Evaporation-induced Rayleigh-Taylor instabilities in polymer solutions

Area of Science:

• Fluid dynamics
• Polymer science
• Materials science

Background:

• Solvent evaporation in polymer solutions can induce convective instabilities.
• Known mechanisms include Rayleigh-Bénard and Marangoni instabilities.
• A new mechanism involving Rayleigh-Taylor instabilities due to interfacial layer formation is proposed.

Purpose of the Study:

• To investigate the onset time of Rayleigh-Taylor instabilities in drying polymer solutions.
• To understand the influence of polymer concentration, molecular weight, and diffusivity on instability dynamics.
• To elucidate the role of interfacial tension and viscosity in stabilizing these systems.

Main Methods:

• Experimental study of aqueous polymer solutions.
• Systematic variation of polymer concentration (c0), molecular weight, and type.
• Measurement of instability onset time (t) as a function of macroscopic properties.

Main Results:

• In dilute solutions, onset time depends on polymer diffusivity.
• High diffusivity polymers show t scaling with diffusion.
• Low diffusivity polymers exhibit concentration-dependent scaling due to interfacial tension effects.
• Above a critical concentration, viscosity influences stabilization, leading to t scaling as (ν/c0)2/3.

Conclusions:

• Evaporation-induced Rayleigh-Taylor instabilities are identified in polymer solutions.
• Polymer diffusivity and concentration are key factors governing instability onset.
• Interfacial tension and viscosity play critical roles in stabilizing the drying interface, with implications for film coating processes.