Volume 24, Issue 2, April 1980
Index of content:
Experimental Tests of a Few Constitutive Models for Polymer Solutions Based on Birefringence Data in Time‐Dependent Fields24(1980); http://dx.doi.org/10.1122/1.549560View Description Hide Description
Experimental tests of a few constitutive models were performed on the basis of time‐dependent stress data for an 8% polystyrene solution in chlorinated biphenyl. The strain‐dependent relaxation modulus G was measured with a cone‐and‐plate relaxometer. The shear stress σ and the first normal stress difference at the start and on the cessation of shear flow were evaluated from previous results of flowbirefringencemeasurement. The BKZ model consistently described the relation between σ and on the cessation of shear flow. A BKZ relation, corresponding to the van Es‐Christensen relation for the rate‐dependent constitutive model, held good for the stresses at the start of shear flow. The BKZ model calculation starting from G gave σ and slightly different from those observed at high rates of shear. The deviation may be removed by allowing a slight rate dependence of the memory function as was done by Macdonald. The model of Acierno‐La Mantia‐Marrucci‐Titomanlio gave a too marked overshoot of The model predicted a too large truncation at long times of the relaxation modulus with increasing magnitude of shear.
24(1980); http://dx.doi.org/10.1122/1.549559View Description Hide Description
A dilute solution of flexible macromolecules is modeled as a dilute suspension of dumbbells with slightly nonlinear elasticconnectors (nearly‐Hookean dumbbells) and subject to Browian motion. The molecular variables are eliminated directly from the kinetic theory by means of a perturbation scheme to give an expression for the stress tensor which is good for flows that do not deform the dumbbells drastically. The stress tensor is expressed in terms of several structure tensors, each of which is given by an auxiliary differential equation. This Hand form of the rheological equation of state can also be expressed in an Oldroyd form or as a memory integral expansion. Calculations of rheological properties for the model show substantial improvements over Hookean dumbbell predictions. In an appendix the distribution function for the nearly‐Hookean dumbbell is derived, and it can be used to obtain the same rheological equation of state by traditional methods.
24(1980); http://dx.doi.org/10.1122/1.549561View Description Hide Description
Axial velocity measurements in the die entry region of a capillary rheometer using a laser Doppler anemometer and a data logging system are reported for a Newtonian silicone oil and a highly elasticpolymer solution under low Reynolds number flow conditions For the silicone oil, major velocity rearrangements occur within one diameter distance upstream and the velocity distribution is independent of Reynolds number and die ratio within the range investigated. For the polymer solution, the stable converging flow field is characterized by a constant Deborah number, The axial velocity distribution becomes unsymmetric at followed by the development of spiralling instabilities at higher values of The site of initiation of the instabilities is at the die entry plane or downstream in the die land region.
24(1980); http://dx.doi.org/10.1122/1.549591View Description Hide Description
When subjected to creep test, aluminum exhibits characteristics which are analogous to those of thermorheologically simple material in the sense that on a plot of logarithm of creep function versus logarithm of time the curves corresponding to different stresses have the same shape so that they all could be shifted to form a master curve. Based on this observation and in analogy with the idea of time‐temperature superposition, a theory for viscoelastic materials is developed in which the natural time appearing explicity in the argument of relaxation or creep function is replaced by a suitable scalar‐valued function of stress tensor.
24(1980); http://dx.doi.org/10.1122/1.549562View Description Hide Description
Measurements were taken of the bulk rheological properties of concentrated emulsions, using a Weissenberg rheogoniometer. The emulsions investigated were various composition ratios of the following systems: (a) a viscoelastic‐viscoelasticsystem consisting of a 2 wt % aqueous solution of polyacrylamide (Separan AP 30) and a 6 wt % solution of polyisobutylene (PIB) in decalin; (b) a Newtonian‐viscoelastic system consisting of low‐molecular‐weight polybutene (Indopol L50) and a 2 wt % aqueous solution of polyacrylamide; (c) a Newtonian‐Newtonian system consisting of low‐molecular‐weight polybutene (Indopol L100) and glycerine. Emulsions were prepared first by using a stirrer and then by circulating the premixed emulsion through a gear pump in a closed‐loop flow system, until equilibrium droplet sizes were obtained. It was found that the bulk viscosity and elasticity (i.e., first normal stress difference) of an emulsionsystem go through a minimum and/or through a maximum at certain composition ratios, and that the state of dispersion of one liquid in another has a profound influence on the observed bulk rheological behavior. The seemingly peculiar bulk rheological behavior observed is explained with the aid of photomicrographs describing the state of dispersion of one liquid in another. It is of interest to mention that certain emulsions of glycerine and Indopol exhibit non‐Newtonian viscoelastic behavior although the individual components are strictly Newtonian fluids. This rather unusual behavior is explained in the light of the existing phenomenological theories.
24(1980); http://dx.doi.org/10.1122/1.549563View Description Hide Description
Time‐dependent viscoelasticmeasurements on suspension were investigated. To characterize the structural state, an “instantaneous” viscoelastic function was used, which was obtained by Fourier transformation of the resultant stress to pulse strain of the cosine type. The experiments were made on a suspension of glass beads in a polystyrene solution using a coaxial cylinder rheometer. When the time‐scale of the measurement is comparable with that of the structural change, the measured stress for a sinusoidal strain contains the response due to the structural change besides the viscoelastic response. Therefore, a conventional dynamic method is not applicable to such time‐dependent materials. However, as the time‐scale of a pulse strain is quite different from that of the structural change, the method used provides useful information on the relaxation process during the structural change.
24(1980); http://dx.doi.org/10.1122/1.549592View Description Hide Description
24(1980); http://dx.doi.org/10.1122/1.549603View Description Hide Description