摘要:

Six polyethylenes which differed widely in the degree of crystallinity were studied. The crystallinity was determined from density measurements. Both the density and the dynamic mechanical measurements were made over the temperature range from 25°C to above the melting point of the material.The dynamic shear modulus drops rapidly as the melting point is approached. The mechanical damping goes through a maximum near 60°C and then through a minimum just below the melting point. It is possible to predict the density of any of the polyethylenes at any temperature below the melting point from the value of the shear modulus at the same temperature. The more crystalline materials have the higher shear moduli and the higher melting points.

ISSN:0021-8979    

DOI:10.1063/1.1721531

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The dynamic bulk modulus of a high molecular weight polyisobutylene is calculated from measured longitudinal‐wave and shear moduli. A viscous or energy‐dissipating process associated with pure volume deformation is found, which appears to be a relaxation process. The peak in absorption of the shear and bulk moduli and the apparent activation energies associated with the two types of deformation are at least approximately the same, suggesting that the fundamental molecular mechanism involved in the two types of deformation may be the same.

ISSN:0021-8979    

DOI:10.1063/1.1721532

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The actual width of the proton resonance line in uncured natural rubber has been determined at room temperature to be 0.06 gauss. Curing of polymers increases the line width at a given temperature. The small increase in natural rubber is possibly compatible with a physical bonding rather than the usually assumed cross linking. For a butadiene‐styrene copolymer the increase in line width due to cure is somewhat larger. Carbon black loading increases the line width to a lesser degree than cure. This is compatible with the concept of physical bonding between the blacks and the polymer chain molecules. Variations in line width caused by changes in chemical composition and copolymerization were also investigated. Polypropylene and polypropylene oxide of roughly the same average molecular weight are compared. The polypropylene oxide exhibits a greater degree of ``rotation'' about its C&sngbnd;O bonds than polypropylene does about its C&sngbnd;C bonds. Two butadiene‐acrylonitrile copolymers also have been studied as a function of temperature. Finally, spin‐lattice relaxation timevstemperature studies are reported for a butadiene‐acrylonitrile copolymer and for raw butyl, over the temperature range from −‐50°C to 70°C. Estimates of the magnitude of the barriers hindering ``rotation'' are made.

ISSN:0021-8979    

DOI:10.1063/1.1721533

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The molecular orientation in polystyrene monofilaments can be determined by measuring the optical double refraction, or birefringence, which the orientation produces. When the oriented filaments are observed with monochromatic light under a polarizing microscope, a pattern of interference fringes is seen which can be analyzed. The general theory of this interference pattern is discussed, including consideration of the molecular basis of optical birefringence in polystyrene. Reversals of fringe order in the interference pattern can occur, but this complication can be handled by suitable methods. A number of experimental techniques useful in these studies are described. It is found that the birefringence is greater near the outside surface of the filaments than in the center, and this can be understood in terms of the rate of cooling during the orientation process.

ISSN:0021-8979    

DOI:10.1063/1.1721534

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Orientation and birefringence in linearly oriented amorphous polymers are discussed with particular emphasis on polystyrene type chains. A system of completely uncoiled parallel zigzag chains is defined as 100 percent orientation. The variation of birefringence with orientation is assumed to follow the same expression as that for the variation of polarization anisotropy with extension for a single random coil chain. With these assumptions and reasonable models for the completely uncoiled polystyrene chain it is possible to express any given birefringence as a percentage orientation.Methods are developed for the experimental determination of the birefringence at a particular point in an oriented monofilament instead of the usual determination of an average birefringence through the monofilament. The application of these methods to actual examples leads to reasonable values of the orientation.

ISSN:0021-8979    

DOI:10.1063/1.1721535

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A simple method is presented for the calculation of the transformation matrices between the Legendre polynomial expansion coefficients of the scattering cross section in the laboratory and center‐of‐mass systems. Approximate expressions for the matrices are given. Applications to transport problems involving the elastic scattering of neutrons are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721536

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Spurious maxima are frequently observed in pole figures determined by x‐ray diffraction techniques employing the Geiger‐counter spectrogoniometer. Their origin must be fully understood in order to avoid misleading interpretations of the pole‐figure data. By making film patterns and by the balanced filter technique—in each case with the specimen oriented for the appearance of one of the spurious peaks—these spurious maxima can be identified as diffraction of a component from the white radiation by a strongly diffracting (hkl) plane, and at a 2&thgr; angle corresponding toKadiffraction from the (hkl) plane under investigation. Spurious (110) and (112) peaks of this type may be observed in the (200) pole figure of iron and its alloys; spurious (111) and (220) peaks may appear in the (200) pole figure of face‐centered‐cubic metals such as nickel. These cannot be completely suppressed by filtering the Mo radiation used or by modifying the operating conditions such as tube voltage, spectrometer resolution, or counter type. Spurious (101¯1) peaks may appear in the (0002) pole figure of titanium and zirconium as the result of CuKadiffraction, and they can be avoided by increasing the resolution of the slit system.

ISSN:0021-8979    

DOI:10.1063/1.1721537

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The radiation patterns of prolate spheroidal conductors, excited by an electric dipole in its tip, are calculated, for a number of spheroids of varying thickness, the wavelengths being equal to roughly &pgr;, &pgr;/2, and &pgr;/3 times their major axes.

ISSN:0021-8979    

DOI:10.1063/1.1721538

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The principle of virtual work was employed to determine the stress distribution in a wood plate subjected to a load distribution such as to effect a uniform displacement in theydirection.The displacementualongx=±adeveloped an unexpected contour. The average value ofuappears to occur near the ends. This cautions against the common practice of placing the instruments for measuring Poisson's ratio near the middle. In the case of isotropic material the unexpected contours still prevail but are barely perceptible.The work was carried out for a fourth approximation (not presented) with sufficient accuracy to assure that the same contour was developing. These unexpected results were first observed in the laboratory of the U. S. Forest Products Laboratory, Madison, Wisconsin—an experience which prompted this theoretical confirmation.

ISSN:0021-8979    

DOI:10.1063/1.1721539

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

It is shown, under fairly general conditions, that the standard deviation of the residuals of the straight line fitting a set of points with uniformly spaced abscissas by the method of averages is at most2/3times as great as the standard deviation of the least‐squares line. Theorems of significance in the practical use of the method of averages are proven in the course of the analysis.

ISSN:0021-8979    

DOI:10.1063/1.1721540

出版商:AIP    

年代:1954

数据来源: AIP