摘要:

A study, based upon the Gibbs free energy, is made of the thermodynamical behaviour of dissipative and memory‐dependent materials. The creep‐function mechanical properties involved are generalizations of the usual volumetric compressibility, the coefficient of thermal expansion, and the specific heat at constant pressure. It is found that under a certain special equilibrium condition, a transition behaviour occurs in the material whereby the mechanical and thermal properties change with time. The criterion for its occurrence is that of a certain proportionality between the volumetric, thermal expansion and specific‐heat creep functions. This criterion is interpreted as that of the glass‐transition temperature, the resulting forms bear some resemblance to those of an Ehrenfest second‐order transition. However, the similarity is only superficial since herein full account is taken of time‐dependent memory effects. Attention is given to the relationship of the present work to previous studies, which did not specifically account for time‐dependent memory effects, but which did account for some type of irreversible process through the use of “internal variables.” The application of the present criterion suggests a specific and new means of unambiguously determining the glass‐transition temperature for polymers. Also, the thermodynamic study indicates some avenues of research into the underlying kinetic causes of glass‐transition behaviour.

ISSN:0148-6055    

DOI:10.1122/1.549460

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

The viscosities of concentrated suspensions of glass fibers in high viscosity silicone oils were measured with a14″capillary viscometer. Suspensions were mixed by various techniques, but only data for extruder mixed suspensions are presented. All pertinent suspension parameters were monitored, including wall effects. Yield stresses, squeeze‐through, and capillary entrance exclusion were observed. Both the quantitative and qualitative aspects of fiber suspension rheology depended strongly on fiber length, which is consistent with the variety of behavior reported in the literature. Controlling fiber length independent of changes in other suspension parameters is difficult.

ISSN:0148-6055    

DOI:10.1122/1.549453

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

Capillary viscometer data are reported for 0, 15, and 30 vol. % glass fiber suspensions in 100, 600, and 1000 P silicone oils. All other suspension parameters, including fiber length distribution, were constant. Wall effects were not significant. The viscosity data at each concentration were fit by a dimensionless plot of the formF(fNRe,NEl)=0whenfis the friction factor for tube flow andNReandNElare the Reynolds and Ellis numbers of the system. Suspension viscosity increased with fiber concentration, but the magnitude of the increase was highly shear rate dependent. The dependence of viscosity on fiber concentration and shear rate is compared with literature predictions.

ISSN:0148-6055    

DOI:10.1122/1.549454

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

The orthogonal rheometer has become increasingly popular for determination of the viscoelastic properties of fluids. Here we present an analytical solution for the steady‐state temperature distribution arising from the dissipation due to flow between infinite, isothermal eccentric rotating disks. This information is necessary to experimentalists concerned with obtaining accurate rheological characterizations for materials whose properties are temperature dependent, e.g., polymer melts. The results, temperature profiles and the maximum temperature rise, are presented using two dimensionless parameters which indicate the effects of inertia and fluid elasticity. Thus, the results can be easily used by practitioners to estimate the importance of dissipation in their experiments. For conditions of practical interest, temperature rises large enough to be of concern may be encountered.

ISSN:0148-6055    

DOI:10.1122/1.549455

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

A number of series of water‐in‐oil creams were prepared in which the oil phase consisted of liquid paraffin and microcrystalline wax. The emulsifying agent employed was polyoxyethylenel oleyl ether. The dynamic viscoelastic properties of the creams, and also of the oil phases, were measured at 25°C with a Weissenberg rheogoniometer at frequencies ranging from5×10−3to 1.582 Hz. The frequency dependence of viscoelastic functions was influenced much by the change in the weight fractions of water, but little by the change in the ratios of microcrystalline wax to liquid paraffin. The gradient of curves in logarithmic plots of the viscoelastic functions of the creams against the weight fraction of water changed drastically at a certain weight fraction of water. These results of viscoelastic measurements were compatible with the microscopic appearance of the creams that large particles of microcrystalline wax were dispersed through the liquid paraffin medium, together with emulsified water drops of much smaller size. The observed dependence of the viscoelastic functions on the weight fraction of water was explained qualitatively by the theory of viscoelastic properties of disperse system proposed by Okano.

ISSN:0148-6055    

DOI:10.1122/1.549439

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

Rheogoniometric and fiber spinning experiments were carried out using polyacrylamide solutions containing 100, 200, and 300 ppm of polymer. The stress levels in the extensional flow experiments were 1–3 orders of magnitude greater than those which would have been exhibited by Newtonian fluids of identical viscosity level. Since the stresses arising in extensional flows of simple fluids are very sensitive to the distant deformation history of the material,whereas the recent history is of dominant importance in shearing flows, the ability to model both deformation processes with a common constitutive equation is a very severe test of the latter, and one which is of importance in a variety of processing areas. An evaluation of several constitutive relations is presented; two derivative models are found to portray the results with reasonable accuracy, although a given set of material parameters does not suffice for predicting all of the stresses measured in both shearing and extension.

ISSN:0148-6055    

DOI:10.1122/1.549440

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

For a commercial polyisobutylene, at room temperature, stress relaxation after a sudden imposition of a shear or elongational strain has been performed in the limit of linear viscoelasticity. Transient shear and elongational stresses have been determined in the non‐linear region by using a Universal Instron Testing Machine. While for shear flow steady‐state conditions were reached in some cases, the elongational results are only transient because the experimental procedure gives a rate of stretching which decreases in time. Some steady shear results have been obtained at higher temperatures with a capillary viscometer. The results have been interpreted by means of a one‐parameter model which attributes the non‐linearities arising from the change in the spectrum of relaxation times to modification of the entangled network. The Bogue‐White model has been also considered for comparison.

ISSN:0148-6055    

DOI:10.1122/1.549466

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

A series of polydimethylsiloxane based multiblock[AB]ncopolymers was prepared and characterized. The hard blocks included poly(aryl ethers), poly(aryl esters), poly(aryl carbonates), a poly(cycloaliphatic carbonate), polystyrene, and poly(α‐methylsytrene). All of these materials could be solution cast into films which had attractive physical properties and which displayed two‐phase behavior. However, their rheological characteristics (in particular their melt processibility) were found to differ dramatically when the chemical structure of the hard block was varied. Thus, the polysulfone‐polydimethylsiloxane block copolymer could not even be satisfactorily compression molded owing to its inordinately high melt viscosity and melt elasticity. On the other hand, the copolymer prepared from the polycarbonate of 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol could be readily molded and extruded. The behavior is believed to be related to the retention of a physical network at temperatures well above the upper glass transition. Available data are in agreement with this interpretation. It is proposed that processibility characteristics of block copolymers are related to the intersegment solubility parameter differential, Δ. Our preliminary results suggest that an optimum balance of engineering properties and processibility in two‐phase block or graft copolymers should be observed when the value of Δ is approximately unity. For crystallizable systems, the Δ value in the polymer melt should be essentially zero, if one or both of the segments can subsequently crystallize and hence induce microphase separation.

ISSN:0148-6055    

DOI:10.1122/1.549467

出版商:The Society of Rheology    

年代:1977

数据来源: AIP

摘要:

A linearized stability theory for the flow of a hot fluid in a cold channel is adapted here to the case of a moving boundary characteristic of injection molding of thermoplastics. The predictions for instability fall within expected experimental limits and two photographs show experimental evidence of a phenomenon that may arise in the manner predicted by the analysis.

ISSN:0148-6055    

DOI:10.1122/1.549441

出版商:The Society of Rheology    

年代:1977

数据来源: AIP