Measuring interactions between Pickering emulsion droplets coated with casein–chitosan complex using optical tweezers

Emulsions stabilized by protein/polysaccharide complexes have attracted great interest. However, the emulsion properties and interactions between droplets at the microscale require further investigation. In this work, the interaction forces between two rice bran oil droplets stabilized by casein-chitosan complexes, with a diameter of 3 ± 0.1 μm (pH 5.54 and no-salt), were measured under different aqueous conditions (pH and ionic strength) using optical tweezers. The measured force curves exhibited consistency with the interfacial layer conformation and interfacial charge, as determined through fluorescence spectroscopy and zeta-potential analysis. Furthermore, atomic force microscopy (AFM) and optical microscopy were employed to characterize the morphology and structural evolution of the emulsions under varying environmental conditions. Our results provide a useful method for studying the interaction forces between Pickering emulsion droplets with pN force resolution and reveal the correlation between interfacial layer properties and physical stability, offering deep insights into the stabilization mechanism of Pickering emulsions.