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Showing papers in "Rheologica Acta in 2002"


Journal ArticleDOI
TL;DR: In this paper, the reduced van-Gurp-Palmen plot (rvGP) is applied to model-type polymers to check whether these polymers exhibit features allowing one to classify them on basis of the corresponding linear viscoelastic data.
Abstract: Rheological data on monodisperse model-type polymers with a certain topology are available in the literature. A comparison between these series has not been made yet, mainly because the different chemical nature of these polymers inhibited a direct comparison. With the so-called reduced van-Gurp-Palmen plot (rvGP) this task has become possible and this article applies this plot to these model-type polymers. We check whether these polymers exhibit features allowing one to classify them on basis of the corresponding linear viscoelastic data. We define a characteristic point PC(Gred,c, δc) that represents the sample. By drawing all available points in rvGP-coordinates we obtain a topology map on which certain topologies cover distinct areas on this map. Unfortunately these areas overlap to some extent. For the unambiguous characterization of an unknown sample additional information is needed. We apply the topology map to metallocene poly(olefin)s.

300 citations


Journal ArticleDOI
TL;DR: In this paper, a survey on the influence of long-chain branching on the linear viscoelastic properties zero shear-rate viscosity and steady-state recoverable compliance of polyethylene melts is presented.
Abstract: This contribution presents a survey on the influence of long-chain branching on the linear viscoelastic properties zero shear-rate viscosity and steady-state recoverable compliance of polyethylene melts. The materials chosen are linear and slightly long-chain branched metallocene-catalyzed polyethylenes of narrow molecular mass distribution as well as linear and highly long-chain branched polyethylenes of broad molecular mass distribution. The linear viscoelastic flow properties are determined in shear creep and recovery experiments by means of a magnetic bearing torsional creep apparatus. The analysis of the molecular structure of the polyethylenes is performed by a coupled size exclusion chromatography and multi-angle laser light scattering device. Polyethylenes with a slight degree of long-chain branching exhibit a surprisingly high zero shear-rate viscosity in comparison to linear polyethylenes whereas the highly branched polyethylenes have a much lower viscosity compared to linear samples. Slightly branched polyethylenes have got a higher steady-state compliance in comparison to linear products of similar polydispersity, whereas the highly branched polyethylenes of broad molecular mass distribution exhibit a surprisingly low elasticity in comparison to linear polyethylenes of broad molecular mass distribution. In addition sparse levels of long-chain branching cause a different time dependence in comparison to linear polyethylenes. The experimental findings are interpreted by comparison with rheological results from literature on model branched polymers of different molecular topography and chemical composition.

157 citations


Journal ArticleDOI
TL;DR: In this article, the rheological properties of wheat gluten were studied under both small and large deformation and compared with those of the parent flours, and the role of starch in the lower limiting strain of flour doughs was indicated by the exponential decrease in the limiting strain with greater quantities of starch.
Abstract: The rheological properties of wheat gluten were studied under both small and large deformation and compared with those of the parent flours. The limiting strain of linear viscoelastic behaviour of gluten doughs, 3 × 10−2, was an order of magnitude larger than that of the flour doughs, 10−3. The role of starch in the lower limiting strain of flour doughs was indicated by the exponential decrease in the limiting strain of gluten-starch mixtures with greater quantities of starch. Large strain measurements showed gluten doughs possessed greater shear and elongational viscosities than flour doughs and these differences were greatest at lower shear and elongation rates (0.01 and 0.1 s−1). The larger viscosities of flour and gluten doughs at the low strain rates help to stabilise and prevent the collapse of gas bubbles during bread fermentation and baking. Increasing starch levels in gluten-starch mixtures, at either constant or optimal water levels, lowered the elongational viscosity. Dynamic measurements were, however, more sensitive to the level of water added to the gluten-starch mixtures. The storage modulus decreased with increasing starch levels when constant water levels were used to prepare the mixtures, but when optimal water levels were used the storage modulus increased. Gluten and starch are major contributors to the large and small strain rheological properties of flour doughs; however, gluten-starch mixtures were unable to duplicate exactly the rheological properties of flour doughs, indicating that other flour components such as pentosans, lipids and water soluble proteins also influence dough rheology.

