Mechanistic study of droplets coalescence in Pickering emulsions

Abstract

Dissipative particle dynamics (DPD) simulations were performed to study the stability of Pickering emulsions. Two droplets covered by nanoparticles were forced to coalesce. The simulated experiment was systematically repeated for a number of conditions. Decane droplets in water as well as water droplets in decane were considered. The density of the nanoparticles on the droplets surface was varied. Homogeneous and Janus nanoparticles with contact angles ranging from ∼40° to ∼130° were considered. The maximum force experienced by the droplet during collision was recorded to qualitatively discriminate the ability of the nanoparticles to stabilize Pickering emulsions. The nanoparticles density on the droplets surface is found to be the most important parameter. When the density is large enough, the three-phase contact angle discriminates between nanoparticles that are effective at stabilizing emulsions and those that are not. At comparable coverage and contact angles, Janus nanoparticles can be more effective than homogeneous nanoparticles. By examining the simulation snapshots, the stabilization mechanism is discussed. Our analysis confirms that the steric interactions between nanoparticles adsorbed onto the coalescing droplets, the ability of the nanoparticles to adsorb simultaneously on two interfaces, and the stability of the film formed in between the coalescing droplets are all important phenomena that can be employed to stabilize Pickering emulsions.