Microstructures by solvent drop evaporation on polymer surfaces: dependence on molar mass

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Solvent drop evaporation on polymer surfaces typically forms craters.
• Understanding the influence of polymer properties on drying patterns is crucial for materials fabrication.

Purpose of the Study:

• To investigate the effect of polystyrene (PS) molar mass on surface structures formed after toluene solvent drop evaporation.
• To correlate observed surface topographies with polymer entanglement and drying dynamics.

Main Methods:

• Deposition of toluene drops onto planar polystyrene surfaces using a microsyringe.
• Analysis of surface topography after solvent drying using advanced imaging techniques.

Main Results:

• Low molar mass PS (20.9-24.3 kDa) formed dotlike protrusions with peripheral ridges.
• Increasing molar mass led to central height reduction, forming crater-like structures (29.6-643 kDa) with central depressions and ridges.
• Very high molar mass PS resulted in irregular, non-rotational symmetric structures.

Conclusions:

• Polystyrene molar mass significantly dictates the morphology of dried solvent drops.
• Molecular entanglement influences dissolution rates and diffusion constants, thereby controlling the final surface structure.
• The study provides insights into controlling surface patterns through polymer selection during solvent-assisted fabrication.