Mono-emulsion droplet stretching under direct current electric field

Area of Science:

• Fluid Dynamics
• Electrokinetics
• Colloid Science

Background:

• Understanding droplet behavior in electric fields is crucial for microfluidics and materials science.
• Mono-emulsion droplet deformation and breakup are complex phenomena influenced by various physical parameters.

Purpose of the Study:

• To investigate the mechanism of stretching and breaking of mono-emulsion droplets under a direct current electric field.
• To develop a theoretical model for the transition from equilibrium deformation to non-equilibrium breaking.
• To determine the critical electric capillary number ((Cae)crit) and its dependence on conductivity and viscosity ratios.

Main Methods:

• Theoretical analysis
• Experimental approaches
• Numerical simulations
• Axisymmetric straining flow analysis

Main Results:

• Droplet deformation occurs along the electric field direction below a critical electric capillary number ((Cae)crit).
• At (Cae)crit, droplets break rapidly, with daughter droplet ejection driven by concentrated electric stresses.
• The theoretical model predicts (Cae)crit ≈ 0.25 for a conductivity ratio (R) of approximately 10, aligning with experimental results of (Cae)crit ≈ 0.245.
• (Cae)crit decreases as R increases, while the viscosity ratio affects breakup modes but not (Cae)crit.

Conclusions:

• The study elucidates the mechanism of electric field-induced droplet deformation and breaking.
• A critical electric capillary number governs the transition from stable deformation to rapid breakup.
• Conductivity ratio significantly influences (Cae)crit, whereas viscosity ratio does not impact the onset of breaking.