144 citations


Journal ArticleDOI
TL;DR: In this paper, the phase separation (binodal) temperature of each blend was determined rheologically using a combination of dynamic frequency and temperature sweeps in parallel plate geometry; it was marked by a change in slope of the elastic modulus and the occurrence of a peak in tan δ in temperature sweeps.
Abstract: We investigated the thermo- rheological behavior of high glass transition, high molecular weight and small dynamic asymmetry blends of poly(styrene-co-maleic anhydride) (SMA) and poly (methyl methacrylate) (PMMA) with varying amounts of maleic anhydride (MA) content, namely 8 wt%, 14 wt% and 32 wt%, in the SMA component. The phase separation (binodal) temperature of each blend was determined rheologically using a combination of dynamic frequency and temperature sweeps in parallel plate geometry; it was marked by a change in slope of the elastic modulus and the occurrence of a peak in tan δ in temperature sweeps. Failure of the time-temperature superposition principle and observation of two peaks in the Cole-Cole plots corroborated these findings. The blends displayed lower critical solution temperature (LCST) behavior with the critical temperatures exhibiting a non-monotonic dependence on the MA content. From rheological and thermal measurements it was concluded that SMA/PMMA blends containing 14% MA were more miscible than those containing 8% or 32% MA, a finding attributed to the compositional dependence of the interplay between SMA-SMA and SMA-PMMA interactions in the different samples. MA also influenced the dynamic asymmetry and pretransitional concentration fluctuations. The phase diagrams corresponding to each blend were modeled using a two-parameter temperature dependent interaction parameter, based on the concept of generalized Gibbs free energy of mixing. The fitted values of interaction parameter were in good agreement with values calculated explicitly using the Flory-Huggins theory.

123 citations


Journal ArticleDOI
TL;DR: In this article, the results from a series of rheological tests of fresh pig kidney have been reported, using a standard strain-controlled rheometer, the oscillation strain sweep experiment showed a linear viscoelastic strain limit of the order of 0.2% and 0.02 s rise time.
Abstract: In this paper, the results from a series of rheological tests of fresh pig kidney have been reported. Using a standard strain-controlled rheometer, the oscillation strain sweep experiment showed a linear viscoelastic strain limit of the order of 0.2% strain. To determine the components of dynamic moduli in terms of frequency, shear oscillation tests were done at strain 0.2% using a stress-controlled rheometer. Shear stress relaxation tests were carried out with a fixed strain of 0.2% and 0.02 s rise time. The model we have developed uses a multi-mode upper convected Maxwell (UCM) model with variable viscosities and time constants, to which we have added a Mooney hyper-elastic response, both multiplied by a damping function. Different forms of damping functions that control the non-linearity of strain-stress profile have been tested. The model was fitted to our experimental data, and matched the entire test data reasonably well with a single set of parameters.

119 citations


Journal ArticleDOI
TL;DR: In this article, a non-monotonic shear flow of a viscoelastic equimolar aqueous surfactant solution (cetylpyridinium chloride-sodium salicylate) is investigated rheologically and optically in a transparent strain-controlled Taylor Couette flow cell.
Abstract: The non-monotonic shear flow of a viscoelastic equimolar aqueous surfactant solution (cetylpyridinium chloride-sodium salicylate) is investigated rheologically and optically in a transparent strain-controlled Taylor Couette flow cell. As reported before, this particular wormlike micellar solution exhibits first a shear thinning and then a pronounced shear-thickening behavior. Once this shear-thickening regime is reached, a transient phase separation/shear banding of the solution into turbid and clear ring-like patterns orientated perpendicular to the vorticity axis, i.e., stacked like pancakes, is observed (Wheeler et al. 1998; Fischer 2000). The solution exhibit several unique features as no induction period of the shear induced phase, no structural build-up at the inner rotating cylinder, jumping pancake structure of clear and turbid ringlike phases, and oscillating shear stresses appear once the pancake structure is present. According to our analysis this flow phenomenon is not purely a mechanical or rheological driven hydrodynamic instability but one has to take into account structural changes of the oriented micellar aggregates (flow induced non-equilibrium phase transition) as proposed by several authors. Although this particular flow behavior and the underlying mixture of shear induced phases and mechanical instabilities is not fully understood yet, some classification characteristics based on a recent theoretical approach by Schmitt et al. (1995) and Porte et al. (1997) where a strong coupling between the flow instability (non-homogeneous flow profile due to the bands) and the structural changes causes the observed transient phenomena can be derived. In reference to the presented model the observed orientation of the rings is typical for complex fluids that undergo a spinodal phase separation coupled with a thermodynamic flow instability. In contrast to other shear banding phenomena, this one is observed in parallel plate, cone-plate, and Couette flow cell as well as under controlled stress and controlled rate conditions. Therefore, it adds an additional aspect to the present discussion on shear banding phenomena, i.e., the coupling of hydrodynamics and phase transition of rheological complex fluids.

