Figure 6: Zeta potential as function of time (n=9) with corresponding pH/Ca²⁺ curve.

Morphologies (1=polymeric assemblies, 2=spherical nodules and 3=aggregated spheres) and structures (1=partially penetrable, 2=opaque spheres, 3=aggregate of opaque spheres), R, a and r are radii, ξ=hydrodynamic skin dept, and D_f,1, D_f,2 are fractal dimensions. Zeta potentials were measured in transmission at a 50 V effective voltage (average over 100 runs). The Von Smoluchowski equation⁵⁵ was applied, considering the high ionic strength used (I=0.2 M) and size of the polymeric aggregates (>100 nm). Importantly, for the described complexes the distances between the charged moieties inside the complex are not small with respect to the complex size and therefore their interactions deviate from the DLVO theory derived for larger colloidal particles⁵⁶. Hence, the ion-association complexes should not be regarded as particles with a central (negative) charge but as species with localized negative and positive charges that can interact with the opposite charges in neighbouring complexes, favouring their aggregation^57,58. The presence of high concentrations of Na⁺ counter ions will lead to a significantly reduced effective charge⁵⁹ further facilitating the interaction between the charged complexes⁶⁰.