Control of the Colloidal and Adsorption Behaviors of Chitin Nanocrystals and an Oppositely Charged Surfactant at Solid, Liquid, and Gas Interfaces.

Chitin has a unique hierarchical structure, spanning the macro- and nanoscales, and presents chemical characteristics that make it a suitable component of multiphase systems. Herein, we elucidate the colloidal interactions between partially deacetylated chitin nanocrystals (cationic ChNC) and an anionic surfactant, sodium dodecyl sulfate (SDS). We investigate charge neutralization and association (electrophoretic mobility, surface tensiometry, and quartz crystal microgravimetry) and their role in the stabilization of Pickering emulsions. We find SDS adsorption and association with ChNC under distinctive regimes: At low SDS concentration, submonolayer assemblies form on ChNC, driven by the hydrophobic effect and electrostatic interactions. With the increased SDS concentration, bilayers or patchy bilayers form, followed by adsorbed hemimicelles and micelles. We further suggested the role of hydrophobic effects in the observed colloidal transitions and complex conformations. At the highest SDS concentration tested, charge neutralization and SDS/ChNC flocculation take place. Remarkably, at given concentrations, adsorbed SDS endows the chitin nanoparticles with an effective hydrophobicity that opens the opportunity to achieve tailorable Pickering stabilization. Hence, a facile route is proposed by in situ modification by SDS physisorption, which extends the potential of renewable nanoparticles in the formulation of complex fluids, for instance, those relevant to household and healthcare products.