Strontium-Induced Gelation of Sodium Alginate in the Presence of Carbon Nanotubes: Elemental Analysis and Gel Structure

Abstract

The elemental composition and structural features of the junction zones of a strontium–alginate hydrogel and their alteration under the intercalation of multi-walled carbon nanotubes into the hydrogel structure were studied. It was shown that the crosslinking with Sr2+ cations due to electrostatic interactions leads to the association of polymer chains into junction zones with incompletely filled cells. It was found that in strontium alginate, the average cell occupation number of Sr2+ cations is less than 1 and approximately equal to 0.64. In nanocomposite hydrogels including multi-walled carbon nanotubes, its increase to 0.81 indicates the appearance of a more ordered structure of alginate chains in junction zones. The information about the most preferred types of egg-box cells for binding with Sr2+ cations was analyzed. The existence of Sr2+ cations in nonequivalent positions was established. The possibility of separating the contributions of chemical adsorption due to ionic bonds with alginate chains and physical adsorption due to the appearance of local energy minima near alginate chains, leading to the appearance of ordered secondary structures, was demonstrated. It has been shown that the addition of carbon nanotubes to a hydrogel changes their sorption capability, leading, first of all, to an increase in the possible sites of physical adsorption.