It has long been suspected that if liquids were sheared sufficiently rapidly they would exhibit a shear elastic effect as well as a viscous effect. This supposition was verified recently by one of the writers (see reference 8) by employing a torsionally vibrating crystal and measuring the mechanical loading for the shear wave by observing the increased resistance at resonance and the change in the resonant frequency. By this method it was shown that long chain polymer liquids had shear configurational elasticities in the order of 10 7 dynes/cm 2 .The use of a torsional crystal is limited in frequency to about 2 to 3 X10 5 cycles on account of the small sizes needed. In the present paper the range of shear wave measurements in liquids has been extended up to 60 megacycles by observing the effect, on a series of shear waves in a fused quartz rod, of terminating the rod by a thin layer of a liquid. The shear wave in the rod is altered in magnitude and phase by the boundary layer impedance of the liquid. By observing the reflection loss and the change in phase caused by the liquid layer, a measure is obtained of the shear impedance of the liquid. By employing a fused quartz rod for which the shear wave strikes the reflecting surface at an angle from the normal of about 79 degrees, the effect of the shear wave impedance on the boundary is greatly enhanced and a more accurate measurement obtained.Both the torsional crystal and high frequency shear wave techniques applied to polyisobutylene and poly-a-methylstyrene liquids, show that there are two main relaxation frequencies in these liquids. At frequencies under 100 kc, the shear stiffness is in the order of 3X10 7 dynes/cm 2 , while in the high megacycle range it has increased to 5 X10 9 dynes/cm 2 . The low shear elasticity appears to be associated with a composite motion of molecular rotation and translation that allows a configurational change to occur from the most probable chain shape. When the shear stress is removed, the molecule quickly returns to its most probable shape. This results in a low shear stiffness. At high frequencies this motion cannot take place, and the shear stiffness is determined by motions within single potential wells, and the value approaches that for a crystal. It is shown that the dispersion for longitudinal waves measured recently (see reference 11) is primarily due to the shear mechanisms investigated. L INTRODUCTIONI T HAS long been suspected that if liquids were sheared sufficiently rapidly, they would exhibit a shear elastic effect as well as a viscous effect. In fact, Maxwell, 1 on the basis of a gas model, predicted that an instantaneous shear distortion would have a relaxation time r and a relaxation frequency jv given by the formulas T = r}/n\ / r ==l/(27rr)=M/(27n?),(1) where t\ is the shear viscosity and \x the shear elasticity. A similar result has recently been obtained by Frenkel 2 by assuming that a liquid has a short range order similar to a solid, and identifying the relaxation time r as the mean life in a sedentary stat...
Divinylbenzene (48%)/ethylvinylbenzene copolymer was converted to a series of pyrolytic derivatives. Enough of the carbon bond network remained intact throughout thermal rearrangement and condensation to retain the original gross shape of the copolymer in the final polymer carbon. Although a carbon residue (6% by weight) was obtained by direct heating of the copolymer, yields were increased eightfold by preoxidation or prechlorination. Such an alteration of thermal degradation is obviously a complex process involving both “inhibition,” in the ordinary sense, and a considerable contribution toward an increased valence network density. As a consequence, the average molecular weight of volatile fragments evolved during carbonization is inversely proportional to the oxygen content of the original hydrocarbon polymer. Pyrolysis of divinylbenzene copolymer, containing 18% oxygen, resulted in a 50% volume shrinkage, 50% weight loss, and a 100% density gain. Unless these data are attributable to extensive microporosity, it is difficult to account for the sorption of up to 3 cc. of helium gas per gram of polymer carbon at 30°C. and 600 mm. pressure; and calculated surface areas as large as 1400 sq.m./g. Abrupt changes in the progress of polymer carbon formation occurred between 600 and 700°C. The residue became rigid; vigorous evolution of volatile products, principally hydrogen, suddenly diminished; and paramagnetic resonance absorption (unpaired electron concentration) dropped about tenfold while d.c. resistivity decreased 106 ohm cm. In this region, also, x‐ray patterns were most diffuse, exhibiting no maxima characteristic of carbon scattering in either hydrocarbons or condensed rings. Finally, the x‐ray patterns of polymer carbon intermediates became less diffuse in samples prepared at 700°C. or above. Yet, scattering indicated the presence of crosslinked graphitic layers of such stability that reordering or true graphitization did not occur at 2400°C.
Dielectric Properties and Structure of Linear Polyamides 2171 120°t emperature range for one) for the frequency interval 1 kc. to 75 me. These macromolecular chain polymers are of known structure and composition, so that the observed polarization and dispersion were related to the orientation and concentration of polar groups in the chains and to their relative positions in adjacent chains. The dielectric constants, e', of all of the polymers exceed the refraction value even at room temperature. The oscillation of individual dipole groups (ester linkages) contributes the orientation polarization. These dipoles interact somewhat along a given chain, but chiefly between chains, to cause the observed broad dispersion. The polyesters exhibit principally high frequency absorption, with maxima at low temperatures. This supports the concept of small oscillating units in the chains, in agreement with the observed activation energy of orientation.The packing of the chains is strongly influenced by the dipoles and the formation of dipole layers makes the interaction, which contributes to dielectric absorption, largely independent of polar group concentration.The dielectric results reveal thermal motion in the polymers. These chain oscillations are supposed to account for mechanical properties such as thermal retraction associated with chain kinking in long chain molecules. Murray Hill, N. J.
In the case of dodecylamine hydrochloride the conductivity rises in the third range in spite of greatly increased viscosity.5. The values of A0 and lc have been determined from the experimental data. Chicago, Illinois
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