presence of the copolymer was observed in transient experiments after start up of shear flow. The magnitude of the departure from Doi-Otha theory (worked out for non-compatibilized blends) was evaluated.

In-situ Measurements of Electrorheological Response and Electric Properties of Ferroelectric Barium Titanate/Silicone Oil Suspension.

Electrorheological response of ferroelectric BaTiO3 / silicone oil suspension was experimentally studied with in-situ measurements of electric conductivity and dielectric permittivity in ranges of electric field strength (0-2kV/mm) and field frequency (100-5000Hz) under steady shear and shear stress sweep. In steady shear experiments, conducted at shear rates of 100 and 200s-1, shear stress increased with time accompanied by increases in the conductivity and the permittivity. The evolution of these electric properties suggested the growth of particle aggregation in the suspension. The shear stress at each time increased with field frequency, reached maximum value around 103Hz, and then declined. The change in the shear stress well corresponded to the change in the permittivity. An empirical relation of Δτ ∝(Δε rΕ )2 , observed for silica particle / silicone oil (Saimoto et al.,1999), was applicable to the present suspension, where Δτ is generated shear stress, Δεr generated dielectric permittivity, and Ε electric field strength. In the shear stress sweep experiments, hysteresis behavior was observed. Longer sweep period induced larger yield stress due to the growth of the aligned particles during the application of electric field. A drastic decrease in the permittivity around a yield point indicated collapse of the aggregative structure. A correlative behavior was observed between changes in the yield stress and the value of ΔεrΕ.

Electrorheological characterization of zeolite suspensions

The rheological properties of the electrorheological (ER) fluids prepared from commercial zeolites 3A, 5A and 13X suspended in silicone oil were investigated through steady shear and oscillatory shear experiments. Dielectric spectra of the fluids were also measured to examine their possible correlation with the flow behavior of the ER fluids. Among the zeolite ER fluids investigated, the ER fluid using 13X showed the best performance and had the shortest relaxation time of an interfacial polarization. Viscoelastic behavior was observed in the dynamic test under the applied electric field. The elasticity increased with the strength of the electric fields under linear viscoelastic conditions.

Viscoelastic characterization of biodegradable poly(3-hydroxybutyrate- co-3-hydroxyvalerate)

The viscoelastic properties of microbial biodegradable copolymers containing 3-hydroxybutylate (3HB) and 3-hydroxyvalerate (3HV) were investigated as well as the reference homopolymer, poly(3-hydroxybutylate) (PHB), by plotting the first normal stress difference ( N 1) versus shear stress ( τ s) and the storage modulus ( G′) versus the loss modulus ( G″). At low shear rates, the N 1s of the copolymers were higher than that of PHB, and at high frequencies, the G′s of the copolymers were lower than that of PHB. To examine the rheological properties of biodegradable copolymers, we used a modified Cole–Cole plot ( N 1 versus τ s and G′ versus G″). From these plots, we found that the elastic behavior from steady shear experiment is closely related to that of the dynamic oscillatory experiments for the biodegradable copolymer.

Rheological behavior of flexible elongated micelles: temperature effect in an isotropic phase

We present experimental results on the linear and non-linear rheology of elongated flexible micelles with salt. Steady shear experiments were carried out on aqueous surfactant solutions made of cetylpyridinium chloride and sodium salicylate in 0.5M brine. The isotropic phase of entangled micelles was investigated for total surfactant mass fraction φ between 4 and 14% and for temperatures ranging from 25 to 39°C. The viscosity curves show clearly four distinct domains: a Newtonian region (I) followed by a shear thinning part which starts above a critical shear rate γ̇c then an unstable zone (III) and finally a second shear thinning behavior (IV) at very high shear rates. The viscosity decrease in domain II can be related to the disentanglement of the micelles and the apparition of large scale anisotropic structures which grow and become more pronounced when the shear rate is increased. This phenomenon is characterized by a constant shear stress value σc in flow curves. A temperature dynamic phase diagram has been derived from the σc values.Measurements of steady shear viscosity by temperature sweeps at different shear rates indicate that the viscosity remains constant until a critical temperature is reached then falls abruptly. This behavior is only noticed for high enough shear rates corresponding to region IV.Domains I and II have been fitted using both Carreau model and a power law. The Newtonian viscosity η0 is described by an Arrhenius relationship. The critical shear rate γ̇c required to orient the micelles in the flow direction is found to increase with temperature. However, the exponent of the power law is independent of temperature. For each mass fraction, viscosity curves at various temperatures are well superposed on a master curve when appropriate reduced variables are used. Interpretation of unstable and shear thinning behaviors observed in the third and fourth parts, respectively, is in progress.

