Dynamics and stability of a compound particle -- a theoretical study

TL;DR

This theoretical study analyzes the dynamics and stability of concentric compound particles under external forces and flows, providing insights into their configuration, deformation, and methods for stable transportation in various applications.

Contribution

It offers analytical solutions for the flow fields and stability conditions of compound particles, including the effects of external forces and flows, which is novel in the context of soft matter physics.

Findings

Concentric configuration is a stable steady state under rotation.

Additional force is needed to stabilize translating compound particles.

Pulsatile flow can transport particles without causing breakup.

Abstract

Particles confined in droplets are called compound particles. They are encountered in various biological and soft matter systems. Hydrodynamics can play a decisive role in determining the configuration and stability of these multiphase structures during their preparation and use. Therefore, we investigate the dynamics and stability of a concentric compound particle under external forces and imposed flows. Governing equations are solved analytically in the inertia-less limit using the standard technique of superposition of vector harmonics and the solutions obtained are reported in terms of steady state flow fields, viscous drag on the particle and the time evolution of the confining drop shape. The limiting form of compound particle as a thin film coated rigid particle is analyzed in each case. We find that concentric configuration of a rotating compound particle is a steady state solution, and we calculate the extra force required to stabilize the concentric configuration of a translating compound particle. A comprehensive comparison of drop deformations in various linear ambient flows is also provided. Based on the findings, we propose pulsatile flow as a reliable method to transport compound particles without breakup of the confining drop. Thus, our analysis provides useful guidelines in preparation and transportation of stable compound particles in the context of nucleated cells, aerosols, droplet-based encapsulation of motile organisms and polymer microcapsules.