Unusual Contact-Line Dynamics of Thick Films and Drops

Area of Science:

• Fluid dynamics
• Surface science
• Physics of interfaces

Background:

• Understanding fluid behavior at macroscopic scales is crucial for various applications.
• Contact-line dynamics and fingering instabilities are complex phenomena influenced by multiple forces.

Purpose of the Study:

• To investigate novel phenomena in contact-line and fingering dynamics of macroscopic spinning drops and gravity-driven films.
• To analyze the influence of external body forces, capillarity, viscosity, and intermolecular forces on fluid behavior.
• To explore the mechanisms behind finger development and spreading dynamics.

Main Methods:

• Experimental analysis of macroscopic spinning drops and gravity-driven films.
• Theoretical analysis of interfacial shapes and dynamics.
• Investigation of fluid properties like viscosity and wetting behavior.

Main Results:

• Macroscopic films exhibit multi-valued interfacial shapes near the contact line due to force balances.
• A single finger develops on partially wetting spinning drops via a distinct mechanism.
• Glycerine finger speed increases with viscosity at high viscosity and low rotation frequencies.
• Completely wetting fluids spread faster on dry surfaces than prewetted ones.
• Prewetted films suppress fingering in gravity-driven flow and spin coating.

Conclusions:

• Macroscopic fluid interfaces display rich and unexpected dynamics governed by a interplay of forces.
• The study reveals unique fingering mechanisms and spreading behaviors not observed in microscopic systems.
• Findings offer insights into fluid behavior relevant to coating, printing, and other industrial processes.