摘要:

The rheological transients in simple shear flow of a dilute, initially isotropic suspension of monodisperse spheroids having strong rotary Brownian motion are considered theoretically. The principal rheological properties of an initially isotropic suspension are calculated from the principal stresses and show changes due to the Brownian diffusion. The intrinsic normal stress differenceξ31in the direction of flow starts from zero, increasing initially until a steady state is reached asymptotically. Similar behavior is shown by the intrinsic viscosity η, except for the initial nonzero value. On the other hand, the intrinsic normal stress differenceξ21in the direction normal to the flow increases from zero to pass through a maximum and then decays until it reaches an asymptotic negative value. The significance of these predictions is discussed briefly.

ISSN:0148-6055    

DOI:10.1122/1.549580

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

In earlier papers (Parts I and II) we gave the perturbation analysis for the prediction of the free surface on a simple fluid near an oscillating rod and presented the results of a preliminary experiment involving a single rod in one sample of simple fluid. In this paper we report the results of a recent more extensive experimental investigation aimed at testing the predictions of the theory. These experiments involve the use of two different simple fluids and three rods of differing diameters. The experimental results reinforce our earlier results and substantiate the predictions of the theory with respect to the diameter dependence of the normalized height of climb at the rod surface. The rapid increase in fluid temperature near the rod caused by shear heating is illustrated, and the asymptotic form of the theory for large angular frequencies is derived.

ISSN:0148-6055    

DOI:10.1122/1.549599

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

A method for predicting the velocity profile in a one‐dimensional, slow moving, laminar fluid in which yield stress varies with depth is presented in this paper. The governing equations are solved for two types of yield stress gradients [τ0=τaYbandτ0=a(Y−La)]. The depth of the flowing layer and velocity profile are given as algebraic equations in these cases. A yield stress gradient can exist whenever high concentrations of fine‐grained solids are settling and compacting (e.g., dredged material containment area, high‐rate settler).

ISSN:0148-6055    

DOI:10.1122/1.549581

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The viscosities and primary normal stress coefficients are presented for well characterized, rubber‐modified polystyrene as a function of shear rate, temperature, rubber phase volume fraction, and molecular weight. From these data, melt relaxation times and shear compliances are calculated and related to the polystyrene matrix molecular weight and rubber phase volume fraction. The matrix and rubber‐modified melt compliance data are compared to values predicted from molecular and continuum theories.

ISSN:0148-6055    

DOI:10.1122/1.549582

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The viscosity behavior of polymer solutions at high concentrations and elevated temperatures is of scientific and technological importance. Nonetheless, few data covering this regime are extant, due in part to the difficulty of making the appropriate measurements. A new capillary rheometry method using a pressurized exit chamber, described by the author in a previous paper, was used to obtain a systematic body of viscosity data for the system polystyrene–ethylbenzene at elevated temperatures (60–255°C) and high concentrations (40–100% polymer). The temperature dependence of viscosity was representable in terms of flow curve shear rate‐temperature superposition over the entire concentration range investigated, with the shift factor temperature dependence being quantitatively described by an Arrhenius‐type relation at temperatures well aboveTg,yielding energies of activation for viscous flow as a well‐defined function of concentration over the entire concentration range. The concentration dependence of the Newtonian limiting viscosities was evaluated over the 40–100% range at both isothermal and isofree volume conditions. This observed dependence was considerably more severe than that projected from results in the literature obtained at lower concentrations and closer toTg.

ISSN:0148-6055    

DOI:10.1122/1.549600

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The flow behavior at 25°C for decalin solutions of polystyrenes (PS) of molecular weights up to7×106and polyisobutenes (PIB) of molecular weights up to3×106was examined over a wide range of shear rate up to about105 sec−1for several polymer concentrations. Measurements involved conventional glass capillary viscometers, a Rheometrics Mechanical Spectrometer, and custom‐built high‐shear concentric cylinder viscometer. Low‐shear Newtonian viscosities for the higher concentration entanglement region follow the formsη0=CM0.57for PS andη0=CM0.68for PIB. Gel permeation chromatography was used to determine polymer molecular weight, its distribution, and possible change on shearing. Shear degradation was observed for polymers at high values of concentration, molecular weight, and shear stress.

