Capillary Induced Motion of Particles in Thin Liquid Films

by Prof. Mahesh Tirumkudulu (IIT-Bombay)

Tuesday 15 Sept 2020, 15:00 → 16:30 Europe/Stockholm

Nordita

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https://stockholmuniversity.zoom.us/j/622224375

Meeting ID: 622 224 375
 

 Abstract: It has been long known that colloidal particles adsorb at a liquid-liquid or liquid-gas interface and play an important role in stabilizing emulsions and foams. More recently, there has been interest in assembling particles of varying shapes, sizes, and surface properties at interfaces in order to synthesize new materials. While most studies have investigated the role of capillary forces on particles at single interfaces, few have investigated the behavior of particles in thin films, where the particle size is comparable to the film thickness and may adsorb simultaneously at both interfaces. Such cases are especially important in understanding the role of particles in stabilizing foams and emulsions.

In the talk, we will present results for a new form of capillary force experienced by neutrally buoyant spherical particles adsorbed simultaneously at both interfaces of a thin liquid film of spatially varying thickness. The force is proportional to the slope of the interface and the difference between the local contact angle and the equilibrium value, and exists even when the two bounding interfaces have zero curvature. We derive the expression for the force, which when balanced against the hydrodynamic drag gives the trajectory of the particle. The measured trajectories for spherical particles of varying diameters in thin films compare well with predictions. The results highlight the importance of accounting for variable thickness in films stabilized by particles and explain some of the long-standing observations on foam stabilisation by particles.