99 citations


Journal ArticleDOI
TL;DR: In this paper, the shear orientation of viscoelastic clay-polymer solutions was investigated by means of rheology and flow birefringence (Δn).
Abstract: The shear orientation of viscoelastic clay-polymer solutions was investigated by means of rheology and flow birefringence (Δn). The polymer chains are in dynamic adsorption/desorption equilibrium with the clay particles to form a “network”. The elastic behavior of the network was characterized by constant stress, oscillatory shear, and stress relaxation experiments. Constant stress experiments indicated a yield stress upon which shear flow started and no strain recovery could be observed. Oscillatory shear experiments showed a broad elastic region followed by flow when a critical strain was reached. Stress relaxation experiments showed several relaxation times when the same critical strain was reached. Experiments under steady flow characterized the transient behavior of the network. With increasing steady shear rate a pronounced minimum in birefringence was observed at a critical shear rate. The shear rate dependent viscosity showed near power law behavior and no corresponding critical feature. While birefringence detects orientational effects on a microscopic length scale, rheology averages over macroscopic changes in the sample. The same degree of orientation could be achieved under constant shear rate or constant stress conditions.

92 citations


Book ChapterDOI
TL;DR: In this article, the first and second normal stress difference of viscoelastic suspensions are investigated for all suspensions and N 2 in comparison to N is of special interest for the first normal stress differences.
Abstract: Normal stresses in viscoelastic suspensions may have similar amounts as the shear stresses. So the first and second normal stress difference of such materials are of high interest. Especially the second normal stress differences are unknown for all suspensions. To investigate N 2 in comparison to N is of special interest.

88 citations


Journal ArticleDOI
TL;DR: The transition from solid-like to liquid-like behavior of suspensions of monodisperse spherical particles in a Newtonian continuous phase with varying solid volume concentrations and particle sizes was investigated in rotational shear flows as discussed by the authors.
Abstract: The transition from solid-like to liquid-like behavior of suspensions of monodisperse spherical particles in a Newtonian continuous phase with varying solid volume concentrations and particle sizes was investigated in rotational shear flows It was found that the solid-liquid transition takes place in a relatively narrow shear stress range, where the corresponding shear strain γ and the shear rate $$ \dot \gamma $$ , respectively, increase over some orders of magnitudes Below the transition region the material behaves like a nonlinear elastic solid with an initial linear range, ie, $$ \gamma = f\left( \sigma \right) $$ The transition depends on the type of the shear loading and on the solid volume concentration At high shear rates a nonlinear viscous behavior ( $$ \dot \gamma = f\left( \sigma \right) $$ ) with a terminal Newtonian range $$ \dot \gamma = {\sigma \mathord{\left/ {\vphantom {\sigma \eta }} \right \kern- ulldelimiterspace} \eta } $$ was observed, if the solid volume concentration is below a critical value Above this value the material behaves like a moist bulk solid material

83 citations


Journal ArticleDOI
TL;DR: In this paper, the authors focused on the rheological properties of two-phase polymer blends in the phase inversion region and proposed a new simple equation for the prediction of φPI-values.
Abstract: The present work is focused on the rheological properties of two-phase polymer blends in the phase inversion region. A large number of PS/PMMA- and PSAN/PMMA-blends has been investigated in order to establish a rheological criterion which allows the quantitative determination of the phase inversion concentration φPI by rheological means. Three rheological criteria based on the viscous and elastic blend properties such as maximum of dynamic viscosity η′, slope of G′, and maximum of G′ at a constant evaluation frequency have been tested. By correlating the rheological results to data from quantitative morphological analysis we could prove that the chosen rheological criteria are differently suitable for the determination of φPI. It has turned out that the G′ criterion is the most robust and most suitable one yielding an excellent correlation with morphological data. Based on these findings we propose a new simple equation for the prediction of φPI-values.

