| Abstract: | It is shown that, on cooling, solvent present at the surface of swollen vulcanizates freezes before the onset of freezing in the gel solvent, causing gel solvent to diffuse to the sample surface where it adds to existing crystalline areas. At the freezing point of the gel solvent a liquid-solid equilibrium does not exist, and a theory is postulated to account for the freezing point depression observed in swollen gels in terms of the conditions required for the formation of crystalline nuclei within the gel solvent. The theory is shown to apply to the freezing of cyclohexane and benzene in vulcanized and unvulcanized natural rubber. In line with the theory the presence of carbon black does not alter the solvent freezing point, but vacuole formation around nonreinforcing fillers leads to lower freezing point depressions. |