Nonlinear shear and extensional rheology of long-chain randomly branched polybutadiene

We present nonlinear shear and uniaxial extensional measurements on a series of polybutadienes with varying amounts of long-chain, random branching. Startup of steady shear experiments is used to evaluate the damping function of the melts. The damping function is found to show a trend toward decreased dependency on strain with increasing branching content. Interior chains, which are believed to be responsible for changing the damping function, are calculated to comprise less than 3 wt % of the melt. Extensional measurements are used to investigate the role of branching in strain hardening. We show that samples with increased branch contents do show larger deviations of the transient Trouton ratio from the linear viscoelastic limit of three. However, we also show that the extensional data can be fit using parameters determined solely by the shear measurements. Furthermore, we show that the changes in the damping function seen in shear have little impact on extensional behavior. The extensional behavior of the melt is found to be most affected by changes in the relaxation spectra which can result from both branching and increases in the high end of the molecular weight distribution. This statement runs contrary to the often expressed view that strain hardening behavior in extension is exclusively produced by branching.

Rheological properties of guar galactomannan and rice starch mixtures II. Creep measurements

The effect of particulate inclusions, or ‘fillers’, on the rheological properties of a typical polysaccharide entanglement solution (guar galactomannan/water) have been studied. Earlier steady shear experiments have shown an apparent upswing of the viscosity-shear rate profiles at low shear rates, with higher filler concentrations (Rayment et al., 1995). In creep experiments, a low constant stress is applied to the sample. In the present paper, the creep experimental data have been compared to the steady shear flow behaviour fitted by the yield stress modified Cross equation (introduced in Part I of this series). The apparent zero-shear viscosity and yield stress parameters have been constrained in a number of ways in the model to establish the effect of these parameters on the modified Cross model. Although the creep data appears to alter the precision of the modified Cross equation, due to the low shear rates accessed, the apparent upswing of the steady shear data at low shear rates appear to be supported by the data described in this paper. This lends further credibility to the scaled filler models introduced previously.

Rheological Behavior of a Dispersion of Small Lipid Bilayer Vesicles

Rheological behavior of a dispersion of small nearly-unilamellar phospholipid bilayer vesicles has been investigated. We conducted steady-state shear experiments and linear viscoelastic experiments. In the dilute and semidilute regime the rheological behavior is similar to that of a hard-sphere dispersion as reported in the literature for viscoelastic measurements, but now also observed in steady shear experiments. The effect of the main acyl-chain phase transition, taking place at 23 °C, can be described with an increase of the effective volume fraction. As a result, with temperature variation one can obtain effective volume fractions larger than the maximum packing fraction for hard spheres. Near and above the maximum packing fraction a dynamic yield stress τy and a frequency independent storage modulus G‘ develop. In this concentration regime the rheological behavior is determined by the interplay between vesicle deformation and the intervesicle interaction, and so far, there is no indication which phenomenon is dominant. A comparison with recently reported measurements suggests that G‘ is proportional to a-3, where a is the vesicle radius. Furthermore, we show that τy ≈ γcG‘ which is in agreement with theory. Here τy is the dynamic yield stress and γc the critical strain which indicates the transition to nonlinear behavior in a viscoelastic experiment. There is a striking resemblance between our high concentration results and those reported in literature for vesicles in the so-called onion phase. To the best of our knowledge this is the first rheological study for concentrated nearly-unilamellar vesicle dispersions with volume fraction and temperature as variables.

Electrorheological characterization of polyaniline dispersions

Suspensions of polyaniline in silicone oil have been investigated as potential candidates for dry-base electrorheological (ER) fluid systems. Polyaniline was synthesized by a chemical oxidation of aniline in an acidic media. Its optimum conductivity (in the semiconductive range) for ER purposes was achieved by adjusting the pH of an aqueous solution containing polyaniline particles. ER experiments were conducted with a Haake rheometer for steady shear experiments to investigate the effects of imposed electric fields, the polymerization temperature (molecular weight), and the dispersing oil on ER performance. ER properties of polyaniline suspensions were found to be improved by increasing both the imposed electric field and the polymerization temperature of the used polymer. Suspensions using kerosene also show greater ER effect than that using silicone oil because of the smaller dielectric constant of kerosene than that of silicone oil. A scaling law is introduced to analyse the ER data.

The viscosity and sedimentation of aggregating colloidal dispersions in a Couette flow

In order to interpret the time dependence of the measured torque in a steady shear experiment on an aggregating dispersion, a microrheological model has been used in which two existing models are integrated. In this microrheological model, a theory for fractal aggregation in shear flow is combined with a theory for the sedimentation and resuspension of non‐colloidal hard spheres. The former theory describes the viscosity as a function of shear rate, while the latter predicts the stress increase in a Couette device due to sedimentation. The connection between the two theories is made by identifying the aggregate parameters with the hard sphere parameters (size and volume fraction). The parameters of the aggregates as a function of shear stress are obtained by measuring a flow curve before sedimentation effects become significant and fitting this curve with the fractal aggregation theory. During the sedimentation, the aggregate size and volume fraction become a function of both time and position in the rheometer. Taking this into account, the predicted stress increase as a function of time is found to describe the experiments rather well. This result corroborates both of the existing theories.