75 citations


Journal ArticleDOI
Thomas Schweizer1
TL;DR: In this paper, the authors measured the time dependent first (N1) and second (N2) normal stress difference in a PS 158K melt at 190°C, and found that the edge fracture was delayed to larger samples.
Abstract: Step shear rate experiments in the range of $$0.1 < \dot \gamma < 30s^{ - 1} $$ (0.14 10s^{ - 1} $$ the steady state value of –N2/N1 becomes larger if smaller cone angles are used. Data for α=0.148 rad showed a better coincidence with the linear viscoelastic predictions of viscosity η and first normal stress coefficient $$\psi _1 = N_1 /\dot \gamma ^2 $$ compared to smaller cones.

Journal ArticleDOI
TL;DR: The dynamic flow behavior of polyamide-6 and a nanocomposite based on it was studied in this article, where the two materials were blended in proportions of 0, 25, 50, 75, and 100 wt% PNC.
Abstract: The dynamic flow behavior of polyamide-6 (PA-6) and a nanocomposite (PNC) based on it was studied. The latter resin contained 2 wt% of organoclay. The two materials were blended in proportions of 0, 25, 50, 75, and 100 wt% PNC. The dynamic shear rheological properties of well-dried specimens were measured under N2 at T=240 °C, frequency ω=0.1–100 rad/s, and strains γ=10 and 40%. At constant T, γ, and ω the time sweeps resulted in significant increases of the shear moduli. The γ and ω scans showed a complex rheological behavior of all clay-containing specimens. At γ=10% the linear viscoelasticity was observed for all compositions only at ω>1 rad/s, while at γ=40% only for 0 and 25 wt% of PNC. However, the effect was moderate, namely decreasing G′ and G′′ (at ω=6.28 rad/s; γ=50%) by 15 and 7.5%, respectively. For compositions containing >25 wt% PNC two types of non-linearity were detected. At ω≤ωc=1.4 ± 0.2 rad/s yield stress provided evidence of a 3-D structure. At ω > ωc, G′ and G′′ were sensitive to shear history – the effect was reversible. From the frequency scans at ω > ωc the zero-shear relative viscosity vs concentration plot was constructed. The initial slope gave the intrinsic viscosity from which the aspect ratio of organoclay particles, p=287 ± 9 was calculated, in agreement with the value calculated from the reduced permeability data, p=286.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the time dependence of the sample thickness h(t) for various soft solid materials squeezed between two parallel glass plates by a constant squeezing force F applied at t = 0.
Abstract: Experiments are described in which the time-dependence of the sample thickness h(t) was measured for various soft solid materials squeezed between two parallel glass plates by a constant squeezing force F applied at t=0. A yield stress for each material was also measured using rotational vane and serrated parallel-plate tools. Initially, the squeeze-rate V(t)=–dh/dt of all materials was fast and resembled that of a viscous fluid. Later, most materials showed a very small squeeze-rate, and h seemed to approach a finite plate-separation limit, characteristic of a yield-stress material. For some materials h appeared not to approach a finite limit, attributed to creep or thixotropy not evident in the more rapid vane and serrated parallel-plate measurements. Expressions which relate F to h(t) and V(t) for a Herschel-Bulkley material with stick or slip at the sample-plate interface were reviewed. No materials made frictionless contact with the sample-plate interfaces, and most were best-described by the Herschel-Bulkley squeeze-flow model of Sherwood and Durban (1998). The squeeze-flow data at very low shear rate did not support the existence of Newtonian high viscosity plateaux. A soft solid of closely-packed water-swollen particles swelled when F was decreased after a period of squeeze flow, suggesting relative motion between the constituent phases. The advantages and problems of using squeeze flow as a rheometrical technique are described and discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls and analyze the typical structures of these cross-linked films using Brewster-angle microscopy.
Abstract: The synthesis of microcapsules for technical, cosmetic, and pharmaceutical purposes has attracted much interest in recent years. The design of new capsules requires profound knowledge of their mechanical properties. Rheological studies provide interesting information on intrinsic membrane features and they can also be used to obtain information on bursting processes and shear-induced release of encapsulated compounds. In this article we shall discuss the basic rheological properties of different types of ultra-thin membranes, which can be used to form stable capsules walls. We have also analyzed the typical structures of these cross-linked films using Brewster-angle microscopy. Tiny oil or water droplets, which are surrounded by ultra-thin membranes, form simple types of microcapsules. In addition to the interface shear rheology, we have measured the Young's modulus (elongational modulus) and the Poisson ratio using a modified spinning drop apparatus. The shear-induced deformation and orientation of microcapsules was investigated in optical rheometers (rheoscopes). In the regime of small deformations the results were in fairly good agreement with a theoretical model recently proposed by Barthes-Biesel. Due to the simple synthesis and well-defined structure, microcapsules can also serve as model systems to understand the complicated flow properties of red blood cells (erythrocytes).

