A. M. Bueche

Scattering by an Inhomogeneous Solid

A general treatment of the scattering of radiation by an inhomogeneous material is developed. It is shown how scattering measurements can be used to obtain the average square of the fluctuations in refractive index or electron density and a correlation function which measures the degree of correlation between two fluctuations as a function of their distance of separation.The scattering of visible light by Lucite and two glass samples has been investigated. The data are analyzed in terms of the quantities mentioned above. It is found that the extensions in space of the inhomogeneities in the Lucite sample are much greater than those in the optical glass samples investigated. The magnitudes of the fluctuations in refractive index are found to be dependent on the composition of the sample.

Intrinsic Viscosity, Diffusion, and Sedimentation Rate of Polymers in Solution

Intrinsic viscosity, diffusion and sedimentation rate of polymers in solution is calculated by a generalization of Einsteins theory for impermeable spheres. For the coiled polymer molecule a sphere is substituted which hinders the liquid flow through its interior only to a degree depending on the average density in space of the polymer molecule in solution. The amount of shielding of the liquid flow which is introduced in this way determines the exponent in the customary exponential relation between intrinsic viscosity, diffusion, or sedimentation rate and molecular weight. This relation is shown to have only the merits of an interpolation formula. It is shown how the dimensions of the molecular coil can be derived from the experimental data on viscosity, and these dimensions are compared with those derived from interference measurements. The point is stressed that the relation between intrinsic viscosity and molecular weight is rather indirect and depends essentially on the type of polymer molecule unde...

Theory of Rolling Friction for Spheres

A theory of rolling friction featuring the importance of elastic hysteresis losses is presented. A simple model of retarded elasticity is chosen to represent the physical properties of the material. A prediction resulting from the theory is that the coefficient of friction for a relatively hard sphere rolling on a softer base material should vary with speed so as to go through a maximum. This relationship resembles closely the variation of mechanical loss with frequency.The results are not restricted to rolling but also apply to well‐lubricated sliding where shearing forces have been minimized. Although the theory is developed for a material with idealized physical properties, it nevertheless affords a basis for comparing real materials and for predicting their frictional properties in cases where deformation losses are predominant.

Light Scattering by Concentrated Polymer Solutions

The light scattered by benzene solutions of polystyrene up to a volume fraction of polymer of 0.62 has been measured. The results are compared with what was to be expected on the basis of recent thermodynamic theories for polymer solutions.This comparison has led to the recognition of a new and rapid method for estimating molecular weights. The method also seems to be a convenient one for obtaining thermodynamic information.

Stress Relaxation in Elastomers

The process of chemical stress relaxation in elastomers is examined in some detail. It is predicted that in some cases it will be possible to determine the location of the chemical bond broken. The special cases of relaxation due to scission of cross links and random scission of the polymer are calculated. The shapes of the stress vs time curves are widely different.

Kinematographic Study of Tensile Fracture in Polymers

High speed motion pictures were taken of silicone rubber, irradiated polyethylene, Plexiglas II, and aluminum foil while they were being broken. Fractures started internally in some of the silicone samples but at the edges of all of the others. The rates of crack growth and the rates of retraction of the ends of the rubber samples were measured. The velocities with which the cracks grew were compared with the results of the theories of Poncelet, Yoffe, Mott, and Roberts and Wells. Their prediction, that the velocities should be about one half those of transverse waves in the media, was found to represent the data for materials with moduli differing by five decades. After fracture, the ends of the rubber samples contracted with velocities approximately equal to the velocities of longitudinal waves in these samples.

Investment in innovation

This paper reviews briefly the importance of the U.S.investment in innovation. It then reiterates some of the statistics that support a growing concern related to the declining growth rate of innovation. The importance of business investment in the innovation process is identified as a key element in economic progress. Several charts and graphs are used to illustrate this point. Factors that influence investment are discussed. Finally specific recommendations are made that should be considered by both the public and private sectors.

Energy Conservation, Efficiency and Substitution

The US has failed to make a serious reduction in oil consumption because, unlike other western countries, the US has not made a national commitment to develop alternative energy sources. Energy costs, as a result, are no longer in equilibrium with the gross national product. A proposal to replace oil with electricity in five end-use applications is possible with present technology and, in most cases, with available products. The suggested end uses are residential and commercial space conditioning, low-temperature industrial and commercial heat, high-temperature industrial direct heat, intracity passenger and freight transport by bus and van, and high-density rail transport. Other opportunities are substituting electricity or coal for gas and repowering oil-fired power plants to burn coal. Low-cost and cost-effective options should be taken first and should concentrate on replacing oil and on the costs of changing the energy systems. (DCK)