Shape Deformation of Liquid Droplets Falling in a Liquid Media

We experimentally investigate the dynamics of aqueous droplets falling through a stationary oleic micellar solution under gravity. Our study focuses on understanding the influence of droplet size, interfacial tension, nanoparticle concentration in droplet, and surfactant concentration in the continuous phase on droplet deformation. Side view images of the falling process reveal that the DI-water drop undergoes a sinusoidal deformation cycle from a sphere shape to oval and ultimately pancake shape. However, the addition of nanoparticles in the aqueous drop leads to a greater droplet deformation but reduced oscillation. Ultimately, at the nanoparticle concentrations above 4 wt.%, the oscillations decay over time where the droplets keep their flattened pancake shape. While the ultra-low interfacial tension contributes in the pancake drop shape, it is hypothesized that the formation of a viscoelastic interfacial layer, made of emulsions, at the drop interface attenuates the drop oscillation. These findings have potential applications in various fields including microfluidics, emulsion formation, and industrial processes involving liquid-liquid interactions.