Freezing point depression of gels produced by high polymer network

Abstract

Abstract Weakly vulcanized rubber swollen in benzene for one or several days forms a gel whose freezing point is about 5°C. lower than the freezing point of the solvent with which the gel is in equilibrium. This anomaly of the freezing point depression is to be explained by the three‐dimensional network present in the gel, which mechanically prevents the formation of macroscopic crystals. The phenomena observed in the benzene system are compared with similar observations made recently in the case of aqueous gels of polyvinyl alcohol and polyacrylic acid. The benzene system differs from the aqueous system in that an undercooling is observed in the benzene system as well for the formation of crystals outside at the surface of the gel as for the formation of crystals inside the gel. Furthermore, in the case of the benzene system at temperatures below the freezing point of pure benzene a transport of solvent from the inside to the outside of the gel takes place, i.e. a freeze‐drying of the gel is observed. These differences in the behavior of the aqueous and benzene systems are understood as being due to the volume dilation connected with the crystallization of water and the volume contraction occurring in the case of crystallization of benzene. The anomaly of the freezing point depression is a means of characterizing the width of ultramicroscopic structures present in high polymer, essentially also in biological systems.