ISSN:0021-8979    

DOI:10.1063/1.1658451

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Similar to the dislocations in polymers caused by chain displacement, disclinations are caused by chain kinking and twisting. Two simple kinds are considered, a twist disclination loop (due to chain twisting) and a wedge disclination loop (due to chain kinking). Their elastic properties are given including displacements, strain and stress fields, and strain energies. Some of their features are compared with those of dislocation loops. The role of disclination loops in the mechanical behavior of polymers is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658452

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Solid‐state light scattering using a red laser source has been applied to the study of spherulitic shells of polyethylene and gelatin. TheHvscattering patterns from a collection of shells are qualitatively similar to that of a spherulite. However a single shell gives a scattering pattern wherein several orders of maxima within the recordable range are visible. The relative intensity of the higher‐order maxima depends on the thickness of the shell. Theoretical scattering patterns have been calculated and are in general agreement with the experimental observation.

ISSN:0021-8979    

DOI:10.1063/1.1658453

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The mean lives of positrons annihilating in nitric acid treated polypropylene were determined. A long‐lifetime component with a mean life of about 50 nsec appeared when the polypropylene was treated in hot nitric acid for more than three hours. This was obviously due to the annihilation ofortho‐positronium in the microcavities in the polypropylene etched by the action of nitric acid. It is suggested that nitric acid attacks the amorphous part of polypropylene first and leaves a skeleton of crystalline form filled with microcavities. The change of the mean life and the intensity of the long lifetime component with the change of the nitric acid treatment time is discussed. The value of theo‐Ps diffusion coefficient in polypropylene is estimated to beD>4.5×10−4cm2sec−1and the potential of the barrier surrounding theo‐Ps in the cavity is estimated to be less than 1 eV.

ISSN:0021-8979    

DOI:10.1063/1.1658454

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In order to account for the morphology observed in surface replicas of polyethylene spherulites, two possible mathematical models are proposed. These are based on the requirement that lamellae with a given twist angle about the radius vector of the lamella form continuous surfaces. It was found possible to arrange the lamellae in such a way that the locus of all points of given lamellar twist within the spherulite was a continuous surface of three‐dimensional spiral form. A computer was used to plot out the ring structure to be expected on sections through the models, and these were compared with the actual ring structures observed on surface replicas of polyethylene spherulites. On all sections not passing through the spherulite center, both models show a double‐armed spiral form in keeping with observed structures. Sections passing through the centers of the models do not always give double‐armed spirals, depending on the model.

ISSN:0021-8979    

DOI:10.1063/1.1658455

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In solid polymers the mean lifetime &tgr;2ofortho‐positronium annihilating by pickoff depends upon the free volume. &tgr;2has been measured for five samples of relatively monodisperse atactic polystyrene over a temperature range from room temperature to 120°C. The number average molecular weight of the samples ranged from 50 100 to 640 000. For each sample the variation of &tgr;2with temperature indicated a glass transition about 13 deg below that measured on a differential scanning colorimeter. An increase in the glass transition temperature with molecular weight was observed. The &tgr;2lifetime, which depends upon the overlap of the positron component of theortho‐positronium atom with the lattice wavefunction, seems to be very sensitive to the cooperative motion about the chain axis which is associated with the glass transition.

ISSN:0021-8979    

DOI:10.1063/1.1658456

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The melting temperature of polyethylene crystals decreases and the lattice constants (bothaandb) and lattice distortion increase, but the macroscopic volume of the specimen does not change with electron irradiation. From these results a model of a deformed lattice structure with point defects produced by irradiation is proposed. Calculations indicate that the anisotropy of a polymer crystal (difference between the elastic modulus along the molecular axis and perpendicular to the axis) increases the range of the distortion in a crystal caused by a defect. The presence of lattice distortion in electron irradiated polymer single crystals produces observable features in the Moire´ patterns obtained from the crystals.

ISSN:0021-8979    

DOI:10.1063/1.1658457

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A commercial high‐density polyethylene has been crystallized in the Instron Capillary Rheometer under the combined influence of pressure and orientation. A transparent high‐modulus, and highly oriented filament structure was produced. In order to determine quantitatively the degree of orientation, azimuthal x‐ray scans of the 002 reflection plane were used to obtain the orientation function of the orthorhombic unit cell relative to the flow axis in the rheometer (identified with the filament axis). A value of +0.996±0.002 was measured for this orientation function indicating that the backbones of the crystalline polyethylene chains were virtually aligned perfectly parallel to the flow axis of the rheometer. This report is concerned with the high‐resolution techniques required to measure such highly oriented samples. In conjunction with the x‐ray study, birefringence measurements are included which permit the determination of the orientation of the amorphous component as well as the crystalline component.

ISSN:0021-8979    

DOI:10.1063/1.1658458

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Annealing treatments at elevated temperatures have been characterized by a specific infrared absorption assigned to the regularly folded chain segments in poly(ethylene terephthalate). The higher the annealing temperature, the more regular is the chain folding introduced into the fiber. When a fiber is free to contract, it will have a much larger amount of regular refolding than one which is held at constant length. Stretching is able to prevent refolding at low temperatures but in these experiments stretching was not able to prevent refolding at the highest temperatures. By comparing the above infrared results with small‐angle x‐ray diffraction and broadline nuclear magnetic resonance techniques, it is now possible to give validity to the interpretation that chain folds provide a structure which is a major contributor to the long period intensity and to the fluid‐like mobility at elevated temperatures. The external tension applied to a fiber during an annealing treatment will determine the internal shrinkage tension caused by the molecules during subsequent reheating. If chain refolding is allowed to occur during annealing, the potential for subsequent shrinkage and the amount of internal shrinkage tension are lowered, and higher temperatures are required to activate additional shrinkage. It thus appears that a major contributor to shrinkage and shrinkage tension in an oriented fiber is the refolding of molecules during thermal activation.

ISSN:0021-8979    

DOI:10.1063/1.1658459

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The morphological development of polyoxymethylene crystals polymerized from and grown within trioxane crystals was observed following irradiation of the trioxane with alpha particles and a subsequent heat treatment. A novel method of sample preparation enabled the morphology to be observed in detail and resulted in the discovery of new forms of polyoxymethylene crystals as well as an improved description of previously reported forms. A solid‐gas‐solid crystal growth mechanism was postulated to account for the predominantly acicular habit of the polyoxymethylene crystals.

ISSN:0021-8979    

DOI:10.1063/1.1658460

出版商:AIP    

年代:1970

数据来源: AIP