摘要:

We study the time‐dependent compressible flow of a Newtonian fluid in slits using an arbitrary nonlinear slip law relating the shear stress to the velocity at the wall. This slip law exhibits a maximum and a minimum and so does the flow curve. According to one‐dimensional stability analyses, the steady‐state solutions are unstable if the slope of the flow curve is negative. The two‐dimensional flow problem is solved using finite elements for the space discretization and a standard fully implicit scheme for the time discretization. When compressibility is taken into account and the volumetric flow rate at the inlet is in the unstable regime, we obtain self‐sustained oscillations of the pressure drop and of the mass flow rate at the exit, similar to those observed with the stick‐slip instability. The effects of compressibility and of the length of the slit on the amplitude and the frequency of the oscillations are also examined.

ISSN:0148-6055    

DOI:10.1122/1.550479

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

A unifying stress–strain model for physical networks (polymer melts) and for permanent networks (rubbers) is presented. It is based on three assumptions: (1) the uncrossability condition of real chains can be modeled by the tube concept; (2) the tube diameter is a function of the average stretch; and (3) the tube volume is invariant with respect to deformation. The model predicts that stress–strain behavior of dry and swollen rubber networks is completely determined by four material constants: the equilibrium modulusG∞of the bulk network; the critical entanglement modulusG*e, which is equivalent to the plateau modulusGNof the un‐crosslinked parent melt; a finite extensibility parameter α; and a solvent‐polymer interaction exponent β. Predictions are compared with experimental data in elongation, and agreement is excellent. The Mooney–Rivlin constantC2of unswollen networks with high crosslink densities is limited to roughlyGN/2, and the origin of theC2term is shown to be due to nonaffine deformation of the entanglement network. Nonaffine deformation of network strands is caused by an increasing lateral restriction due to neighboring chains, while upon swelling, the nonaffine reduction of the microscopic length scale leads to the vanishingC2value of highly swollen rubbers.

ISSN:0148-6055    

DOI:10.1122/1.550480

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

The influence of the compatibilizer, a block copolymer, on the rheological behavior of polypropylene/polyamide blends is discussed here. A dual‐flow behavior has been observed. At low shear rate, the blend viscosity is higher than the viscosity of the matrix, while at a high shear rate the contrary is observed. The morphology of the blends is different in the two domains, with a nodular morphology at low shear rate and a lamellar structure at high shear rate. The low shear rate behavior has been theoretically analyzed using a two‐phase Oldroyd model. The copolymer has been located at the interface and is supposed to dominate the nodular dispersed‐phase behavior. A good agreement has been found for the low‐concentration blend. A model of lamellar flow gives the right response for the high shear rate regime. The copolymer, acting as a lubricant, has an influence on the blend viscosity and the agreement with experimental data is discussed.

ISSN:0148-6055    

DOI:10.1122/1.550602

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

To examine the scaling relation proposed for textured materials, viscoelastic properties of binary mixtures of immiscible Newtonian fluids were measured in steady shear flows and in the transient states after step changes of the shear rate. The sample was a mixture of silicone oil and resin oil, which have almost equal density and viscosity. It was observed that (i) the shear stress and the first normal stress difference, under the steady shear flows, are almost proportional to the shear rate, and that (ii) the plots of the scaled transient stresses after a step change of shear rate, against the scaled strain, compose a single curve. These results can be well explained by the scaling relation. However, the shape of the transient stress curves after step changes of shear rate do not agree with that predicted by the constitutive equation proposed by Doi and Ohta.

ISSN:0148-6055    

DOI:10.1122/1.550481

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

Relaxation of monodisperse and polydisperse electrorheological (ER) suspensions under linear deformation is investigated. The electrostatic polarization model is employed to describe ER suspensions, and solutions to the equations of motion are obtained by dynamic simulation and regular perturbation methods. Sources of relaxation events are identified by examining partial rheological functions that are defined in the text. Relaxation of both monodisperse and polydisperse suspensions is found to be confined to approximately the same limited range of relaxation times, although polydisperse suspensions may produce relaxation events over a very broad range of relaxation times. Events occurring at large relaxation times arise from relatively weak forces that do not significantly influence the extent of relaxation. Other relaxation mechanisms and potential sources of dispersion broadening are also discussed.

ISSN:0148-6055    

DOI:10.1122/1.550482

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

Structure and molecular mobility of complexes between carboxymethylpolysaccharides (carboxymethylcellulose and carboxymethylchitin) and alkaline‐earth metal ions in aqueous systems were studied by means of dynamic viscoelasticity, SAXS and NMR measurements. The frequency‐dependent curves of the dynamic modulus measured with a cone‐plate rheometer shift to a longer time‐scale region with complex formation and can be superposed to a master curve by only a horizontal shift. This means that the relaxation times lengthen by complexation and that the complexation is an intramolecular rather than an intermolecular process. The SAXS and NMR measurements revealed that the site for complexation is a cavity between the carboxyl group and the hydroxy group attached to the neighboring residue. A new molecular model for complexation was presented.

