Numerical simulation and analysis of droplet formation within an amphiphilic particle

An instrument-free particle-templated droplet formation can be achieved upon simple mixing of amphiphilic particles with aqueous and oil phases in a well plate by using a common lab pipette. Here, a two-dimensional, two-phase flow model was established using a finite element method to mimic the droplet formation within a concentric amphiphilic particle, which consisted of an outer hydrophobic layer and an inner hydrophilic layer. Immiscible water and oil phases selectively interacted with the hydrophilic and hydrophobic layers of the particle, respectively, to form an isolated aqueous compartment within a cavity. Three extreme models were also simulated, including completely hydrophilic, completely hydrophobic, and oppositely amphiphilic particle, which indicated that a right order of the particle layers was necessary to capture the droplet inside the cavity. Moreover, we performed a systematic study of particle-templated droplet formation by varying the individual layer thicknesses of particle, particle height, interfacial tension between water and oil, contact angle of interface with different surfaces, velocity of incoming oil media, and distance between neighboring particles. The volume fraction of water droplet trapped within the target cavity region was calculated to characterize the droplet formation. Our work will help to optimize the particle fabrication process, predict the experiment droplet formation, and explain the physical mechanism underlying compartmentalization phenomena.