Nano-mechanical properties of clay-armoured emulsion droplets

There has been a growing interest in understanding the stabilization mechanism of particle-armoured emulsion droplets over the last few decades due to their importance in many everyday products. Here, the mechanical properties of clay-armoured emulsion droplets were investigated using laser scanning confocal microscopy with an in situ atomic force microscopy measurement. This combination allows the visualization of droplet shape as a function of applied force. The emulsion droplets were found to be mechanically robust, stable against coalescence during drop collisions and able to recover from large deformations without disintegration. A Hookean constitutive law was used to extract the surface Young's modulus of the clay-armoured droplets as a function of a range of solution conditions. The clay-armoured droplets were relatively insensitive to changes in solution ionic strength and pH. However, in the presence of cationic surfactants, the surface Young's modulus decreases and shows significant reduction well above the critical micelle concentration. These changes are most likely due to desorption of clay platelets from the oil-water interface after charge neutralisation and the eventual solubilisation of the oil droplet. The elasticity measurements in this study should help illuminate the impact of the clay-armoured droplets on macroscopic properties of emulsions including rheological properties and emulsion stability.