from abstract ideas...fundamental knowledge at Esso Research
Adsorption rather than diffusion may be the controlling mechanism in the transport of liquids through elastomers. This new hypothesis is supported by evidence obtained by Esso Research scientists using a novel photo shadow method for continuous measurement of swell in elastomers. As a result of these fundamental studies, more intimate knowledge of structure and increased understanding of segmental motion may make possible more precise predictions of polymer behavior. Increasing the cross-link density in an elastomer network appears to de-
crease the diffusion coefficient to an extent not predicted by the diffusion theory. Observations also show the seeming contradiction that increasing the path length with immobile obstructions, in the form of a variety of carbon black particles, also increases the apparent diffusion rate 2.5 times. Re-examination of well known equilibrium uptake data poses such questions as: W h y does a butyl r u b b e r vulcanizate sorb twice as much cyclohexane as n-hexane when the latter has a much more flexible structure? How does a butyl elastomer distinguish be-
tween the flat plate structure of benzene and the chair structure of cyclohexane whereas natural rubber does not? Critical experimentation, together with m a t h e m a t i c a l studies, have strengthened the thesis that the solvent molecules pass into the elastomer by successive adsorption on successive planes. T h e elastomer chains appear to play an active role in the transport process rather than the passive one required by diffusion. . . . adapted from a scientist's notes at Esso Research and Engineering Co., P.O. Box 45B, Linden, N. ].
