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One-Dimensional Growth of Hydrogel by a Contact of Chitosan Solution with High-pH Solution

To clarify the mechanism of the gelation from a contact line between polymer solution and nonsolvent, we developed a theory for the dynamics of the gel formation from one side of a rectangular cell and compared it with that for cylindrically symmetrical boundary condition. The growth of the gel layer thickness was expressed by a scaled integral equation having the same coefficient Kin expressing the contribution of initial concentrations of solvent and nonsolvent for both boundary conditions. To confirm the theoretical results, the time course of the gel layer thickness was measured using the system chitosan in aqueous acetic acid as polymer solution and sodium hydroxide aqueous solution as nonsolvent. The experimental data fit well to the theoretical equations, which indicated the validity of the theoretical assumptions and suggested a universal behavior irrespective of boundary condition. It is also shown that the effect of the interface tension is negligibly small. [Supplementary materials are available for this article. Go to the Publisher's online edition of Soft Materials for the following free supplemental resource(s): Addenda to II. Theory.]