Abstract
Sorption of liquids by elastomers is advanced as a means of studying polymer structure. Liquids represent a wider versatility in this regard over vapors since they allow choices of molecular sizes, shapes, and configurational distributions, and thermal effects not available with vapors. Configurations, coiling versus stretched‐out molecules, are examined and shown to be of considerable importance in the sorption process. The problem of determination of the concentration dependence is attacked by use of a binary solution as a sorbent or swelling agent. The binary solution is so chosen that one liquid may be considered the solvent and the other liquid a nonsolvent for the particular elastomer. The ternary solution of butyl network—hexane—acetone was used in sorption experiments at 25°C. The total uptake of the binary liquid was measured from zero time to equilibrium in an optical swelling apparatus. Simultaneously, the composition of the binary liquid sorbed at any time was measured in a recording differential refractometer. The two sets of data were combined to calculate the ratio of the two liquids sorbed. The dilution procedure succeeded in varying the apparent activity of the solvent hexane. Preferential sorption of hexane was observed, but significant amounts of the nonsolvent acetone enter the network. The known equilibrium uptake values of hexane from the binary solutions are used to determine the concentration dependence of the diffusion of liquid hexane in a butyl network at 25°C. D~0~ = 2 × 10^−9^ cm.^2^ sec.^−1^ and a concentration dependence of 10 were obtained by this method. “Activities” for the hexane in the diluted form are calculated for an elastically calibrated network. The activities for the entire concentration range studied agree well with those of a comparable swollen polymer—liquid system such as natural rubber—benzene vapor. Test of the generality of the present method is suggested. Such a test would involve examination of the dependence of the hexane activities so calculated on the nature of the nonsolvent used in the binary liquid.