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Nov 1996

Volume 40, Issue 6, pp. 987-1266


1995 Bingham Medal Address: Oh, thermorheological simplicity, wherefore art thou?

Donald J. Plazek

J. Rheol. 40, 987 (1996); http://dx.doi.org/10.1122/1.550776 (28 pages) | Cited 11 times

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Polyisobutylene (PIB) was the first polymer whose viscoelastic behavior was thoroughly studied. The measurements made worldwide on the PIB sample distributed from the National Bureau of Standards were compiled and analyzed by Bob Marvin. The superposition of the data substantiated the time–temperature reduction process, which was suggested by Herbert Leaderman, first put into practice by Arthur Tobolsky, and given a theoretical foundation by John Ferry. Polymers that behaved in a like manner were called thermorheologically simple by A. J. Staverman and F. Schwarzl. Subsequently the behavior of PIB has been found to be the exception rather than the rule. The various deviations for this simplicity are briefly reviewed and PIB is reexamined. ©1996 Society of Rheology
Show PACS
83.60.St Non-isothermal rheology
83.60.Bc Linear viscoelasticity
83.80.Va Elastomeric polymers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
01.10.Cr Announcements, news, and awards

Tensile stress measurements of dilute polymer solutions containing traces of salts and dyes

Jae K. Lee and Neil S. Berman

J. Rheol. 40, 1015 (1996); http://dx.doi.org/10.1122/1.550771 (11 pages)

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Tensile stress studies were made on dilute solutions of poly(ethylene oxide) and polyacrylamide using a fiber spinning apparatus to investigate the interaction of polymer molecules with the flow field. The addition of dyes or metal ions to the solutions has a considerable influence on the tensile stress. These ingredients normally cause contraction of the polymer coils and stiffen the molecular chains. One additive, Congo Red, markedly increased the tensile stress of poly(ethylene oxide) solutions. ©1996 Society of Rheology
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83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.50.Jf Extensional flow and combined shear and extension

Brownian electrorheological fluids as a model for flocculated dispersions

Yvette Baxter‐Drayton and John F. Brady

J. Rheol. 40, 1027 (1996); http://dx.doi.org/10.1122/1.550772 (30 pages) | Cited 14 times

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The rheological behavior of Brownian electrorheological (ER) fluids is studied as a model for flocculated colloidal dispersions. The ER fluid has the advantages that the interparticle potential energy can be varied by simply changing the applied field strength, and the microstructure consists of essentially linear chains of particles aligned with the field direction. Under simple shear flow, the suspension has a high‐shear‐rate Newtonian viscosity and a shear thinning viscosity at lower shear rates. For moderate attractive potential well depths, Umin/kT, the suspension has a low‐shear viscosity that scales as exp(Umin/kT). Furthermore, the low‐shear limiting behavior is seen at shear rates that scale as exp(−Umin/kT). A theory is proposed that makes use of the time scale of diffusion for aggregated particles out of their mutual potential well, τ∼(a2/D)(kT/Umin)exp(Umin/kT), much in the spirit of the Eyring theory. Here a is the particle radius and D is the diffusivity of an isolated particle. When the shear rate is nondimensionalized by τ, the reduced viscosity data for all field strengths collapse onto a single universal curve. Although we use a relatively small monolayer suspension, our simulation results compare well to the limited experimental and theoretical work on Brownian ER suspensions. The scaling relationship for the low‐shear viscosity has also been evidenced in other studies of flocculated dispersions. ©1996 Society of Rheology
Show PACS
83.80.Gv Electro- and magnetorheological fluids
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
82.70.Dd Colloids
83.50.Ax Steady shear flows, viscometric flow

An experimental study of particle migration in pipe flow of viscoelastic fluids

M. A. Tehrani

J. Rheol. 40, 1057 (1996); http://dx.doi.org/10.1122/1.550773 (21 pages) | Cited 5 times

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This paper reports experiments on particle migration in viscoelastic fluids used in hydraulic fracturing. It is found that particle migration in such fluids is controlled by the elastic properties of the suspending fluid and the shear rate gradient. In fluids with low but measurable normal stresses and dominant shear‐thinning properties, particles migrate to regions of lower shear rate. Migration is fast initially, but slows down rapidly over a short distance. For these fluids the bulk migration velocity correlates with the product of the Weissenberg number and the mean shear rate gradient. In contrast, highly elastic fluids with relaxation times well above one second and shear‐thickening properties at low shear rates, flow with a central plug region or slip at the wall, producing little or no migration. ©1996 Society of Rheology
Show PACS
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.60.Bc Linear viscoelasticity

Influence of molecular weight distribution on the melt extrusion of high density polyethylene (HDPE): Effects of melt relaxation behavior on morphology and orientation in HDPE extruded tubular films

