摘要:

The altered free volume state (AFVS) approach developed by Kulkarni and Mashelkar has been extended to develop a model for viscosity of polymer latices. The effect of variables such as latex concentration, particle size, electrolyte concentration, and shear rate on latex viscosity can be satisfactorily explained within the framework of the AFVS model. The contribution of geometric and electrostatic factors to latex viscosity can be estimated in terms of the model parametersBηand β. Merits of the AFVS approach over the models proposed in the past have been elucidated. A unique superposition is shown to result for the effect of shear rate on the immobilization parameter β for various electrolyte concentrations.

ISSN:0148-6055    

DOI:10.1122/1.549895

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

The internal viscosity (IV) polymer chain model, which features an interbead connector functioning as a Hookean spring and a dashpot in parallel, is examined for the case of dumbbells(N=2)in the limit of very high IV. When the IV parameter Φ becomes very large, the moments of the configurational diffusion equation become identical to those of the rigid rod, thus establishing equivalence of rheological predictions for these two models. Next, an approximate linearization (preaveraging) technique for computing bead deformational and rotational velocities—previously found to give useful results in the limitΦ→0—is examined also in the limitΦ→∞.Predictions for non‐Newtonian viscosity and first normal stress coefficient are made using both the exact and approximate methods. Major differences are found, with the approximate method leading to an unrealistic (Newtonian) viscosity and vanishing normal stress, thus casting doubt on earlier results obtained with this method for high‐Nchains with large Φ. For the exact method, replacement of monodisperse dumbbells by a Gaussian distribution of dumbbell lengths has no effect on the low‐shear viscosity, but increases the low‐shear normal stress by a factor of 5/3; at high shear the two types of distributions give very similar results.

ISSN:0148-6055    

DOI:10.1122/1.549899

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

An analysis is presented of spherical and cylindrical sink flows of viscoelastic fluids. Stress levels and the rate of stress growth are found to be restricted to modest magnitudes in arbitrarily rapid cylindrical sink flows (flows through a wedge), but in contrast, stresses rise very rapidly to high levels during flows through conical channels. The analysis appears to be in qualitative agreement with the experimental results observed by James and Saringer for very dilute polymer solutions and is presented as an interpretation of those exceptional data. Consequences of the major differences between the two flow fields are explored briefly, and the range of applicability of the analysis is considered.

ISSN:0148-6055    

DOI:10.1122/1.549896

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

Measurements of dynamic viscoelastic properties in very small oscillating shear deformations have been made on solutions of a jet fuel, Jet A, containing an antimisting polymeric additive, FM‐9. A few measurements were also made on solutions of FM‐9 in a mixed solvent of mineral oil, tetralin, ando‐terphenyl. Two samples of FM‐9 had approximate number‐average molecular weights of 12,000,000 and 8,100,000 as deduced from analysis of the measurements. The ranges of variables were 2.42–4.03 g/L in concentration (0.3 to 0.5% by weight), 1–35°C, in temperature, 1.3–9.4 cp in solvent viscosity, and 103–6100 Hz in frequency. Measurements in the Jet A solvent were made both with and without a modifying carrier. The results were compared with the Zimm theory, and the viscoelastic behavior was found to resemble rather closely that of ordinary nonpolar polymers in Θ solvents. The relation of the results to the antithixotropic behavior of such solutions at high shear rates is discussed in terms of intramolecular and intermolecular interactions.

ISSN:0148-6055    

DOI:10.1122/1.549908

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

Thin film of isothermal Newtonian fluids lying on the(x,y)plane can be extended without generating thickness nonuniformity when the film is initially uniform in thickness and the velocity fieldvx(x,y,t),vy(x,y,t)of stretching obeys the equationsvx(x,y,t)=a(t)x+b(t)vx*(x,y),vy(x,y,t)=a(t)y+b(t)vy*(x,y),where(vx*,vy*)is identical to the two‐dimensional potential flow that satisfies the Cauchy‐Rieman equations in(x,y)coordinates, whilea(t)andb(t)are arbitrary time functions. Drawing on the knowledge of classical hydrodynamics a number of interesting and physically realizable flow fields of uniform thickness film stretching can be predicted analytically by the above solution(vy,vy),which also leads to the analytical proof that thickness uniformity is maintained in any axisymmetrical stretching as long as the film is uniform initially. These findings constitute an important correction to the authors' previous statement that thickness uniformity can be maintained only when the flow field consists of uniform extension inxandydirections expressible by the equationsvx=C11(t)x+C12(t)yandvy=C21(t)x+C22(t)y.

