Stable and unstable surface evolution during the drying of a polymer solution drop.

Area of Science:

• Materials Science
• Fluid Dynamics
• Polymer Science

Background:

• Sessile drops of complex liquids exhibit shape changes during drying.
• Pure hydrosoluble polymers can form a glassy solid state.

Purpose of the Study:

• Investigate the buckling instability during the drying of a glassy polymer sessile drop.
• Understand the conditions leading to shape distortion and secondary instabilities.

Main Methods:

• Utilized a model system of a hydrosoluble polymer.
• Studied solvent evaporation and polymer accumulation at the vapor/drop interface.
• Developed a model comparing drying and glassy skin formation timescales.

Main Results:

• Observed the formation of a bending glassy skin due to polymer accumulation.
• Identified conditions for buckling instability, well-explained by the model.
• Documented various shape distortions and axisymmetry-breaking secondary instabilities.

Conclusions:

• Drying-induced glassy skin formation drives buckling instability in sessile polymer drops.
• The interplay between drying rate and skin formation dictates instability occurrence.
• Experimental conditions control the type and complexity of observed shape distortions.