Journal ArticleDOI
TL;DR: In this article, the authors studied the rheological expression of the electric field-induced transition in a suspension of monodisperse silica in PDMS as model ERS.
Abstract: Electro-rheological suspensions (ERS) are known to undergo liquid-to-solid transition under the application of an electric field. Long-range interaction between neighboring particles results in sample-spanning particulate structures which behave as soft solids. Here, we studied the rheological expression of this field-induced transition which has many similarities with chemical gelation. This similarity shows in mechanical spectroscopy on a suspension of monodisperse silica in PDMS as model ERS. Upon application of the electric field, dynamic moduli G′, G′′ grow by orders of magnitude and evolve in a pattern which is otherwise typical for gelation of network polymers (random chemical or physical gelation). At the gel point, the slow dynamics is governed by power-law relaxation behavior (frequency-independent tan δ). A low field strength is sufficient to reach the gel point and, correspondingly, the percolating particle structure at the gel point is still very fragile. It can be broken by the imposition of low stress. For inducing a finite yield stress, the field strength needs to be increased further until the long-range electrostatic interaction generates string-like particle alignments which become clearly visible under the optical microscope. The onset of fragile connectivity was defined experimentally by the tan δ method. The ERS was probed dynamically at low frequencies where the transition is most pronounced, and also in steady shear where the rate of structure formation equals the rate of internal breaking.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the performance of a squeeze flow rheometer for determining the viscosity of a highly viscous filled viscoplastic fluid which is representative of the behavior of some propellants.
Abstract: This paper is concerned with the evaluation of a squeeze flow rheometer for determining the viscosity of a highly viscous filled viscoplastic fluid which is representative of the behavior of some propellants. Ordinarily materials of this nature are difficult to characterize using conventional capillary and rotary rheometers because of melt and edge fracture. A model system was chosen because its viscosity could still be measured up to reasonable shear rates of about 1 s−1 in a parallel disk rheometer. The power-law, Bingham, and Herschel-Bulkley empiricisms of the generalized Newtonian fluid were fitted to the steady shear viscosity data. The lubrication approximation was then used to predict the squeezing force as a function of gap height and the results compared to experimentally determined values. The best results were obtained for the Herschel-Bulkley model and in this case the lubrication approximation predictions were on the average some 20% lower than the experimental values between gap to radius ratios of 0.15 and 0.35. A finite element simulation of squeezing flow was carried out to assess the limitations of the lubrication approximation. The numerical solution was found to give a good description of the squeezing force for gap to radius ratios between 0.18 and 0.35. It was estimated that the error involved in the lubrication approximation was about 25% at a gap to radius ratio of 0.3 and decreased to below 2% at a gap to radius ratio of 0.05 for the material studied. Experiments were carried out to assess the effect of slip on the squeezing flow measurements using both roughened and lubricated plates. It was found that no significant slip occurred at squeezing speeds up to about 2.4 mm/s. Lubrication was found to reduce the squeezing force by an order of magnitude.