ISSN:0148-6055    

DOI:10.1122/1.549897

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

Solutions of poly(vinyl alcohol) (PVA) and polysaccharide with sodium borate (SB) are investigated as a model system for associating polymers which exhibit shear‐induced fluid structure and shear‐thickening rheology. Certain combinations of PVA and SB concentrations are shown to result in fluids that exhibit a viscosity maximum followed by shear thinning as shear rate is increased. Stress saturation is often observed in the shear‐thinning region. A significant hysteresis is also reported in which higher viscosities and lower shear rate for the viscosity maximum are observed in steady‐state measurements made while decreasing shear rate in a stepwise manner. Boron nuclear magnetic resonance spectra are shown to be useful for elucidating the nature of the borate/hydroxyl‐dyad complexes, including their stereoselectivity. Boron resonance peaks allow quantitative determination of the number of complexes. Dynamic mechanical properties are included, and a physical picture of network structure building and breaking during flow of associating polymers is discussed.

ISSN:0148-6055    

DOI:10.1122/1.549898

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

The rheological properties of a liquid crystalline copolymer have been studied as a function of time at constant temperature. The changes which occur with increasing time include (i) an increase in η*, (ii) an increase in the non‐Newtonian character of the flow, and (iii) an increase in the elasticity of the melt. The initial changes occur over a time scale of approximately 10 min; slower increases are found for times up to 120 min. A possible explanation for the effects observed is crystallization, i.e., the changes in rheological properties result from the presence of a continually increasing crystalline phase. Additional evidence which supports this hypothesis is presented. From a DSC study of the annealing of the polymer at high temperatures, the dependence of the crystal melting temperature on thermal history is demonstrated. The increase in melting temperature which is observed is consistent with the explanation proposed for the rheological changes. Finally, the results of a study of the time dependence of the rheological properties of a model isotropic copolyester, Kodar PETG, are presented. In many respects, the structural and crystallization characteristics of PETG are similar to those of the liquid crystalline polymer studied. Similar time dependence was found for the rheological properties of PETG.

ISSN:0148-6055    

DOI:10.1122/1.549901

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

A direct numerical method is presented which calculates the shear rates in concentric cylinder viscometers using an integration formula of interpolatory type. The shear rate is approximated using a piecewise cubic polynomial interpolating at four successive data points. The unequally spaced interpolation points are the shear stresses at either the inner or outer cylinder.

ISSN:0148-6055    

DOI:10.1122/1.549886

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

A mathematical model of the viscoelastic phenomenon employing derivatives of fractional order is examined in light of its consistency with thermodynamic principles. In particular, the development of constraints on parameters of the model ensure that the model predicts a nonnegative rate of energy dissipation and a nonnegative internal work. These constraints lead the model to predict realistic sinusoidal response as well as realistic relaxation and creep responses. Coupled with the established properties of the model, these attractive characteristics enhance its credibility for engineering analyses.

ISSN:0148-6055    

DOI:10.1122/1.549887

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

An approximate analysis is given for the inflation of a thin, flat circular disk of elastomeric material. The analysis results in a closed‐form analytical solution for the maximum displacement as a function of pressure. The method is illustrated through the use of a Mooney‐Rivlin material model. The results are compared with the exact solution, obtained by numerical means, and they are satisfactory, up into the range of several hundred percent strain. The method greatly simplifies the procedure for reducing test data, from this type of test, to nonlinear range mechanical properties.

ISSN:0148-6055    

DOI:10.1122/1.549847

出版商:The Society of Rheology    

年代:1986

数据来源: AIP