Index of content:
Volume 13, Issue 1, 01 January 1945
Publication of Papers from the Inaugural Meeting of the Division of High‐Polymer Physics of the American Physical Society13(1945); http://dx.doi.org/10.1063/1.1723963View Description Hide Description
13(1945); http://dx.doi.org/10.1063/1.1723966View Description Hide Description
Actual substances exhibit a very complicated behavior under mechanical stresses which cannot be described by classical elasticity theory nor by the classical theory of the hydrodynamics of viscous fluids. A general molecular theory describing the behavior of matter under stress is discussed and related to previous investigations and to experimental observations. Particular attention is devoted to rubberlike substances for which the classical theories are definitely inadequate. Experimental results on relaxation and creep of rubbers are interpreted in terms of modern structural concepts. It is found that these substances exhibit three regions of stress‐temperature‐time dependence. At intermediate temperatures there exists a region of relative stability in which the statistical‐thermodynamic theory of rubberelasticity is valid. At elevated temperatures relaxation and creep are caused by chemical changes involving the rupture and formation of primary valence bonds. These chemical changes, which are responsible for the aging of rubber, can be isolated and studied by appropriate experimental techniques. At low temperatures relaxation and creep are caused by the slipping of secondary interchain bonds which are breaking and reforming in times comparable to experimental times of measurement. Theories are advanced to explain the observed stress‐temperature‐time behavior of rubbers over the entire temperature range studied.
13(1945); http://dx.doi.org/10.1063/1.1723964View Description Hide Description
The rise of temperature on fast stretching of natural and synthetic rubber stocks was investigated recently by Dart, Anthony, and Guth (D.A.G.). Since then the experimental technique was considerably improved and the taking of data greatly simplified thereby. By D.A.G. emphasis was placed to record temperature rises of up to 15°C for extensions up to 700 percent by a fast galvanometer of moderate sensitivity. In the present work this high heat was investigated. In addition, however, a less fast but more sensitive galvanometer was employed to record changes of temperature as small as 0.001°C for 0–80 percent extension. In accordance with early work by Joule on natural gum (1859) it was found that also Butyl gum stocks show an initial cooling effect. This passes at a thermoelastic inversion point into a heating effect. In agreement with the recent theory by James and Guth the thermoelastic inversion point was found to depend solely upon the thermal expansion coefficient of the unstretched stock. The coefficient of thermal expansion was measured for Butyl stocks in the present work. Butyl tread stocks also show the thermoelastic inversion point. The work of D.A.G. showed that the rise in temperature on extension is a slowly rising function of the extension with a steep upward turn and almost linear continuation after the onset of crystallization. The samples were kept extended for a minute and then the cooling arising on retraction also measured. The negative of the cooling on retraction plotted against extension fall, according to the second law of thermodynamics as it should under the extension curve, but crosses it at the onset of crystallization. For Butyl gum stocks this crossing takes place at rather high (600 percent or more) extensions in agreement with x‐ray work. More similarity was found between Butyl and Hevea tread stocks than between the corresponding gum stocks. Loading shifts the onset of crystallization to a range of smaller extensions. In addition to measuring the change of temperature on extension and retraction, the residual rise in temperature after an extension and immediate fast cycle retraction was also observed. This quantity is a measure of internal friction in Butyl rubber and is closely connected with rebound and free vibration tests. Summarizing, the method described has a twofold application for development work: 1. Changes of the temperature on extension and delayed retraction indicate in a simple manner the onset and progress of crystallization. 2. Changes of the temperature in a fast cycle give an estimate for internal friction. Both these applications will facilitate attempts to improve present synthetics.
13(1945); http://dx.doi.org/10.1063/1.1723965View Description Hide Description
Published x‐ray data from crystalline selenium and tellurium and from stretched sulfur (amorphous), polyethylene, polyisobutylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidine chloride, polyoxymethylene, polyoxyethylene, polyethylene disulfide, polyethylene tetrasulfide, and polyphosphonitrile chloride are compared. In most cases the experimental identity distance in the direction of the chain axes and the expected interatomic distances and interbond angles are found to be in agreement with the assumption that the chain atoms form a regular spiral, unidirectional in each chain and of uniform pitch. Apparent exceptions are briefly discussed.
The Influence of Velocity Gradient on the Relation Between Viscosity and Concentration in Cuprammonium Solutions of Cellulose13(1945); http://dx.doi.org/10.1063/1.1723967View Description Hide Description
The numerous equations which have hitherto been employed to relate the viscosity of solutions of high polymers to the concentration of the solute have neglected to recognize explicitly the influence which velocity gradient (rate of shear) has upon the observed viscosity of non‐Newtonian liquids. Consequently, the theoretically important, intrinsic viscosity, calculated on the basis of these equations, from data obtained on a solution in the anomalous region, is found to have a different value for each velocity gradient prevailing during measurement. A modification of the Baker‐Philippoff equation has been developed empirically having the advantage that it yields a uniform value for the intrinsic viscosity of a given solution regardless of changes in velocity gradient. This new equation:has been found to agree well with data on cuprammonium solutions of cellulose in concentrations below 0.5 g per 100 ml. The parameter λ, interpreted as a function of velocity gradient, is found to increase with gradient, while ki , which is shown to be the intrinsic viscosity η i , is found to have a constant value characteristic of the solute. It appears that the second constant appearing in other recent equations in addition to the intrinsic viscosity, may be interpreted as a velocity gradient adjustment term. The algebraic series into which the various recent equations can be expanded to express η r are strikingly similar to each other and to a proposed equation based on the Eyring reaction‐rate theory.