Journal ArticleDOI
TL;DR: In this paper, the balance equations used for that purpose are based on a Cahn-Hilliard equation for the local concentration, the continuity equation, and a modified Navier-Stokes equation for local velocity, and the essential material and processing parameters such as surface tension, viscosity and volume fraction of both polymers, and imposed shear rate are taken into consideration as model coefficients.
Abstract: The material properties of heterogeneous polymer blends are crucially influenced by their morphology, i.e., by the spatial structure of the blend components and by the specific configuration of the interfaces separating the phases. Hence, in order to understand the behavior of experimentally obtained morphologies, one is interested in modeling the relevant dynamics of the morphology subject to external flow. Thus one can study, e.g., through the interfacial stress tensor the rheological properties due to the interfaces. The balance equations used for that purpose are based on a Cahn-Hilliard equation for the local concentration, the continuity equation, and a modified Navier-Stokes equation for the local velocity. The essential material and processing parameters such as surface tension, viscosity and volume fraction of both polymers, and imposed shear rate are taken into consideration as model coefficients. By regarding hydrodynamic interaction, which is proved to be important in case of immiscible blends, the interfacial relaxation is described properly. Simulations in both three and two dimensions agree at least qualitatively with experimental results concerning droplet deformation, droplet coalescence, and interfacial rheological properties of the blend.

Journal ArticleDOI
TL;DR: The analysis derived by Bloksma (1957) was also used to calculate stress and strain at the top of the inflated bubble from gauge pressure and bubble volume data as mentioned in this paper.
Abstract: The bubble inflation test has been used to determine the equi-biaxial stress-strain curve of flour/water dough. This was achieved by undertaking experimental measurements of strain, wall thickness and radius of curvature at the top of the bubble as well as applied pressure. It was observed that the bubble was spherical initially but changed to an elliptical shape at large strains. The analysis derived by Bloksma (1957) was also used to calculate stress and strain at the top of the inflated bubble from gauge pressure and bubble volume data. It was found that the analysis led to accurate bubble heights at moderate strains only, a consequence of the non-spherical bubble shape. In addition, at the top of the bubble, the analytical strain was larger and the thickness was much smaller than the experimental values. The bubble wall thickness distribution was more uniform than the analytical predictions. The discrepancies in bubble height, radius of curvature, strain and thickness had a major effect in the analytical stress-strain curve, as both stress and strain were overestimated, the stress being in error by a factor of four at large strains. Therefore, it is concluded that when the bubble inflation test is used, it is necessary that experimental readings of strain, thickness and radius of curvature as well as pressure should be made to ensure accurate stress-strain curves.

Journal ArticleDOI
TL;DR: In this article, a new process model is introduced which assumes that the elongational viscosity in the RME Rheometrics test is a function of the draw ratio only.
Abstract: Several linear (LLDPE, HDPE, PS) and long-chain-branched (LDPE, PP) polymer melts were investigated by an elongational rheometer (RME Rheometrics) and by Rheotens (Gottfert). The Molecular Stress Function (MSF) theory is briefly reviewed and used to extrapolate the steady-state elongational viscosity. To evaluate Rheotens experiments, a new process model is introduced which assumes that the elongational viscosity in the Rheotens test is a function of the draw ratio only. The apparent elongational viscosities extracted from Rheotens curves are found to lie in between the steady-state elongational viscosity and three times the shear viscosity.

Journal ArticleDOI
TL;DR: Fourier transform mechanical spectroscopy technique (FTMS) is utilized as a powerful tool to study the sol-gel transition of covalent bonded polymeric network Winter and Chambon criteria resulting from the fractal-geometry characteristic of the gel networks are used to determine the gel point with only single experiment using this technique as discussed by the authors.
Abstract: Fourier transform mechanical spectroscopy technique (FTMS) is utilized as a powerful tool to study the sol-gel transition of covalent bonded polymeric network Winter and Chambon criteria resulting from the fractal-geometry characteristic of the gel networks allow the determination of the gel point with only single experiment using this technique The gelation behaviors of low melt viscosity ternary systems of benzoxazine, epoxy, and phenolic resins are investigated and analyzed by the technique in order to study the effect of epoxy diluent on the rheological property development before and after the gel points The gel time at 140 °C ranges from 5 min to 30 min and less than 5 min at 180 °C for all tested ternary system compositions The gelation of the ternary mixture shows an Arrhenius-type behavior and the gel time can be well-predicted by the Arrhenius equation

Journal ArticleDOI
TL;DR: In this article, a rotary-mode piezoelectric instrument was proposed to measure linear viscoelasticity of shear viscosity up to f = 50 Hz (ω=300 s−1).
Abstract: Conventional, motor controlled rheometers, allow, e.g., stress-controlled measurements of the shear viscosity up to several thousands in shear rate, but reliable oscillating viscoelastic measurements only up to f=50 Hz (ω=300 s–1). This limitation is overcome – even if only for linear viscoelasticity – by a new piezoelectric instrument oscillating in rotary mode (PRV), covering the frequency range from 0.5 Hz up to 2 kHz , and bridging the gap to resonator methods.

