Exploring colloidal particle behavior at the water-water interface: a new method for measuring the interfacial tension

Aqueous two-phase systems (ATPS), formed from immiscible polymer-polymer or polymer-salt solutions in water, have gained attention for their biocompatibility and eco-friendly properties, making them suitable for applications in biomedical engineering and green chemistry. To enhance their effectiveness, maximizing the internal interfacial area is critical, leading to recent advancements in emulsion-based ATPS. However, stabilizing the water-water interface with colloidal particles remains a significant challenge. This study investigates colloidal particle behavior at the water-water interface, analyzing their aggregation, growth into larger structures, and detachment from the interface over time at varying concentrations. By quantifying key interaction forces, including depletion, capillary, van der Waals, and electric double-layer forces, we identify dominant forces at each stage. Using image processing to assess aggregate sizes before detachment, we develop a novel method for measuring interfacial tension. This versatile approach accommodates diverse particle sizes and densities, offering insights into the mechanisms governing particle behavior at water-water interfaces.