摘要:

A constitutive equation for liquid‐crystal polymer solutions is developed from phase space kinetic theory by modeling the polymer solution as a collection of rigid dumbbells suspended in a Newtonian solvent and subjected to anisotropic hydrodynamic drag. The isotropic to nematic phase transition is predicted by including polymer–polymer interaction through the Maier–Saupe mean‐field interaction potential. The diffusion equation for the configurational distribution function is the same as that used by Doi in his theory for concentrated solutions of rod‐like polymers. However, the expression obtained for the stress tensor contains an additional term involving the velocity gradient. The theory predicts the transitions to two nematic phases with prolate and oblate orientations, respectively, that evolve from the isotropic state as a transcritical bifurcation in the polymer concentration. The effects of a variety of deformations on the equilibrium phase behavior are presented. Multiple steady‐state nematic phases are predicted for both steady‐state shear and elongational flows; distinctly different states are identified for uniaxial and biaxial elongational flows. Material functions in shear and shearfree flows are determined, and the effect of anisotropic hydrodynamic drag on the rods is studied. Asymptotic behavior of the viscosity at high shear rates shows the importance of the additional term in the stress tensor expression.

ISSN:0148-6055    

DOI:10.1122/1.550452

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

We examine flow birefringence and flow modification effects (polymer‐induced changes in the flow field) for two‐dimensional extensional flows of polystyrene solutions at two concentrations in the semidilute regime. The concentrations of the polymer solutions are 1500 and 4500 ppm. This corresponds to ∼0.33 and 1.0×c*, the critical concentration for domain overlap of coiled polymer molecules at equilibrium. Results from a dilute 100 ppm solution of the same polymer sample are also presented for comparison. From the steady flow birefringence results, it appears that polymer chain extension is inhibited due to intermolecular interactions as the concentration is increased. In addition, inception of steady flow experiments show distinctive overshoots in birefringence. The main result of the velocity gradient measurements in this study is that the semidilute polymer solutions (1500 and 4500 ppm) show significant inhibition of high strain rates. The onset of flow modification corresponds to a critical effective volume concentration φ based upon spheres circumscribing the extended polymer chain of φc∼175 forbothsemidilute solutions. The degree of flow modification also shows correlation with φ using different concentration polymer solutions.

ISSN:0148-6055    

DOI:10.1122/1.550453

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

A molecular model, based on the concept of the activation rate theory, is developed for slip of a polymer as it flows through a die. The model correctly predicts the dependence of the critical shear stress for the onset of slip and the slip velocity of high molecular weight, linear polyethylene resins on temperature, pressure, wall shear stress, and molecular weight. It also predicts the increased slip which occurs when die surfaces are coated with a fluoropolymer having a low surface tension. It is not applicable at and above the critical shear stress for the onset of gross melt fracture.

ISSN:0148-6055    

DOI:10.1122/1.550456

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

The textures and the rheological behavior of a thermotropic copolyesteramide are characterized over five decades of shear rate. Three textures are observed, one thread‐like, one worm‐like characterized by a large density of defects and third, an ordered one characterized by a high flow orientation. The transitions from one texture to another depend on both shear rate and shear strain. Each texture corresponds to a given flow mechanism, similar to the ones found for lyotropics, and in qualitative agreement with the numerical predictions obtained from the rodlike solution model of Doi.

ISSN:0148-6055    

DOI:10.1122/1.550457

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

A common surfactant solution system is investigated to demonstrate the characteristic and generic features observed in shear‐thickening self‐assembling fluids. Rheological and flow birefringence measurements on the aqueous CTAB/sodium‐salicylate solutions disclose a number of unusual flow behaviors under different flow conditions. All solutions with concentrations ranging from 0.5 to 5 mM exhibit shear thickening above certain critical shear rates, accompanied by an increase in flow birefringence over a range of temperature fromT=14 to 36 °C. An extraordinarily long induction period, which is found to be inversely proportional to the applied shear rate, precedes the establishment of the shear‐thickening state. This dynamic state is highly flow birefringent, strongly nonlinear viscoelastic and possesses long relaxation times. We deduce that shear‐induced coagulation results in self‐assembling of surfactant molecules to form new micelles which are of exceedingly large sizes and which can survive against thermal disturbance for a long time.