Journal ArticleDOI
TL;DR: In this article, a rotational rheometer equipped with an electronically commutated motor (EC-motor) allows one to conduct stress and strain experiments with the same Rheometer in rotational mode.
Abstract: As shown previously, a rotational rheometer equipped with an electronically commutated motor (EC-motor) allows one to conduct stress and strain experiments with the same rheometer in rotational mode. A new method has now been developed to improve further strain controlled oscillatory measurements by adjusting the strain directly within a single oscillation cycle.

Journal ArticleDOI
TL;DR: The effect of mixing particles of different sizes on the electrorheological response of suspensions under steady shear flow was investigated in this article, where two sizes, 15 μm and 50 μm, of monodisperse spherical sulfonated poly(styrene-co-divinylbenzene) particles were used.
Abstract: The effect of mixing particles of different sizes on the electrorheological response of suspensions under steady shear flow was investigated. Two sizes, 15 μm and 50 μm, of monodisperse spherical sulfonated poly(styrene-co-divinylbenzene) particles were used. Several electrorheological fluids were made containing different proportions of small and large particles dispersed in silicone oil, but with constant overall particulate concentration. It was found that the mixed size system produced the highest electrorheological response under the shear rates used (10 s−1 to 500 s−1), which is the opposite trend to previous studies of bimodal systems with larger size ratios.

Journal ArticleDOI
TL;DR: In this article, a selection of four commercial flours has been subjected to extensive rheological measurements as part of a comprehensive program of wheat improvement, and the results have been used to determine which of the many types of measurements provided significant discrimination between various types of modern baker's flours (including biscuit flours).
Abstract: A selection of four commercial flours has been subjected to extensive rheological measurements as part of a comprehensive program of wheat improvement. The results have been used to determine which of the many types of rheological measurements provide significant discrimination between various types of modern baker's flours (including biscuit flours) and to procure data suitable for use in mathematical models describing the dough rheology. The rheological measurements undertaken include oscillatory shear at low amplitude, steady shear at a low shear rate, stress relaxation and extensional viscosity testing. Although oscillatory shear data show minor differences between these flours, the other tests show significant variations and these provide very good discrimination between the different flour types in comparison with conventional dough testing (e.g. by the extensograph). The current dough rheological measurements provide further insight into molecular structure. In the future, mathematical (constitutive) models are expected to provide a means of predicting processing and baking behaviour of bread dough.

Journal ArticleDOI
TL;DR: In this article, a large disagreement was found between the stress-strain curve based on experimental data and the curve derived from Bloksma's analytical model, and it was further concluded that the accuracy of the analysis was dependent on the material properties.
Abstract: In Part I the bubble inflation test was used to measure the stress-strain relationship of dough. A large disagreement was found between the stress-strain curve based on experimental data and the curve derived from Bloksma's analytical model. In Part II, a numerical simulation of the bubble inflation test is performed using Finite Element Analysis, in order to obtain further information regarding the accuracy of the analytical predictions. A hyperelastic model is assumed for the dough, with a strain energy potential described by the compressible form of the Mooney-Rivlin model. Four cases were investigated, corresponding to various combinations of material parameters of the Mooney-Rivlin model. The numerical results reinforce the conclusions drawn in Part I of the study, specifically that Bloksma's analysis of the bubble inflation could lead to large errors in the stress-strain curve. It was further concluded that the accuracy of the analysis was dependent on the material properties. For a neo-Hookeian material, the analysis leads to accurate results. This is because, for this material, all the assumptions made in the analysis regarding the bubble shape, the material's incompressibility and the bubble wall thickness distribution are accurate.

Journal ArticleDOI
TL;DR: In this paper, the extrusion behavior of PTFE pastes in a ram extruder was investigated using 1H-NMR imaging (MRI) and 19F-MRI.
Abstract: Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The 19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by means of correlation techniques without any preparation or marking of the pastes.

