摘要:

The solubilities of helium, nitrogen, oxygen, argon, methane, carbon dioxide, and ethane in glassy amorphous and crystalline polyethylene terephthalate have been studied by time‐lag and/or static sorption methods. Solubilities of all the gases but ethane were also determined in the rubbery crystalline polymer. The only deviations from Henry's law were displayed by ethane at 25°C and carbon dioxide at 25° and 40° C in the glassy polymer. Correlation of solubility constants for oxygen and nitrogen obtained by the static sorption method with values obtained dynamically indicate that the glassy crystalline polymer is an isotropic diffusion medium. Sorption in the glassy amorphous and crystalline polymers generally takes place by two processes operating concurrently: ordinary dissolution plus ``hole‐filling.'' The ``hole‐filling'' process obeys a Langmuir expression and dissolution obeys Henry's law for sorption of carbon dioxide in the amorphous polymer at 25°C. Crystallinity reduces gas solubility in the glassy polymer, but not generally in direct proportion to the decrease in amorphous volume. An exception is helium, which appears to obey the simple law,k=k*&agr;. The glassy state of the partially crystalline polymer extends to about 80–85°C where a transition region is noted on a van't Hoff plot for solubility constants. The other extremity of this region (about 95°C) marks the onset of rubber‐like behavior in the polymer. Heats of sorption in the glassy crystalline polymer are more exothermic than in the rubbery crystalline polymer, characteristic of the transition from sorption by dissolution and void‐filling processes to dissolution alone. The heat of solution of helium is slightly positive in both the glassy and rubbery states of the crystalline polymer, with no evidence of a break atTg. It appears that the major contribution to helium sorption in either state of the crystalline polymer is ordinary dissolution. In both the glassy and rubbery states, carbon dioxide shows evidence of a polar interaction with the polymer. Solubility constants are correlated with gas force constants &egr;/k¯in both the glassy amorphous and rubbery crystalline polymers.

ISSN:0021-8979    

DOI:10.1063/1.1729066

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Diffusion of helium, oxygen, nitrogen, argon, carbon dioxide, and methane in glassy and rubbery polythylene terephthalate has been studied in the range 25° to 130°C. Despite the abnormal solution behavior of these gases in the glassy polymer, the diffusion process is evidently normal and Fickian: Correlation of solubility constants for oxygen and nitrogen, obtained by the time‐lag method, with data obtained by a static sorption method, indicates that glassy crystalline polyethylene terephthalate may be considered an isotropic diffusion medium. Diffusion is impeded purely geometrically by the presence of the crystallites, and the impedance factor is equal to the reciprocal of the amorphous volume fraction. In the rubbery crystalline state of the polymer, diffusion is Fickian and apparent activation energies for diffusion are larger than those in the glassy crystalline polymer. A model for diffusion in the glassy amorphous and crystalline polymers is proposed, assuming that the driving force for diffusion is the concentration gradient of dissolved molecules which are assumed to be in local equilibrium with molecules in the ``holes.'' The model predicts that actual diffusion constants and activation energies are larger than those experimentally measured. Thus, part of the observed difference between values ofEDain the glassy and rubbery states may be reconciled. Correlations ofDandEDawith the square of gas molecular diameters are obtained in both the glassy and rubbery states. In the latter plots, the helium data fall above the correlations, showing evidence of partially non‐activated diffusion in both states of the polymer.

ISSN:0021-8979    

DOI:10.1063/1.1729054

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An idealized free‐vibration experiment is analyzed on the basis of the theory of infinitesimal linear viscoelasticity. The resulting motion can be expressed as a sum of terms, of which some are damped sinusoidal waves while others are negative exponentials in time. For some three parameter models of viscoelastic behavior, the results of this theory are compared with those of the usual treatment which leads to a simple damped sinusoidal wave.

ISSN:0021-8979    

DOI:10.1063/1.1729071

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The mathematical treatment of light scattering by regular and random arrays of points is outlined. The diffraction patterns of two‐dimensional models are compared with patterns from ideal crystals, imperfect crystals, and paracrystalline lattices. The effects of various types of crystalline imperfections and paracrystalline order on the diffraction pattern are analyzed and examples are presented. It is shown that both natural and synthetic polymers can be treated as paracrystalline materials. The diffraction patterns of polyethylene after various thermal and mechanical treatments are discussed. A detailed model of the structure of polyethylene is presented and various features of the structure of other polymers are pointed out.

