Showing papers in "Transactions of The Faraday Society in 1947"

The photo-elastic properties of rubber. Part I: Theory of the optical properties of strained rubber

Abstract: Abstract From the consideration of vulcanized rubber as a network of randomly kinked molecular chains, the optical constants corresponding to the most general type of homogeneous strain are derived. Under such a strain the rubber is shown to acquire the properties of an optically biaxial crystal, characterized by three principal refractive indices in the directions of the principal axes of strain. For directions of light propagation parallel to one of the principal axes, the birefringence is shown to be a simple function of the principal extensions and is, moreover, proportional to the difference between the two corresponding principal stresses. If the rubber is swollen with a liquid having the same refractive index as itself, the birefringence for a given state of strain varies inversely as the cube root of the swelling ratio, as do also the principal stresses.

The photo-elastic properties of rubber II. Double refraction and crystallisation in stretched vulcanised rubber

Abstract: From an investigation of the variation of birefringence, with elongation in vulcanized rubber extended at temperatures ranging from −50° to +100° C, it is possible to distinguish the effects of crystallization from the true strain-birefringence. The latter agrees closely with theoretical expectations in its dependence on stress and on elongation. The data do not permit of a quantitative estimation of the relative amounts of crystalline material present under various conditions. Experiments with stretched swollen rubber further confirm the theory and yield further evidence on the effects of crystallization.