Journal ArticleDOI
TL;DR: In this paper, nonlinear hydrodynamic equations for polymeric fluids with permanent or transient orientational order are discussed and a comparison with existing phenomenological and mesoscopic models is given.
Abstract: Nonlinear hydrodynamic equations for polymeric fluids with permanent or transient orientational order are discussed. We start from a description that utilizes the well-known nematohydrodynamic equations for low molecular weight uniaxial nematics. We concentrate on the reversible nonlinearities in the dynamic equation for the orientational tensor order parameter. The non-phenomenological part is unambiguously of the 'corotationally convected' or 'Jaumann' type. This holds also for the case of transient orientational order, which occurs in semi-flexible or rigid polymeric systems in the isotropic phase. The phenomenological part of the (nonlinear) reversible dynamics (flow alignment) is different for the isotropic and uniaxial case (the biaxial case is discussed in an Appendix). The corresponding form of the stress tensor is discussed. A comparison with existing phenomenological and mesoscopic models is given.

Journal ArticleDOI
TL;DR: In this article, a large collection of experimental difficulties associated with the measurement of uniaxial extensional properties of polymer melts in the Rheometrics RME extensional rheometer is described.
Abstract: In a recent paper by T. Schweizer (Schweizer 2000) a large collection of experimental difficulties associated with the measurement of uniaxial extensional properties of polymer melts in the Rheometrics RME extensional rheometer is described. The work covers topics such as sample preparation for different types of polymers (sensitive or not to moisture) supplied in different shapes (pellets or powder), the necessary corrections to the tensile force, and the ever-present problem of determining the true strain rates of the experiments. The aim of the present paper is to complement and expand the work of Schweizer by pointing out other experimental problems that are the cause of errors in extensional rheometry of polymer melts. The present analysis, however, is not exclusively dedicated to the RME, unlike that of Schweizer, being directed instead to a general class of apparatus that work according to the principle of stretching a constant length sample between pairs of counter-rotating rollers; for example, all the data shown was obtained with our own extensional rheometer (Maia et al. 1999). This work will focus on the importance of the correct choice of the supporting media used for sample heating and support, the importance of end-effects, and the influence that the griping surfaces can have in such measurements.

Journal ArticleDOI
TL;DR: In this article, the authors presented a study of coalescence of polymer droplets in the viscosity ratio range (p) going from 0.1 to 10.5.
Abstract: The study of coalescence of polymer droplets is presented in the viscosity ratio range (p) going from 0.1 to 10. It is shown that the determination of the characteristic time of coalescence is a good way to estimate the interfacial tension. Polydimethylsiloxane (PDMS) is mixed with polyisobutylene (PIB) and the temperature change provides a way to modify the interfacial tension of the PDMS/PIB system significantly, as measured using a pendant drop apparatus. We obtain a dependence of the reduced coalescence time as a function of p–1/2 which gives access to the interfacial tension. This technique can be an interesting choice for estimating interfacial tension without requiring sophisticated techniques. In a further attempt to correlate these observations with a theoretical model (Verdier C (2001) Polymer 42), the flow field inside and outside the droplets is investigated. PIV measurements are carried out where the evidence of elongational regimes is demonstrated. Such experiments are also interesting for future comparisons with numerical results.

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TL;DR: In this paper, the pressure dependence of the viscosity of aqueous solutions of different sugars was investigated with a gravity driven high pressure viscometer with a maximum pressure of 700 MPa.
Abstract: New experimental data for the pressure dependence of the viscosity of aqueous solutions of different sugars are presented. Measurements were carried out with a gravity driven high pressure viscometer with a maximum pressure of 700 MPa. The influence of both concentration and temperature on the pressure dependence of the viscosity is considered. Next to the data, a viscosity model based on a suspension model is introduced and it is shown that it is able to predict the viscosity for sugar solutions in a broad parameter range, including pressure. It is demonstrated that the relative viscosity for varying sugar mass fraction at constant pressure coincides with the pressure-dependent relative viscosity for a fixed sugar mass fraction, suggesting that there are no structural changes occurring under pressure. A brief interpretation of the viscosity model is given.