ISSN:0148-6055    

DOI:10.1122/1.550458

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Post‐yield plateau of a true‐stress versus strain relation for glassy polymethyl methacrylate (PMMA) is illustrated to be a state of steady flow. A novel rate analysis applied to this steady flow provided a unique functional relation between the activation energy ΔHand the activation entropy ΔS. This functional relation for the PMMA glass is demonstrated to agree with a function of ΔHvs ΔSobtained from the relaxation data for the melt of the same PMMA sample. This agreement was also confirmed for polyvinyl chloride, polycarbonate, and polystyrene, thus giving direct evidence verifying a change of the metastable glassy structure into a liquid‐like structure in the polymer glasses. Hence, the yielding in the polymer glasses is convincingly concluded to be a transition phenomenon due to this structural change.

ISSN:0148-6055    

DOI:10.1122/1.550468

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Pigment dispersibility was studied for resins with various numbers of carboxyl groups at the chain end. The resins were synthesized by ring‐opening polymerization of ε‐carprolactone.G‐type resin had a carboxyl group at one end of each molecule.S‐type resin was a mixture of molecules with 0, 1, or 2 carboxyl groups at the end of molecules.P‐type resin was a tetrafunctional resin terminated with carboxyl groups.L‐type resin was without carboxyl groups. Dispersed pastes of Cu‐phthalocyanine blue usingG‐type resin revealed a higher degree of dispersion and a lower structural viscosity than pastes usingS‐type resin. TiO2dispersed pastes were prepared using mixtures ofG‐type resin andL‐type resin at various mixing ratios. As the amount ofG‐type resin increased, the degree of dispersion was enhanced and the yield value decreased.L‐type resin showed almost no effect on the yield values of TiO dispersed pastes. TiO2dispersed pastes usingP‐type resin showed a lower degree of dispersion and a higher structural viscosity than those usingG‐type resin. The resin molecules with no carboxyl groups did not affect the dispersibility or the structural viscosity of pigment dispersed pastes. The resin molecule with more than two carboxyl groups built up a structure among pigment particles and caused aggregation.

ISSN:0148-6055    

DOI:10.1122/1.550410

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Viscoelastic and forced Rayleigh scattering measurements were made on mixtures of PS and PVME over the wide range of temperature and PS molecular weight. The temperature dependence of the tracer diffusion coefficientDof PS in PVME was well described by the shift factoraTobtained from time‐temperature superposition of the dynamic shear modulus data of PVME in bulk. The dependence ofDon PS molecular weight was described by the free‐draining Rouse chain model in the lowMregion where the coil size of the diffusing PS chain is smaller than the mesh size of the PVME entanglement network. In the highMregion, on the other hand,Ddid not decrease in proportion toM−2, being in disagreement with the prediction of the reptation model, but took a constant value nearly equal to the calculatedDsvalue of the PVME molecule in bulk at the highMend. Two conjectures were proposed for interpretation of the above anomalous diffusion behavior.

ISSN:0148-6055    

DOI:10.1122/1.550411

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

In injection‐molded parts made of fiber reinforced thermoplastics, large warpages are frequently observed. The warpage is caused by anisotropic mechanical properties yielded by fiber orientations in molded parts. Therefore, it is necessary to predict fiber orientations and anisotropic mechanical properties for estimating the occurrence of warpages. A computer program for evaluating fiber orientation in molded parts was developed by using Folgar and Tucker’s planar orientation model that was considered as fiber–fiber interactions. The classical laminated plate theory was applied to predict mechanical properties (elastic modulus and thermal expansion coefficient) of molded parts in this study. The mechanical properties were predicted in the analysis from calculated fiber orientations and mechanical properties of the fiber and the polymer. Predicted elastic modulus and thermal expansion coefficient were compared with measured ones for a molded plate of glass‐fiber‐reinforced nylon‐6,6 (fiber content 30 wt. %) to verify computational method. Predicted results agreed with measured ones very well for both the elastic modulus and the thermal expansion coefficient.

ISSN:0148-6055    

DOI:10.1122/1.550412

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Effects of swimming and running trainings on mechanical properties of bone and bone density were investigated. Mechanical tests were conducted for tibial bone. The dynamic stiffness and tan δ were measured by a viscoelastic spectrometer. The three‐point bending test was performed with an Instron‐type universal testing machine. Bone mineral content was measured by photon absorptimetry at the middle site of the tibial bone. In the swimming case the stiffness and tan δ were, in average, larger for the trained rats than for the controlled group. The strength and the bone density were also larger for the trained group. In the running case, the negative effects were observed on these variables.

ISSN:0148-6055    

DOI:10.1122/1.550413

出版商:The Society of Rheology    

年代:1993

数据来源: AIP