ISSN:0148-6055    

DOI:10.1122/1.550609

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

Unidirectional carbon fiber (CF)/poly(ether‐ether‐ketone) (PEEK) composite was manufactured from the commingled yarns composed of CF and PEEK filaments (this composite is named ‘‘commingled composite’’). The thermal expansion coefficient (TEC) of the commingled composite was measured and compared with that of CF/PEEK unidirectional composite made of prepreg sheets (this composite is named ‘‘prepreg composite’’). The minimum value of TEC’s parallel to the fiber direction was observed at around 150 °C for both specimens which were not thermally treated. This minimum disappeared after the thermal treatment at 230 °C for 30 min or the repeating measurements (0 °C→230 °C, 0 °C→230 °C,...). While the TEC of the prepreg composite was almost independent of temperature, that of the commingled composite showed a remarkable decrease at temperatures above the glass transition temperature (Tg) of PEEK. This could be interpreted in terms of the orientation distribution of carbon fibers in the commingled composite. The difference of longitudinal TEC’s between heating and cooling experiments was attributable to the temperature difference between the surface and the inner parts of the specimen. The TEC’s transverse to the fiber direction were scarcely influenced by the thermal history. The TEC’s increased slowly below 100 °C and increased rapidly above 100 °C with increasing temperature. Theoretical predictions based on the extended equivalent inclusion method and on the classical lamination theory exhibited good agreement with experimental data. However, it could not be predicted that the TEC’s parallel to the fiber direction were depressed at around 30 °C. The cause of this discrepancy was supposed due to the temperature dependence of TEC’s of the carbon fiber itself.

ISSN:0148-6055    

DOI:10.1122/1.550483

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

Pigment dispersion in acid‐neutralized water soluble acrylic resins which have both acidic and basic functional groups was studied. The dispersibility was evaluated by the gloss and the yield value of the pastes. As for the dispersion of a positively charged pigment, an excellent dispersibility of the pigment was obtained by the resin adsorption through electrostatic interaction between positive charge of the pigment and negative charge of the resins when the acid strength of the resin was higher than that of the neutralizing acid. On the other hand, when the acid strength of the neutralizing acid was higher or a negatively charged pigment was used, no effect on the introduction of the acidic functional group to the resins was observed.

ISSN:0148-6055    

DOI:10.1122/1.550485

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

The unsteady viscoelastic flow generated by the sudden application of a constant flow rate is experimentally examined for an abrupt contraction and a tapered one with a rectangular cross‐section. The velocity change with time is measured with a L.D.V. for a 1.0 wt % aqueous solution of polyacrylamide. The gentle overshoot in the centerline velocity, which may be due to the effect of extensional flow, is observed from the vicinity of the entrance of a small slit to the downstream far from the entrance. Furthermore it is found that the flow in the entrance region finally reaches the anomalous three dimensional flow with a dual peak form of the velocity profile.

ISSN:0148-6055    

DOI:10.1122/1.550487

出版商:The Society of Rheology    

年代:1994

数据来源: AIP

摘要:

The effect of fluid force on detergency has been experimentally investigated. More than one hundred wires of 50 μm in diameter, as a model of two dimensional soil, were set so as to adhere to a bottom flat plate of a two dimensional channel. The aqueous solution of surfactant and the dilute aqueous solution of polymer were made to flow through the channel and the pressure drop caused by the wires was measured. The drag and the drag coefficient (CD) of one wire were estimated with the pressure drop by the use of the law of momentum. The following results are obtained. For all solutions used, the drag increases and the drag coefficient decreases with an increase in the Reynolds number based on the wire diameter taken as the characteristic reference length. The solution of LAS, one of familiar anionic surfactants, givesCDvalues lower than the pure water, and the difference becomes marked as the concentration of the solution increases. A nonionic surfactant solution, AE 1.0%, shows a time dependent character; it provides about half of the correspondingCDvalue of water within a day since the solution was produced, while it gives nearly the same as that of water after 4 days have passed. TheCDfor dilute solution of polymer (PEO 20 ppm) in water is higher than those for water and surfactant solutions. Viscosities of the solutions tested were Newtonian and the magnitudes are in the same order for all three solutions. These results suggest that the variation ofCDobserved for the three solutions is not directly related to the solution viscosity but probably to other properties such as elastic force.

ISSN:0148-6055    

DOI:10.1122/1.550488

出版商:The Society of Rheology    

年代:1994

数据来源: AIP