The Interaction between Rubber and Liquids. VI. Swelling and Solubility in Mixed Liquids

Abstract

Abstract The equations derived in the previous paper for the osmotic equilibrium between a ternary mixture of polymer + two liquids and a mixture of the two liquids are applied to the swelling of cross-linked polymers in mixed liquids and to the solubility of linear polymers in mixed liquids. A mixed liquid has solvent properties intermediate between those of its components only when these mix ideally. The larger the heat of mixing of the liquids, the greater is the solvent power of the mixture relative to those of the components. This conclusion forms the basis of an explanation of the enhanced swelling of rubbers in pairs of dissimilar liquids and of the fact that a mixture of two nonsolvents may be a solvent over a certain range of concentration. Experimental results are given for the swelling of vulcanized rubbers and the critical solubility limits of unvulcanized rubbers. It is shown that these can be explained qualitatively from the cohesive energy densities of the three components, and semiquantitatively from the measured heats of mixing of the three binary mixtures. The work described in these two papers forms a part of the program of fundamental research on rubber undertaken by the Board of the British Rubber Producers' Research Association.