摘要:

AbstractThis paper brings together seven aspects of universality in viscoelasticity of linear flexible polymers: (1) the stress relaxation modulus G(t) being a universal function of the normalized molecular weight (MW), M/Me; (2) the MW dependence of the zero shear viscosity; (3) the MW dependence of the steady state compliance; (4) the MW dependence of the diffusion constant; (5) the damping functions; (6) slip‐stick melt fracture being a universal phenomenon; and (7) the number of entanglement strands per cubed entanglement distance being a universal constant. As presented in the text, the consistency, agreement and relation among these different aspects of universality can be properly brought to ligh

ISSN:0258-0322    

DOI:10.1002/masy.19920560103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractStarting from a slip‐link model, we derive a general strain measure for polymer melts. Predictions are compared to experimental data of uniaxial, planar, ellipsoidal, and equibiaxial extensions of a polyisobutylene (PIB) melt. The data do not support Doi's assumption that the tube diameter remains unchanged by deformation. The relative tube diameter and its inverse, the molecular stress function, can be extracted directly from the data. At small strains, the relative cross section of the tube is inversely proportional to the average stretch of the tub

ISSN:0258-0322    

DOI:10.1002/masy.19920560104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractRecent developments helped to solve some experimental problems in polymer melt rheometry: By a stability test one can find out whether under test conditions the individual polymer melt is sufficiently long stable. For melts with long relaxation times, an incomplete creep‐test followed by recovery is proposed to determine the linear viscoelastic material functions. In a cone‐and‐plate rheometer, a very constant heating system and the separation of the plate into a central disk and an outer ring allow us to measure the two normal stress differences in viscometric flows also at higher temperatures. For a commercial LCP, a special sample preparation technique is reported. Melt elongation followed by recovery in combination with morphological studies are presented for a polymer blend (PMMA/PS). From the combination of recovery after melt extension and morphology the interface tension between the melts of PS and PMMA can be deter

ISSN:0258-0322    

DOI:10.1002/masy.19920560105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0258-0322    

DOI:10.1002/masy.19920560106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractDisk‐like samples are submitted to controlled squeezing forces between parallel plates and the time‐dependent sample height is measured. Isothermal tests at constant force enable the determination of viscosity functions of melts. Experiments using a constant disk radius and a constant disk volume are compared. Creep and creep recovery tests are made possible by a height‐dependent control of the force. The evaluation of a pressure‐dependent yield stress is demonstrated for wax powder. The squeeze flow technique is of advantage for systems with a layer structure or matrices containing long fibres or mats. In non‐isothermal experiments on solidifying materials, either by crystallization or polymerization, the total deformation and the speed of solidification in processes like stamp moulding can be d

ISSN:0258-0322    

DOI:10.1002/masy.19920560107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis lecture attempts to elucidate rheological behavior of multiphase polymer systems through a comparison with our studies on much simpler systems such as suspensions of (a) non‐aggregating and (b) aggregating monodisperse spheres in viscoelastic media, (c) polymer latex in the same polymer liquids, and (d) emulsions or blends of two polymers with or without an emulsifying block copolymer. For the system (a) not only the viscosity η but also the modulus obey the known simple dependence on volume fraction ϕ of hard‐sphere suspensions, while for the system (b) the flow induced‐aggregation and dissociation of the particles govern the rheology. In the system (c), relaxations of entanglements of the adsorbed chains as well as the spatial distribution of the latexes are essential. For the emulsion (d) of a biased composition range (e.g., ϕ1>ϕ2) the matrix phase 1 dominates, unless η1<<η2. When η1≥ η2, deformation and/or bursting of the dispersed phase 2 take place. For those of an even composition, the viscosity is additive of those of the components and is enhanced by adding the emulsifying block copo

ISSN:0258-0322    

DOI:10.1002/masy.19920560108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractOne of the main features of lyotropic and thermotropic liquid‐crystalline (LC) polymers is non‐homogeneity of their structure, which is reflected in their rheological properties. Relationships between some kinds of heterogeneities, viz. dynamic textures, isotropic‐anisotropic biphasic region, superposition of different types of crystalline and mesophase structures, framework formed by fillers and rheological characteristics have been ana

ISSN:0258-0322    

DOI:10.1002/masy.19920560109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe molecular models of polymer physics (reptation, tube renewal) give a reasonable picture of the diffusion and relaxation of long and flexible chains: the concept of “tube renewal” (constraint release) added to the reptation idea explains the polydispersity effects for multimodal blends as well as for commercial linear polymers. The real issue now is to introduce these concepts in the formalism of non‐linear viscoelasticity in order to explain the experimental data, as a first step in the range of moderate rates of deformation, then at very high st

ISSN:0258-0322    

DOI:10.1002/masy.19920560110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTransient rheological behaviour of melts of flexible polymers can be described qualitatively by factorable constitutive equations, the functions of which can be obtained by oscillatory and step strain experiments. In start‐up experiments thermotropic LCP melts can exhibit very large overshoots of the stresses, followed by minima, after which steady states are reached through damped oscillations of the signals. It is also possible that the normal stress remains periodic for long times, with large amplitudes, as is shown for a nematic copolyester melt that has been squeezed during the gap setting process. These periodicities scale with the number of revolutions of the rotating plate. After cessation of flow the stresses relax quickly to values that may be unequal to zero and dependent on the position in the period of the stresses where flow is stopped. Dynamic experiments reveal that the melts are very elastic in that stat

ISSN:0258-0322    

DOI:10.1002/masy.19920560111

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe anisotropic form factor of polystyrene (PS) chains during tensile and simple shear flows in the melt has been measured by small angle neutron scattering (SANS) on quenched samples containing deuterium labeled chains. For all tensile experiments, carried out in a wide range of strain rates, including linear viscoelastic behaviour, the chain conformation is well predicted by a temporary network model involving the recoverable strain. For binary blends of two PS with different molecular weight, the technique allows to characterize the chain conformation of either species. The scattering patterns of sheared samples show that the principal directions of molecular orientation depend on the magnitude of the scattering vector q: At high q (local level on the chain) the orientation is close to 45° with respect to the shear axis, whereas at low q the chains appear to be almost aligned with the stream lines

ISSN:0258-0322    

DOI:10.1002/masy.19920560112

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY