Impact of molecular composition and sequential aqueous-phase exchange on polyglycerol polyricinoleate interfacial...

The functional efficiency of polyglycerol polyricinoleate at oil-water interfaces depends not only on its intrinsic surface activity but also on the adaptive behavior of pre-adsorbed films when the surrounding aqueous environment changes. Specifically, variations in PGPR molecular composition may influence interfacial adsorption behavior and interfacial organization, while aqueous-phase perturbations modulate the viscoelastic response of these pre-adsorbed films.

Four commercial PGPRs with distinct molecular compositions were first characterized under static conditions using drop shape tensiometry to compare interfacial tension, adsorption kinetics, and dilatational viscoelastic properties. The PGPR with the lowest interfacial tension was selected for subsequent dynamic studies. A drop shape tensiometer with peristaltic pump-enabled aqueous phase exchange was used to expose pre-adsorbed PGPR films to proteins of different types and concentrations as well as different NaCl concentrations, with real-time interfacial tension monitoring during exposure and dilatational rheological measurements after re-equilibration.

Static characterization revealed that larger polyglycerol headgroups promoted faster apparent diffusion and reduced interfacial tension, while polyricinoleate tail variations influenced penetration dynamics. Despite these differences, all PGPRs films with comparable viscoelastic modulus at equilibrium. In dynamic experiments, proteins and NaCl modulated the interfacial tension and viscoelasticity of pre-adsorbed PGPR films in a concentration- and identity-dependent manner. The results suggest that aqueous-phase perturbations can induce adaptive interfacial reorganization and reinforce the viscoelastic properties of PGPR-stabilized films while preserving their characteristic rheological behavior. Collectively, these findings provide new insights into structure-function relationships and environmental responsiveness, advancing the fundamental understanding of surfactant films stability in complex W/O systems.