摘要:

The essence of reverse roll coating is the rapid high‐shear flow in a small gap between two rigid cylinders rotating with opposed surface speeds. The flow field established in this gap, including the free surface locations and flow rate, is determined mainly by the balance of viscous and surface tension forces, as measured by the capillary number. Non‐Newtonian rheological behavior can strongly affect both the steady, uniform flow and the instabilities to which it is susceptible. Computed solutions of the governing equations indicate that flows of purely viscous liquids differ little from those of Newtonian liquids at the same capillary number, provided that the dimensionless force ratio is defined with the viscosity at the appropriate shear rate. Experiments with shear thinning but relatively inelastic algin solutions confirm this, with the exception that ribbing is strongly exaggerated, presumably by slight elasticity of the liquid. Experiments with highly elastic polyacrylamide solutions show that the coating thickness and the nature of the instabilities can be dramatically altered.

ISSN:0148-6055    

DOI:10.1122/1.550145

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

Shear stress and normal stress relaxation data were collected for a range of shear strains for a polystyrene–dibutyl phthalate solution. Data from single‐step shear strain experiments were used to test time–strain factorability and to check on the applicability of the Lodge–Meissner rule. Significant departures from time–strain factorability were found, but the shear and normal stress data were in excellent agreement with the Lodge–Meissner prediction. Data from double‐step shear strain experiments were used to check the predictions of the K–BKZ and Doi–Edwards theories. It was found that these theories do not generally provide adequate descriptions of double‐step shear strain deformations.

ISSN:0148-6055    

DOI:10.1122/1.550146

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

A viscosity anomaly in immiscible polymer blends takes place when the viscosity of its melt falls below the value calculated from the linear additivity rule applied to viscosities of the components. This work examines interfacial origins of the anomaly through a parallel analysis of morphology and flow rate of polypropylene–polystyrene blends. Experiments were conducted with a capillary rheometer using the method of layered blends. The method allows a convenient morphological characterization of collected extrudates. The combined knowledge of the morphology and flow rates enabled a quantitative analysis of flow patterns during the extrusion. Strong circumstantial evidence supports, but does not confirm, that interfacial effects contribute little, if any, to the observed viscosity anomaly.

ISSN:0148-6055    

DOI:10.1122/1.550147

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

Results are presented of a detailed rheological study of two different polyisobutylene systems in steady and transient shear flows. Shear‐thinning solutions are prepared by dissolving high molecular polyisobutylene in tetradecane, a low viscosity solvent. Nearly constant viscosity solutions are obtained by adding a third component of highly viscous polybutene. The linear viscoelastic behavior of these fluids is characterized in small‐amplitude oscillatory shearing flow and the nonlinear behavior is studied by means of steady and transient shear flows. The spectrum of relaxation times for both solutions has been determined. Temperature and concentration effects on the material functions are reported. Three differential constitutive equations with four relaxation modes were tested for fitting the experimental data in steady and transient shear flows: they are the quasilinear Oldroyd‐B model and the nonlinear Giesekus and Bird–DeAguiar models. The presence of nonlinear stress terms is found to be important for fitting the nonlinear material functions for both types of viscoelastic solutions.

ISSN:0148-6055    

DOI:10.1122/1.550148

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

The transient response of two thermotropic liquid crystalline polymers (a copolyester of 60 mol %p‐hydroxybenzoic acid, PHB, and 40 mol % poly(ethylene terephthalate), PET, and a copolyester of PHB and 2‐hydroxy‐6‐naphthoic acid, following step strains up to 20 strain units was measured. The relaxation curves typically show an initially rapid decay followed by a long relaxation tail. The lower the temperature, the more remarkable is the length of the long relaxation tail. This behavior makes the LCP uniquely different from most flexible chain polymers such as PET and polystyrene, which show a relaxation modulus which decreases continuously having no discontinuity in the slope. This behavior is probably due to unmelted solid phase which exists in the melt up to quite high temperatures. When the LCP’s are heated to temperatures well above their melting points as determined by DSC, then the long relaxation tails are eliminated. Furthermore, on cooling the sample rapidly down from a temperature well above the melting point the relaxation modulus resembles that at the higher temperature as a result of the supercooling effect. The relaxation modulus was also determined for samples subjected to lubricated squeezing flow. Whereas for polystyrene the relaxation modulus determined in lubricated squeezing flow was equal to that determined in step shear strain experiments, this was not the case for the LCP’s. It is not known whether the behavior reported here is common to nematic LCP’s or to the multiphase structure (crystallites, nematic phase, isotropic phase) which might be present.

ISSN:0148-6055    

DOI:10.1122/1.550149

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550152

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550101

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550102

出版商:The Society of Rheology    

年代:1990

数据来源: AIP