Sub-Newtonian coalescence in polymeric fluids.

Area of Science:

• Fluid Dynamics
• Polymer Physics
• Rheology

Background:

• Droplet coalescence is crucial in various industrial processes.
• Understanding coalescence in complex fluids like polymers requires advanced models.

Purpose of the Study:

• To develop a theoretical framework for pendant and sessile drop coalescence in polymeric fluids.
• To identify new flow regimes and parameters governing this phenomenon.

Main Methods:

• Unification of constitutive laws under a high Weissenberg creeping flow limit.
• Development of a new timescale integrating elastocapillary number and entanglement density.
• Validation using high-speed imaging experiments with poly(ethylene oxide) (PEO).

Main Results:

• Identification of a sub-Newtonian regime and arrested coalescence.
• Characterization of the arrest angle (θ_arrest) dependence on the inverse Elasto-capillary number (Ec⁻¹).
• Proposal of a new timescale (T*) for liquid neck evolution.

Conclusions:

• The proposed framework accurately captures droplet coalescence in polymeric fluids.
• The study introduces a novel understanding of flow regimes and timescales in polymer fluid dynamics.
• Experimental validation confirms the theoretical predictions across varying polymer molecular weights.