Ta‐Hua Yu and Garth L. Wilkes

J. Rheol. 40, 1079 (1996); http://dx.doi.org/10.1122/1.550801 (15 pages) | Cited 1 time

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The influence of molecular weight distribution and extrusion processing variables on the morphological features and orientation of high density polyethylene (HDPE) uniaxially extruded tubular films was investigated. In order to gain a better understanding of the orientation–crystallization behavior occurring during extrusion processing, the melt flow properties of the two HDPE resins with identical M̄n (14 600) values but different molecular weight distributions (M̄w/M̄n=10.3, 15.1), utilized in our previous study, were characterized by dynamic rheological experiments over the temperature range from 150 °C to 230 °C within the angular frequency range from 0.1 to 100 rad/s. The experimental data were shifted to produce master flow curves. The flow activation energy calculated from the shifting process was found to be 25.9 kJ/mol for resin 1 and 29.1 kJ/mol for resin 2. The characteristic relaxation time at 190 °C obtained by use of a Carreau–Yasuda analysis for resin 2 having the broader molecular weight distribution was found to be 6.5 times greater than that of resin 1. This observation further supports our previous conjecture that the prominence of the fibril nuclei in resin 2 is due to its longer melt relaxation time behavior. The extrusion processing variables of melt temperature at the die exit, quench height (which is the distance from the exit of the die to the cooling ring), flow rate of the air through the cooling ring, film line speed, and die gap were varied to control the melt relaxation time of HDPE resins and the processing time frame for cooling. The results show that a longer melt relaxation time and a shorter cooling processing time can enhance the formation of fibril nuclei. The importance of melt relaxation behavior in influencing the final morphological structure in HDPE extruded films and their associated properties is clearly made evident in this paper. ©1996 Society of Rheology
Show PACS
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
68.55.-a Thin film structure and morphology
83.50.-v Deformation and flow

Kinetics of structure development in liquid–liquid dispersions under simple shear flow. Theory

S. A. Patlazhan and J. T. Lindt

J. Rheol. 40, 1095 (1996); http://dx.doi.org/10.1122/1.550774 (19 pages) | Cited 2 times

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The kinetics of structure development in a moderately concentrated liquid–liquid dispersion under the hydrodynamic conditions of simple shear flow has been analyzed using differential population balance equations. The existing models of the breakup and coalescence phenomena have been examined, modified, and included in the population balances to the extent necessary. It was found that in the present range of drop sizes and viscosity ratios the temporal evolution of the average drop size is primarily determined by drop breakup rather than by coalescence. It was further shown that the evolution of the size distribution function as well as the average drop size are strong functions of the viscosity ratio, exhibiting sharp changes at the critical capillary number. The role of the initial drop size distribution on the time‐dependent state of the dispersion was examined, including the path leading to a bimodal distribution. ©1996 Society of Rheology
Show PACS
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.50.Ax Steady shear flows, viscometric flow
47.55.D- Drops and bubbles

Nuclear magnetic resonance imaging of apparent slip effects in xanthan solutions

Craig J. Rofe, Lourdes de Vargas, José Perez‐González, Rodney K. Lambert, and Paul T. Callaghan

J. Rheol. 40, 1115 (1996); http://dx.doi.org/10.1122/1.550775 (14 pages) | Cited 4 times

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Nuclear magnetic resonance imaging has been used to investigate the flow of 0.2% aqueous solutions of xanthan gum. Apparent slip was observed in solutions made from the material supplied by UNAM but not in that supplied by Aldrich or Kelco. The apparent slip velocity was a constant fraction of the maximal velocity for a given contraction ratio. The apparent slip velocity also appeared to be independent of L/D but was strongly influenced by the wall stress, the observed apparent slip velocities being comparable with those determined using the Mooney analysis on capillary flows. After exposure to the action of a syringe pump, which reduced the mean molecular weight of the xanthan, the UNAM xanthan solution no longer exhibited apparent slip. Slip appears to be a function of molecular weight, possibly through sensitivity to the aspect ratio of the molecule. ©1996 Society of Rheology
Show PACS
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.50.Lh Slip boundary effects (interfacial and free surface flows)
76.60.Pc NMR imaging

Crossover behavior in the viscosity of semiflexible polymers: Intermolecular interactions as a function of concentration and molecular weight

