Soft gliadin nanoparticles at air/water interfaces: The transition from a particle-laden layer to a thick protein film

Hypothesis Protein-based soft particles possess a unique interfacial deformation behavior, which is difficult to capture and characterize. This complicates the analysis of their interfacial properties. Here, we aim to establish how the particle deformation affects their interfacial structural and mechanical properties. Experiments Gliadin nanoparticles (GNPs) were selected as a model particle. We studied their adsorption behavior, the time-evolution of their morphology, and rheological behavior at the air/water interface by combining dilatational rheology and microstructure imaging. The rheology results were analyzed using Lissajous plots and quantified using the recently developed general stress decomposition (GSD) method. Finding Three distinct stages were revealed in the adsorption and rearrangement process. First, spherical GNPs (∼105 nm) adsorbed to the interface. Then, these gradually deformed along the interface direction to a flattened shape, and formed a firm viscoelastic 2D solid film. Finally, further stretching and merging of GNPs at the interface resulted in rearrangement of their internal structure to form a thick film with lower stiffness than the initial film. These results demonstrate that the structure of GNPs confined at the interface is controlled by their deformability, and the latter can be used to tune the properties of prolamin particle-based multiphase systems.