Phase relationship and dynamics of anisotropic gelation of carboxymethylcellulose aqueous solution

Anisotropic gelation of carboxymethylcellulose (CMC) in aqueous NaOH sandwiched between two circular cover glasses by immersing it in aqueous CaCl₂ has been studied. In the course of dialysis, gelation and phase separation occurred simultaneously to make turbid stripes arranged radially. The time course of the gel layer width was well expressed in scaled linear plots predicted by a theory based on "moving boundary picture" at low CMC concentrations. On the other hand, at high CMC concentrations, the time course was expressed by a two-stage dynamics. The time course did not depend on the initial thickness of the CMC solution and the diameter of the cover glasses, whereas the rate of gelation decreased with increasing CMC concentration. It was attributed to the change in the calcium cation concentration required for forming the gel in the process. The universality and the individuality of the present system in the gelation dynamics are discussed.