Formation kinetics and rheology of alginate fluid gels produced by in-situ calcium release

The formation and properties of alginate fluid gels produced using in-situ calcium release and a defined shear field are investigated.

Results show that, while the rate of particle growth during formation increases significantly upon lowering the shear rate, the rate of inter-particle interaction post-production remains unaffected by the magnitude of shear.

The longer polymer chain allows a greater number of possible sites for calcium crosslinking per chain which enhances the formation of a percolating network and increases the number of rheologically-effective network crosslinks. As a result, high M_w alginate fluid gels exhibit faster gelation kinetics and greater viscosities than those of low M_w alginate fluid gels.

Particle stiffness increases with increasing CaCO₃ concentration until a critical value is reached. Quiescent gels display the same CaCO₃ critical value, suggesting that the number of crosslinks within an individual fluid gel particle is equivalent to that of their counterpart quiescent gel. This is due to the fast coil-dimer transition which, under the applied shear field, leads to kinetically trapped fluid gel structures. However, their textural response differs from that of a quiescent gel which is likely caused by the bridging between fluid gel particles.

In addition to advancing the understanding of the production of fluid gels from alginates, this work shows for the first time how the ordering kinetics and the resulting particle properties can be manipulated by the choice of alginate M_w and CaCO₃ concentration, potentially allowing the design and delivery of specific structures with desirable attributes.