NMR studies of calcium-induced alginate gelation. Part I?MRI tests of gelation models

Magnetic resonance imaging was used to monitor the one-dimensional space–time evolution of the gelation of a sodium alginate solution by the ingress of calcium ions. The data were compared with theoretical reaction–diffusion models of the gelation process. Good agreement was found for short-time behaviour but deviations appear at longer times, most probably owing to the onset of syneresis. Fitting the short-time behaviour showed that the mean number of calcium ions per alginate monomer in the gel is constant but that the gelation rate constant apparently decreases with diffusion time. The possible reasons for this are considered.