ISSN:0021-8979    

DOI:10.1063/1.1729085

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

X‐ray diffraction from single crystals of polyacrylonitrile shows that the diffuse nature of the nonequatorial scattering maxima cannot be accounted for by crystal size. The theory of paracrystals may be used to set both an upper and a lower limit to the amount of lattice distortion and yields a plausible explanation for the absence or extreme weakness of higher‐order reflections. Finally, it is shown why the diffuse maxima cannot be used directly in measuring lattice parameters and the method which must be used to obtain a more definite crystal structure for polyacrylonitrile is indicated.

ISSN:0021-8979    

DOI:10.1063/1.1729086

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The theory for the scattering of light by homogeneous spheres satisfying the Rayleigh‐Gans approximation is extended to include the effect of heterogeneous density within the spheres. These internal heterogeneities are described by a Debye‐type exponential correlation function. The resulting scattering consists of a sum of two terms: one representing the homogeneous sphere scattering contribution and the second representing the additional contribution to scattered intensity arising from the internal heterogeneities. The predicted scattering patterns bear similarities to the experimentally observed scattering patterns obtained for spherulites of high polymers.

ISSN:0021-8979    

DOI:10.1063/1.1729087

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Liquid crystals offer a unique opportunity for physical studies. The nematic mesophase is an aggregate, yet fluid state, which consists of anisometric, rodlike structures. The flow of three nematic‐forming compounds,p‐azoxyanisole, anisaldazine, andp‐anisal‐p‐aminoazobenzene, was studied in both their isotropic and anisotropic states. Studies were made with capillary viscometers and with a high‐shear concentric cylinder viscometer. New density, coefficient of expansion, and transition temperature data are also given. The instrumentation used is described. The results add definition to the viscosity and density anomalies at nematic‐isotropic transitions. The data forp‐anisal‐p‐aminoazobenzene are entirely new. Values for anisaldazine establish previous viscosity and density results on an absolute basis. New results onp‐azoxyanisole contribute a temperature and shear rate extension to previous studies.

ISSN:0021-8979    

DOI:10.1063/1.1729088

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The flow properties of three cholesteryl esters have been studied in both their liquid crystal and isotropic ranges. Tests were made with low‐shear capillary viscometers and with a high‐shear rotational concentric cylinder instrument. Measurements on cholesteryl acetate are compared with relative viscosities given by Ostwald. Ostwald's viscosity data on cholesteryl propionate and butyrate are reevaluated. New flow data are also given for cholesteryl palmitate and stearate. Viscosity and flow activation energy are reported as a function of temperature, shear, and ester molecular weight. Results indicate that all cholesteryl esters show Newtonian flow in their isotropic states and non‐Newtonian flow in their respective cholesteric liquid crystal phases. New transition temperature and density data are also given for the three esters. These values and earlier density data for the benzoate ester are discussed in terms of the aggregate size of liquid crystals. Comparisons are made between the major types of mesophase.

ISSN:0021-8979    

DOI:10.1063/1.1729089

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Wide‐line nuclear magnetic resonance (NMR) studies have been made as a function of temperature and the angle between the stretch direction and the magnetic field on one‐way stretched poly (ethylene terephthalate) film. The data obtained were consistent with a structural model, the important features of which are the directions of the lines between interacting methylene and aromatic protons relative to the stretch direction. Evidence for planar orientation in one‐way stretched poly (ethylene terephthalate) film was obtained from wide‐line NMR data which were taken as a function of the angle between the normal to the film surface and the magnetic field. A difference of approximately 25°C has been observed in the temperature at which the sharp component appears in annealed, unoriented poly (ethylene terephthalate) film and powder phase material from the solid‐phase buildup reaction. This difference is explained as being due to a difference in the degree of crystalline perfection.

ISSN:0021-8979    

DOI:10.1063/1.1729090

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The fracture surface energy of a material can be obtained by the cleavage technique, in which a crack is propagated along the median plane of a strip sample by forces applied at the free ends. Unfortunately, the stress distribution in a conventional sample is such that the crack tends to deviate from its original direction, so that, for isotropic materials, external constraints must be imposed to overcome this tendency. To interpret the data, relations have been derived, based on the assumption that simple beam theory can be applied to the system; this assumption is not strictly valid. The use of the constraints can be avoided by machining fine slots along the opposing faces of the sample, and the system can then be analyzed by a direct and unambiguous method. The modified technique has been applied to the glassy polymers poly(methyl methacrylate) and polystyrene for which comparative data are available from both tensile and cleavage experiments.

ISSN:0021-8979    

DOI:10.1063/1.1729091

出版商:AIP    

年代:1963

数据来源: AIP