G. C. Berry

J. Rheol. 40, 1129 (1996); http://dx.doi.org/10.1122/1.550777 (26 pages) | Cited 1 time

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A simple relation is presented for the viscosity of isotropic solutions of flexible, semiflexible and rodlike chains over a range of concentration from dilute solutions to undiluted polymer, chain contour length L and persistence length â. The expression is designed to account for the separate effects of screening of thermodynamic and hydrodynamic interactions, and the onset of intermolecular chain entanglements under Flory theta solvent conditions, or in ‘‘good’’ solvents, for which intramolecular excluded volume is important in dilute solutions. The relation includes a revised (dimensionless) Fox parameter X̃c that determines the onset of intermolecular entanglements, where X̃c=πNAρLcâ/3ML for semiflexible polymers with â≪L, with ρ the polymer density, ML the mass per unit length of the chain, and Lc the value of L for the onset of entanglement effects in undiluted polymer; X̃c≊100 for a number of systems, including rodlike chains. ©1996 Society of Rheology
Show PACS
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
47.50.-d Non-Newtonian fluid flows
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics

Crossover behavior in the viscosity of semiflexible polymers: Solutions of sodium hyaluronate as a function of concentration, molecular weight, and temperature

M. Milas, I. Roure, and G. C. Berry

J. Rheol. 40, 1155 (1996); http://dx.doi.org/10.1122/1.550778 (12 pages) | Cited 1 time

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Viscometric data on moderately concentrated solutions of the semiflexible macromolecule sodium hyaluronate over a range of molecular weight M and solute concentration c in aqueous 0.1M NaCl are analyzed using a generalized expression for the viscosity of isotropic polymers and their solutions. Owing to its semiflexible nature, the effects of excluded volume interactions are effectively screened for sodium hyaluronate under the conditions studied, and intramolecular hydrodynamic interactions are largely screened, even at infinite dilution. The consequences of this for scaling of the viscosity relative of solutions of sodium hyaluronate with the parameters c[η] and cM is discussed. The dependence of the viscosity on cM is in accord with the generalized relation, and leads to an estimate for the persistence length in reasonable accord with that found by light scattering measurements on dilute solutions. The temperature dependence of the viscosity suggests that the dependence of the persistence length on temperature may be partially suppressed with increasing polymer concentration. ©1996 Society of Rheology
Show PACS
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics

Quasistatic measurements on a magnetorheological fluid

Xinlu Tang and Hans Conrad

J. Rheol. 40, 1167 (1996); http://dx.doi.org/10.1122/1.550779 (12 pages) | Cited 4 times

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The shear stress τ–shear strain γ behavior of suspensions of carbonyl iron particles in silicone oil was determined at a shear rate γ̇=0.042 s−1 as a function of applied magnetic induction B0 (0.5–6.0 kG), volume fraction of particles ϕ(0.05–0.30), and roughness of the shearing surfaces. At low fields, the steady‐state shear stress τS was significantly higher for a roughened surface compared to a smooth surface, but became only slightly dependent on roughness at high fields. In accord with theoretical considerations, the ratio τS/ϕ was proportional to the square of the calculated magnetic field H0 inside the suspension at low fields, but its dependence on H0 became smaller as the field increased. The smaller dependence may result from the magnetic saturation of the particles or the slipping boundary condition. ©1996 Society of Rheology
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83.80.Gv Electro- and magnetorheological fluids
83.50.Ax Steady shear flows, viscometric flow

A fifty cent rheometer for yield stress measurement

N. Pashias, D. V. Boger, J. Summers, and D. J. Glenister

J. Rheol. 40, 1179 (1996); http://dx.doi.org/10.1122/1.550780 (11 pages) | Cited 12 times

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The slump test, initially developed to determine the flow properties of fresh concrete, has been adopted as a means of accurately measuring the yield stress of strongly flocculated suspensions. The slump test offers a quick and easy way of measuring yield stress without the need for sophisticated electronic equipment, thereby giving plant operators an effective tool for determining yield stress. The model used to predict the yield stress from the conical slump test was devised by Murata (1984) and corrected by Christensen (1991). In the present case the theory has been adapted for a cylindrical geometry. Yield stress measurements obtained with the vane for numerous mineral suspensions under known surface chemistry conditions are compared to the slump measurements and theoretical prediction. Good agreement is obtained. ©1996 Society of Rheology
Show PACS
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.60.La Viscoplasticity; yield stress
83.85.Cg Rheological measurements—rheometry

Rheological behavior of highly concentrated aqueous silica suspensions in the presence of sodium nitrate and polyethylene oxide

