On the percolation of alginate/calcium systems at low concentrations

The sol-to-gel transition of an alginate rich in β-d-mannuronic acid residues and at a concentration of 0.1% w/v in 15 mM NaCl in the presence of calcium ions of 0 to 3.5 mM was studied with dynamic light scattering. The dynamics of the different systems added further insight into the alginate gel forming mechanisms. Below a Ca²⁺ concentration of 0.7 mM, the build-up of small aggregates could be verified. Moreover, at a critical concentration, close to 0.9 mM Ca²⁺, a percolated, non-ergodic network started to form from some of these aggregates, with smaller aggregates still diffusing in the network. The system displayed strong non-ergodicy at high Ca²⁺ concentrations with a non-ergodicity parameter that appeared to form discontinuously from near zero to a clearly non-zero value at the critical Ca²⁺ concentration.