Interfacial dilational rheology of chitosan-silica nanocomposite films at the aqueous dispersion/air interface

• Stable chitosan-capped nanoparticle dispersions form at high and low chitosan:silica concentration ratios. • Chitosan-silica synergy enhances the reduction of the water/air interfacial tension. • Chitosan-silica layers display predominantly elastic behavior at water/air interfaces. • High chitosan concentration improves nanoparticle adsorption at the interface. This study investigates the interaction between positively charged chitosan and anionic hydrophilic silica nanoparticles in aqueous media, resulting in the electrostatic formation of chitosan-capped silica nanoparticles. Optimal conditions for the formation of stable dispersions were determined, highlighting that the adsorption of chitosan on silica nanoparticles, as well as its solubility, is enhanced in acidic medium (pH = 4.5). Electrophoretic mobility measurements confirmed the positive zeta potential of chitosan-capped particles, indicating charge inversion due to chitosan adsorption on negatively charged silica surfaces. Adsorption at the dispersion/air interface significantly reduces the interfacial tension, with a synergistic effect observed between chitosan and silica. Capillary wave experiments demonstrated the formation of viscoelastic layers with the dilatational elastic modulus of the nanocomposite layers exceeding their viscous modulus. The frequency dependence of the interfacial dilational moduli showed that increasing particle concentration enhanced the viscoelastic properties of the interface. This study provides novel insights into the dilational rheological response of chitosan-capped silica nanoparticle layers, revealing the interplay between surface charge neutralization, adsorption dynamics, and the viscoelastic properties of the interface. The results suggest potential applications in the stabilization of liquid and solid foams and highlight the importance of chitosan-capped particles in modifying water/air interface properties and improving the rheological behavior of particle-laden interfaces.