An analysis of anisotropic gel forming process of chitosan

We have prepared anisotropic chitosan gels with birefringence by immersing a sandwiched chitosan in aqueous acetic acid into aqueous sodium hydroxide. The gel forming process was traced under observation with crossed nicols and open nicols with and without litmus agent. The time courses of the gel front, the birefringent layer and the pH-change layer agreed with each other fairly well. The early stage of the dynamics was expressed by a theory with an assumption of an OH^- diffusion-limited process, whereas the behavior in the late stage deviated from the theoretical one. The deviation results from the effect of the outflow of protons, and the crossover of the two behaviors is attributed to the relaxation to the thermal equilibrium.