摘要:

AbstractDue to the symmetry which characterizes the surroundings of each chain segment in the amorphous melt all (but end) segments are equivalent in their embedment in space. Energetic interactions between segments are confined to segments in contact. Hence, in the presence of a surface only the segments actually in the surface layer will be affected and will have a statistical weight and Boltzmann factor different from segments in the bulk. The number of segments so involved is fixed, since the extent of the surface is controlled. The partition function is comprised of factors which depend neither upon the order of the segments in the chain nor upon the conformation of any particular chain. Only segments finding themselves in the surface contribute to the surface tension, with the largest contribution deriving from the density transition in the interface. This, at most temperatures, is confined to a lamella one segment layer, or less, thick. For polymer of high enough molecular weight end‐effects can be neglected and no allowance for the presence of ends is made here. It is then possible to reach a representation of surface tension in reduced coordinates, as shown already by Posner and Sanchez. Changes in chain conformation near the surface are calculate

ISSN:0258-0322    

DOI:10.1002/masy.19890230103

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractAlloying of polymers, now a standard technique for improving characteristics, is applied both to engineering and many mass plastics. Blending can be used to improve not only toughness, but optical properties or electrical conductivity. Mechanisms underlying the improved toughness of polymer alloys are discussed and the results of investigations reported. Future trends and implications for industry are considered.

ISSN:0258-0322    

DOI:10.1002/masy.19890230104

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractHitherto, compatibility in polyamide blends has been characterized by physical and mechanical methods exclusively. The work presented here describes the basis and potential of a chemical method for compatibility testing, transferred from protein chemistry (crosslinking technique). This method can also be applied, with appropriate modification, to synthetic polyamides. The degree of heterogeneity follows from the number of different molecule combinations.

ISSN:0258-0322    

DOI:10.1002/masy.19890230105

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractDiscrimination of elastically and inelastically scattered electrons in transmission electron microscopy (TEM) yields electron micrographs with enhanced and specific contrast. Highly resolved micrographs can be obtained in which the contrast reflects the local concentrations of specific elements. In the present work, Electron Spectroscopic Imaging (ESI) by means of a Zeiss EM 902 TEM is reported for polystyrene‐block‐poly(2‐vinylpyridine) diblock copolymers and for a series of differently crystallized polyethylene samples. Excellent contrast can be achieved without staining. The different techniques allow easy verification of the observed morph

ISSN:0258-0322    

DOI:10.1002/masy.19890230106

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractImportant flow enhancement effects take place when the motion of a non‐Newtonian fluid is driven either by pressure gradients pulsating around a non‐zero mean or by longitudinal and transversal boundary waves superposed on Poiseuille flow. Flow enhancement in the latter case is an order of magnitude larger than in the former. A regular perturbation in terms of the amplitude of the oscillation is used and closed form formulas given for mass transport rates at the lowest significant order. In particular it is shown that a mean flow may be generated even when the pressure gradients oscillate around a zero mean or the boundary waves are superposed on a fluid at rest if the frequencies of two superposed waves are in certain rat

ISSN:0258-0322    

DOI:10.1002/masy.19890230107

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe shape of the free surface and the flow field of a simple fluid driven by the steadily rotating bottom cap of a cylindrical cup is investigated. A regular domain perturbation in terms of the angular velocity of the bottom cap is used. The velocity field is a superposition of a strong primary, azimuthal field and a weaker secondary meridional field. The effect of the aspect ratio and viscoelasticity of the fluid results in multiple cell structures in the meridional plane. The free surface shape determined at the lowest significant order in the perturbation algorithm, is similarly affected by the same factors. Both the flow field and the interface shape are determined for a wide range of aspect ratios and viscoelastic parameters.

ISSN:0258-0322    

DOI:10.1002/masy.19890230108

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this study, six samples of commercial poly(vinylidene fluoride) are investigated. Dynamic and steady‐state shear flow experiments are carried out in the melt state in order to relate their rheological behaviour to their molecular weight distributions. This rheological investigation is performed through the use of some simple parameters related to the viscosity, elasticity and relaxation times. Plots of flow curves in reduced coordinates are used to confirm the above result

ISSN:0258-0322    

DOI:10.1002/masy.19890230109

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractUltrasonics is presented as a powerful method for the thermomechanical analysis of polymers. An experiment is described where the specific volume of a polymer is measured in simultaneity with the acoustic parameters. The technique allows full control of the thermal history in the temperature range from — 150°C to 300°C, where the material goes from a glasslike to a liquidlike state. Moreover the technique allows measurements to be performed at different pressures, up to 2 kbar. Results obtained on a typical amorphous polymer (polystyrene) are reported and the propagation of sound is discussed in regards to the well defined thermodynamic state for the material. Also, the results discriminate between the thermodynamic and the relaxational aspects of the glass transit

ISSN:0258-0322    

DOI:10.1002/masy.19890230110

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractProperties of interface in unidirectional composite materials can be studied “in situ” by dynamic mechanical measurements: analysis of relaxations and appearance of damage in shearing. This methodology is applied on composite materials based on an epoxy matrix and carbon fibers with different surface treatments (untreated, oxidized and sized). Mechanical spectroscopy displays modifications of epoxy network with the fiber treatment and evidence for an interphase in the case of sized fibers. Dynamic shearing test clearly shows large differences of behavior with the surface treatme

ISSN:0258-0322    

DOI:10.1002/masy.19890230111

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe transient rheological behaviour of a lyotropic polymeric liquid crystal is investigated. The system consists of a 12% by weight solution of poly(γ‐benzyl‐L‐glutamate) in m‐cresol. The structural changes caused by steady state shearing and by large amplitude oscillatory flow are measured. This is done by following the linear moduli upon cessation of flow. The stress transients during a stepwise increase in shear rate are used for the same purpose. Flow always increases the subsequent moduli in the system used, but the mode and the intensity of the flow have a complex effect. The variable domain structure seems to be responsible for most of the measured behaviour. The data put specific constraints on the detailed mechanisms that can contribute to the global transien

ISSN:0258-0322    

DOI:10.1002/masy.19890230112

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY