摘要:

Generalized creep and relaxation functions, appearing as kernels in the Fréchet‐Green‐Rivlin multiple integral developments of the response functionals, are related by a system of linear Volterra equations of the first order. The general form of these relations is given explicitly in the one‐dimensional case. The kernels of the Volterra equations obtained are the same for every order. They have hence the same resolvent kernel, derived simply from the relaxation function of order one. Furthermore, the relaxation function of order one depends only on the creep function of order one, through an equation identical to that obtained in linear viscoelasticity. The resolution of this last equation (by standard methods used in linear viscoelasticity) gives the solution for higher orders by quadratures. In the case without aging, the usual Carson‐Laplace transform method can be used to solve the first equation and perform the quadratures. These results have been obtained by direct calculations which are a little tedious and are not given here. However, an explicit derivation of the system of Volterra equations is given in the Appendix, for the nonaging case. This derivation is made by use of theHntransform, which is based on the multidimensional Carson‐Laplace transform.

ISSN:0148-6055    

DOI:10.1122/1.549789

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

A study of the viscosity rise during free radical crosslinking polymerization is presented. Techniques were developed for monitoring isothermal viscosity rise during fast polymerization reactions. The chemical system used was composed of a dimethacrylate resin in styrene monomer,t‐butyl perbenzoate initiator, and hydroquinone as the inhibitor. When reduced viscosity is plotted versus conversion, data at all temperatures collapsed into a single curve. A theoretical equation is suggested for the time required to reach the gel point in free radical crosslinking polymerization with inhibition. This equation showed good agreement with experimental observations.

ISSN:0148-6055    

DOI:10.1122/1.549790

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

Stress relaxation in shear has been measured at 25°C for a polyisobutylene sample with viscosity average molecular weight7.7×105,at shear strains γ from 0.2 to 0.5, over a time scale from102to104.5 s.In this range, the relaxation modulusG(γ;t)could be expressed by the productG(0;t)h(γ);atγ=0.5,h=0.76.Simultaneous measurements of the differential storage and loss shear moduli,G′(ω,γ;t)andG″(ω,γ;t)were made throughout the relaxation process by intermittently superposing small oscillating deformations with a maximum additional strain of 0.01, at a frequency of about 0.33 Hz, which falls in the middle of the plateau zone of the polymer. Forγ=0.2,G′andG″remained unchanged from their values at zero static strain,G′(ω,0)andG″(ω,0)respectively, confirming that the density of entanglements (or topological obstacles, or temporary network junctions), remains constant throughout the relaxation process at small strains. At higher strains,G″was nearly constant, butG′was somewhat smaller at the first measurement after imposition of static strain and slowly recovered to its original zero‐strain value. The behavior could be qualitatively interpreted by the Doi theory which includes both an equilibration process characterized by a timeτeand a disengagement process characterized by a timeτd;the decrease inG′would correspond to loss of entanglements by the contraction of stretched molecules during equilibration and the subsequent increase to reestablishment of new entanglements by reptation during disengagement.

ISSN:0148-6055    

DOI:10.1122/1.549791

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

In steady shear flow, sustained negative primary normal‐stress differences have been reported for several liquid crystalline systems, in most detail form‐cresol solutions of helicoidal polypeptides and for copolyesters. A theoretical model is herewith proposed in which “dumbbell” molecules are constrained from rotating freely in the shear flow by the intermolecular potential that produces liquid crystalline order. In steady state, the molecules are imperfectly aligned, corresponding to a shortening or buckling of molecular layers. The tendency for the layers to straighten toward perfect order causes a compressive force along the streamlines, corresponding to a negative normal stress. For this actually to occur, a dimensionless group (containing the molecular axial ratio, shear rate, solute volume fraction and intermolecular potential) is predicted to be within a restricted range. The experimentally observed range for the polypeptide solutions is wider, probably because of polydispersity (imperfect monodispersity), and the theory underestimates the magnitude of observed negative normal stress. Although the copolyesters must be characterized by different independent variables, again one can identify a dimensionless group such that all the negative normal stresses occur within a restricted range. This simple model identifies dimensionless variables that will be important in any detailed microrheological theory based on calculating the distribution of molecular orientations.

ISSN:0148-6055    

DOI:10.1122/1.549792

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

The volume flow of poly(butylene terephthalate) (PBT) ofM̄n=19,600,Tm=598 KandTg=316 K,has been measured in an Instron Capillary Rheometer. The elastic modulus of the longitudinal wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at temperatures above the melting temperature (493 K), and compression rates of ca. 1 to200×10−5 s−1.An increase in longitudinal volume viscosity with decreasing volume deformation, increasing compression rate, and increasing temperature has been observed. The volume flow activation energy decreases as the volume deformation increases.

ISSN:0148-6055    

DOI:10.1122/1.549810

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

Five samples of linear low density polyethylene, polymerized withl‐butene as comonomer and having different molecular weights but similar molecular weight distributions, have been characterized in shear and nonisothermal elongational flow. From the experimental data, generalized relationships have been found for the zero shear viscosity, the shift factors of the whole viscosity curve, the critical shear rate, the melt strength and the breaking‐stretching ratio. It is then possible to predict with very good confidence values for the most important rheological characteristics of any LLDPE of similar polydispersity from the sole knowledge of the weight average molecular weight, in the range of temperature and flow conditions of industrial interest.

ISSN:0148-6055    

DOI:10.1122/1.549793

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

In the vane method for measuring the yield stress, the conventional analysis assumes that the stress is uniformly distributed on a cylindrical sheared surface to calculate the yield stress from the maximum torque and vane dimensions. By using two simple procedures, the present work shows that this assumption is justified at the moment of yielding. The yield stress calculated using the proposed methods compares favorably with that obtained with the conventional procedure. A comparison with the yield stress independently determined by other methods again confirms the usefulness of the vane technique as a simple but accurate method for direct yield stress measurement.

ISSN:0148-6055    

DOI:10.1122/1.549794

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

摘要:

The rheological and pipeline flow behavior of corn starch dispersions has been studied. It was found that the flow characteristics of these systems gave dilatant (shear thickening) behavior until a critical shear rate was attained at which point Newtonian behavior commenced. This critical shear rate, as well as the behavior of power law index and consistency index were found to be functions of percent volume concentration. Additionally, the behavior of these rheological parameters was explained on the basis of an existing theory describing shear thickening. Pipeline flow data confirmed that dilatant (shear thickening) fluids followed the Metzner‐Reed friction factor relationships in the laminar region. The range of behavior was extended to fluids havingnvalues of 2.92 and volume concentrations of 40.0 percent. Finally, it was found that transition and turbulent flow could not be attained for dilatant (shear thickening) corn starch suspensions. This principally occurred because the critical shear rates yielding Newtonian behavior were excluded.

ISSN:0148-6055    

DOI:10.1122/1.549816

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549817

出版商:The Society of Rheology    

年代:1985

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549795

出版商:The Society of Rheology    

年代:1985

数据来源: AIP