New Aspects to Physicochemical Properties of Polymer Gels in Particularly the Coordination Biopolymeric Metal–Alginate Ionotropic Hydrogels

Abstract

Some coordination biopolymeric metal–alginate ionotropic hydrogel complexes were prepared by the replacement of the Na⁺ counter ions of alginate sol polysaccharide by monovalent silver(I) or polyvalent metal ions forming their corresponding complexes in either granule or hydrogel phases. The type of such phase and the capillary or non-capillary structures property were found to be dependent on the method of preparation and the direction of diffusion of the metal ion toward the alginate sol matrix whether is of upward or downward direction. The net process of exchange leads to the so-called sol-gel transformation to give its respective hydrogel complexes. This process takes place through formation of partially ionic and partially coordinate bonds between the metal ion and the carboxylate and hydroxyl functional groups of alginate, respectively. This kind of chelation forms a sort of bridges in an egg box-like structure. The anisotropic property of the hydrogels is owing to the orientation of the solvent molecules and macromolecular chains toward the chelated metal ions. The geometrical configuration and physicochemical properties of the hydrogel complexes depend on the nature of the metal ions such as the valence and its coordination number as well as on the strength of chelating of the bonds formed. The kinetics and mechanism of sol-gel transformation, electrical conductivity, and thermal decomposition with their evaluated kinetic parameters along with the other physicochemical properties such as FTIR, XRD, morphology, configuration geometry, and rheological properties have been investigated and discussed.

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