A. A. Zaman, B. M. Moudgil, A. L. Fricke, and H. El‐Shall

J. Rheol. 40, 1191 (1996); http://dx.doi.org/10.1122/1.550781 (20 pages) | Cited 6 times

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The shear flow properties of aqueous silica suspensions at different solids loading in the presence of polyethylene oxide (PEO) and added salt (NaNO3) have been investigated. Particular attention is given to the evaluation of the role of electrolyte concentration, pH, and polymer concentration in viscosity reduction. The variation of the rheological properties with shear rate, solids loading, particle size, pH, electrolyte concentration, PEO concentration, and its molecular weight are discussed. The viscosity of the silica suspension was determined to be a decreasing function of the particle diameter and at 54% volume, the effect of particle size was scaled using Peclet number and relative viscosity of the suspension (hard sphere scaling). The flow properties of silica suspensions are highly affected by the pH of the suspending media and concentration of the added salt. At a fixed electrolyte concentration, the viscosity decreases by increasing pH, reaches a minimum, and then increases with further increase in pH. At a fixed pH level, the same behavior was observed for viscosity as a function of electrolyte concentration. The effect of the electrolyte concentration is more significant at lower shear rates. It is shown that the rheological properties of silica suspensions are strongly affected by the concentration of the added polymer and its molecular weight. For each sample, there is a critical amount of polymer that must be added before low viscosities result. There is a nearly linear relation between the critical polymer concentration and volume fraction of the particles. The results of this work provide useful information for selection of a proper pH range, electrolyte concentration, and optimum polymer concentration to control the viscosity behavior of highly concentrated silica slurries. ©1996 Society of Rheology
Show PACS
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.50.Ax Steady shear flows, viscometric flow
83.85.Jn Viscosity measurements

Rheology of dense suspensions of platelike particles

S. Jogun and C. F. Zukoski

J. Rheol. 40, 1211 (1996); http://dx.doi.org/10.1122/1.550798 (22 pages) | Cited 15 times

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The flow properties of dense kaolin suspensions are explored for volume fractions as large as 0.43. The particles were suspended in phosphate buffers at pHs of 7 and 10 where edge‐face interactions are negligible. These platey particles have an aspect ratio of approximately 12 and, thus, are likely to show alignment at volume fractions above a critical volume fraction ϕ∗=0.10. As the concentration is increased from the dilute region of Newtonian behavior, the suspensions develop a yielding type of response near this critical volume fraction. The time dependence of the recoverable strain in some dense suspensions is found to scale on γ̇0t where t is the time after the stress is released and γ̇0 is the steady shear rate prior to release of the stress. Over the same time period the elastic modulus remains constant. The magnitude of the modulus is, however, dependent on γ0 decreasing from a low shear rate plateau value of Gmax′ to a high shear rate plateau value of Gmin′. The shear rate halfway between Gmax′ and Gmin′ is independent of volume fraction and lies near 0.39 D0rot where D0rot is the free solution rotational diffusion constant of the plates. This behavior is interpreted as indicating that the plates experience a tumbling/shear aligning transition as the shear rate is raised. Further evidence for alignment is found in shear induced changes in suspension conductivity. ©1996 Society of Rheology
Show PACS
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.10.Gr Constitutive relations

Residual normal force after cessation of squeezing flow of liquid crystalline polymers

Alejandro D. Rey

J. Rheol. 40, 1233 (1996); http://dx.doi.org/10.1122/1.550795 (5 pages)

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Classical liquid crystal theories are used to develop a model to compute the normal forces and shear torques for liquid crystalline polymers. The model is applied to the parallel disk geometry and the normal forces from three representative average molecular orientations are computed. It is found that a positive normal force tending to separate the parallel disks will always be present whenever the orientation is subjected to a twisting deformation. For typical parameter values and geometries, the model predicts that normal forces are six orders of magnitude larger than shear torques. The model predictions are validated with the experimental data presented by Langelaan and Gotsis (1996). ©1996 Society of Rheology
Show PACS
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
83.50.-v Deformation and flow
83.10.Gr Constitutive relations
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure

On the effects of a piezoviscous lubricant on the dynamics of a journal bearing

D. Rh. Gwynllyw, A. R. Davies, and T. N. Phillips

J. Rheol. 40, 1239 (1996); http://dx.doi.org/10.1122/1.550782 (28 pages) | Cited 1 time

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A moving spectral element method is used to investigate the effects of non‐Newtonian lubricants on the dynamics of a journal bearing. It is well known that for a constant viscosity full‐film lubricant the journal eventually displays half‐speed whirl that is undesirable due to the accompanying fall in load bearing capacity and vibration. The inclusion of a cavitation model into the scheme stabilizes the motion of the journal in some situations. In this paper it is demonstrated that piezoviscous lubricants can stabilize the journal even without the incorporation of a cavitation model. The addition of a cavitation model is shown to stabilize the motion of the journal further in the sense that equilibrium points or limit cycles are reached more quickly. The effects of shear thinning and inertia on the motion of the journal are also considered. ©1996 Society of Rheology
Show PACS
81.40.Pq Friction, lubrication, and wear
83.50.-v Deformation and flow
47.11.-j Computational methods in fluid dynamics
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