(713f) Gel and Capillary Formation Dynamics in Cation-Mediated Gelation of Alginate Observed by NMR Methods

Nuclear magnetic resonance (NMR) relaxation, pulsed field-gradient and imaging measurements are applied to observe the formation of alginate gels from sodium alginate and solutions of copper and calcium chloride. Images of the formation process show expected macroscopic front formation and motion (1) while the relaxation and pulse field gradient (PFG) measurements provide information on the structure of, and dynamic molecular phenomena occurring at, the gel front. Gels formed with mixtures of calcium and copper ions show two regions of gel formation. The extent and features of these regions can be explained by a reaction-diffusion model that includes competition between calcium and copper ions for sites in the gel. As the initial ratio of copper to calcium in the ion solution increases, the number and density of capillaries increases while their size decreases. Pulsed field-gradient measurements at and near the gel front were not found to be consistent with the roll-cell velocity model currently proposed as the capillary-formation mechanism in these systems (2). The NMR measurements suggest an alternative view of the gel and capillary formation processes in these systems in terms of a dynamic phase transition.

References

1. Potter, K, BJ Balcom, TA Carpenter and LD Hall, Carbohydrate Research, 257(1994), 117. 2. Treml, H, S Woekli and H-H Kohler, Chemical Physics, 293(2003), 341-353.