Mimicking coalescence using a pressure-controlled dynamic thin film balance

Area of Science:

• Physical Chemistry
• Materials Science
• Fluid Dynamics

Background:

• Thin films composed of polymer solutions are crucial in various industrial processes.
• Understanding their stability and coalescence dynamics is essential for process optimization.
• Previous studies often lack precise control over pressure dynamics during film evolution.

Purpose of the Study:

• To investigate the complex dynamics of thin polymer solution films under controlled pressure variations.
• To mimic and analyze the pressure evolution during bubble approach and separation.
• To identify key factors governing film stability, drainage, and coalescence.

Main Methods:

• Utilized a novel pressure-controlled thin film balance capable of precise pressure adjustments (magnitude, sign, duration).
• Mimicked bubble coalescence scenarios by controlling pressure drops across the film.
• Observed and analyzed film drainage, shape evolution, and stability under varying pressure conditions.

Main Results:

• Film dynamics, including drainage and shape, exhibited non-trivial dependence on applied pressure magnitude and duration.
• Negative pressure gradients revealed an interplay between capillarity and hydrodynamics, affecting film thickening and thinning.
• Distinct film break-up regimes were identified based on the dominance of capillary or hydrodynamic forces.

Conclusions:

• The study provides critical insights into thin film behavior during bubble separation.
• Optimal conditions for polymer solution film coalescence can be determined using this method.
• Findings facilitate the enhancement of population balance models for thin film phenomena.