Abstract
It is already known that many rubber-like substances such as elastic sulfur and polyphosphornitryl chloride show crystal interferences when stretched, and that these interferences disappear again when the tension is removed. This shows that the melting point is increased by traction, and von Susich actually determined roentgenographically the relation between the melting point and deformation and thus obtained a “fusion curve.” This phenomenon can be explained by means of the kinetic theory of the elasticity of rubber. According to this theory, the stress set up in rubber when stretched depends on the fact that heat motion tends to restore to the statistically favorable, crooked, and hence shorter form, the primary valence chains which have been extended by traction and thus are in a statistically less probable position and form. For, as a result of free rotation, it is possible to have many curved forms but only one maximum elongated form; the thermodynamic probability β, and on account of the relation: S=R ln β, the entropy S as well, are consequently greater in the unstretched than in the stretched state.