ISSN:0148-6055    

DOI:10.1122/1.549583

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

Two novel phenomena were observed in steady and transient shear measurements which were made in a Couette device of a R‐17 Weissenberg Rheogoniometer with suspensions of polystyrene spheres, 40–50 μm in diameter, suspended in a mixture of silicone oils at volume fractions0⩽φ0.55.Whenφ⩾0.3,the steady‐shear viscosity at a given shear rate was found to drift for many hours to an asymptotic value which, in contrast to the scatter of the initial measurements, was very reproducible. Again, whenφ⩾0.3,the shear stress showed a memory for the direction of previous shearing when the shear was stopped for a while and then restarted with either the same or the opposite sign. Moreover, during oscillatory shear experiments, these suspensions exhibited a nonlinear response which in fact could be predicted from their response to a sudden reversal of the direction of steady shear. It would appear, therefore, that such concentrated two‐phase systems cannot be modeled as isotropic fluids having a scalar effective viscosity unless the solids concentration is low.

ISSN:0148-6055    

DOI:10.1122/1.549584

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

Polycarbonate of Bisphenol A specimens were deformed in tension until a necked region was formed. Specimens extracted from the necked region were tested in order to detect thermal expansion, as well as dynamic behavior of the deformed material. A comparison of the thermal and dynamic behavior between deformed and nondeformed material was made. The dynamic behavior was investigated over a wide temperature range using a direct‐reading dynamic viscoelastometer. Storage and loss moduli, as well as mechanical damping factors of the two kinds of specimens were measured as functions of temperature. It was found that dynamic experiments constitute sensitive methods for detecting secondary transition temperatures. This statement is not valid in the case of oriented polycarbonate where secondary transitions can be determined equally well by means of thermal and dynamic measurements. On the other hand, it was found that chain orientation in this material increases bothE′andE″,while relative ratioE1′/E2′remains almost independent of the frequency. Finally, the effect of the crystallization produced during extension on the position ofTgseems to be negligible.

ISSN:0148-6055    

DOI:10.1122/1.549585

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

In unsteady hydrodynamic lubrication the film thickness varies with time, producing the squeeze film term in the Reynolds equation, where the fluid is assumed to be Newtonian and fluid inertia effects are neglected. A Deborah and Reynolds number perturbation solution correction to lubrication theory is presented which can accommodate arbitrary smooth two‐dimensional surface geometry and arbitrary time variation in film thickness. The constitutive equation used is one recently proposed by Harnoy in which a new type of material derivative is used allowing separate consideration of relaxation and normal stress effects, each governed by a separate material parameter. A low Deborah number expansion is developed to obtain a simple two‐parameter (viscosity and relaxation time) stress‐explicit relation. Corrections to the lubrication theory for inertia and viscoelastic effects in terms of Reynolds and Deborah numbers are presented. Solutions to several problems are presented: (1) parallel surfaces with constant approach velocity, (2) parallel surfaces with constant load, and (3) the squeeze film damper bearing. Important phase shifting effects between the squeezing rate and the load are now exhibited, whereas lubrication theory requires that they be exactly in phase.

ISSN:0148-6055    

DOI:10.1122/1.549586

出版商:The Society of Rheology    

年代:1980

数据来源: AIP

摘要:

The elongational viscosity and the tensile compliance on four polystyrenes of different molecular weights and molecular‐weight distributions were determined by means of an extensional rheometer designed particularly for investigations on a small amount of polymer. The steady‐state elongational viscosity at small strain rates is three times the zero‐shear viscosity according to the Trouton relationship. The Trouton viscosity is proportional toMw3.5independent of the molecular weight distribution. For the steady‐state tensile compliance in the linear range of elongation no quantitative relationship with molecular data can be given but a strong increase of the compliance due to small amounts of a higher molecular weight component is observed. In the nonlinear range of elongation a small viscosity maximum as a function of tensile stress is observed for three samples whereas one sample shows an increase of the elongational viscosity up to values which are at least five times higher than the elongational viscosity in the linear range. The viscosity increase can be related to a pronounced high‐molecular‐weight tail in the molecular weight distribution. This result gives a hint to an explanation of the different and partly contradictory findings in the literature on the strain‐rate dependence of the elongational viscosity of various polymer melts.

ISSN:0148-6055    

DOI:10.1122/1.549587

出版商:The Society of Rheology    

年代:1980

数据来源: AIP