The journey of tuning chitosan properties in colloidal systems: Interactions with surfactants in the bulk and on the alumina surface

Abstract

The specific physico-chemical properties of chitosan (Ch), a biopolymer isolated from chitin, and its impact on the stability of colloidal dispersity have focused the interest of science and industry. However, in some cases chitosan alone is not enough to provide high stability to dispersions, making it necessary to add surfactant to the chitosan/oxide system, leading to superior stabilizing properties due to the association of polymer and surfactant molecules to form complexes that can modify the ability of bare chitosan for adsorbing on colloidal materials. This study explores the interactions between chitosan and alumina in the presence of three different anionic surfactants: the hydrocarbon SDS (sodium dodecyl sulfate), the fluorocarbon FS-91 (Capstone® FS-91), and the silicone A-Si (Silphos A-100). Different analytical methods evidenced chitosan adsorption on the alumina surface, forming hybrid organic–inorganic materials. This process can be enhanced by adding surfactant, with SDS leading to a strong increase of chitosan adsorption. Elemental mapping and scanning electron microscope imaging have provided a confirmation of the co-adsorption of polymer and surfactant on the alumina surface. The latter emerges as a very important finding because the results have shown that small quantities of surfactant (as low as 0.002% v/v) can strongly influence the adsorption and stability of multicomponent colloidal systems. This allows decreasing the chitosan amount required for the enhancement of the colloidal stability in relation to dispersions without added surfactants, providing the basis for reducing the production costs of colloidal dispersion, which opens new opportunities to chemical industry