Foam Stability Mediated by Cellulose Nanocrystal–Anionic Surfactant Interactions

The combination of cellulose nanocrystals (CNC) and anionic alkyl poly(ether) carboxylate surfactants offers a sustainable approach to modulating the interfacial and foaming properties of aqueous systems. This study investigated CNC-surfactant interactions in bulk and at the air-water interface using surface tension, interfacial rheology, foaming tests, particle size, zeta potential, and electron microscopy. CNC slightly increased the critical micelle concentration and reduced surfactant adsorption at the interface, indicating an interaction between the two components. Increasing the surfactant concentration improved CNC dispersion, forming smaller, more uniform aggregates. Although CNC addition slightly reduced foamability due to slower surfactant diffusion and increased surface tension, it significantly enhanced foam stability at low surfactant concentrations. This improvement was attributed to aggregated CNC forming percolated networks and reinforcing interfacial films. Dynamic surface tension and dilatational rheology confirmed an increased interfacial viscoelasticity, evidencing stronger interfacial layers. At high surfactant concentration, CNC was well dispersed, resulting in lower viscoelasticity and reduced foam stability, highlighting the importance of the CNC aggregation state. Overall, CNC-surfactant interactions enable tunable control over interfacial structure and foam stability, offering valuable insights for greener formulations in personal care, food, and household applications.