Active compound particles in a quadratic flow: hydrodynamics and morphology.

Area of Science:

• Fluid dynamics
• Soft matter physics
• Microfluidics

Background:

• Controlling core-shell particle morphology is crucial for tuning their properties.
• Microfluidic devices often utilize quadratic flow for particle generation.
• Active compound particles, consisting of an active particle within a fluid droplet, are of interest.

Purpose of the Study:

• To investigate the hydrodynamics and morphology of concentric active compound particles in quadratic flow.
• To understand the interplay between flow characteristics and particle activity on particle shape.

Main Methods:

• Analytical solutions to governing fluid flow equations in the inertia-less limit (low capillary number, Ca ≪ 1).
• Analysis of deformation under imposed quadratic (Poiseuille) flow and internal activity (force dipole).

Main Results:

• Quadratic flow deforms the particle into a three-lobe structure, influenced by the hexapolar flow component.
• Particle activity induces prolate deformation due to the force dipole velocity field.
• Activity breaks the three-lobe symmetry, leading to asymmetric and elongated shapes.
• Particle breakup susceptibility increases with stronger activity, specific orientations, small size ratios, and low viscosity ratios.

Conclusions:

• Particle morphology is highly sensitive to the relative strengths and orientations of activity and quadratic flow.
• Pulsatile quadratic flow can prevent active compound particle breakup during generation and transport.
• Pulsatile flow offers a method for actively tuning the morphology of these particles.