(342f) Structural Growth and Viscoelastic Properties of Polysaccharide Layers in Mono- and Divalent Salts

Understanding the adsorption properties of polysaccharides in terms substrate affinity, kinetics, and layer structure is of paramount importance in industrial and natural systems. The structural growth of the layers of two model polysaccharides, sodium alginate and polygalacturonic acid, was characterized by quartz crystal microbalance with dissipation (QCM-D). Monitoring the variations in frequency and dissipation energy provides insights into both the average adsorbed mass and the viscoelastic properties of the adsorbed layer of polyelectrolytes along with the associated ions and water molecules. Both polysaccharides have similar adsorption patterns with increasing ionic strength and showed significant complexation capacities in presence of calcium ions. The normalization of the dissipation by the frequency change due to macromolecule adsorption demonstrates that the viscoelastic properties of the layer vary as a function of the ionic strength and polysaccharide type. QCM-D measurements were supplemented by force measurements between the adsorbed polysaccharide layer and carboxylated colloidal probe via AFM. The results are discussed in terms of the variations in molecular structure, configuration, and compressibility of the adsorbed layer as a consequence of shielding of the polyelectrolyte charges with increasing ionic strength and calcium binding to polysaccharide functional groups.