In situ monitoring of structural changes during colloidal self-assembly

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Colloidal systems self-assemble into ordered structures, forming photonic crystals.
• Understanding structural evolution during self-assembly is crucial for material design.
• Solvent evaporation at a sessile drop meniscus drives heterogeneous crystallization.

Purpose of the Study:

• To monitor structural changes during colloidal self-assembly using reflectance spectroscopy.
• To analyze the self-assembly process by treating the colloidal structure as a photonic crystal.
• To investigate the mechanism behind cracking in colloidal crystals.

Main Methods:

• Utilizing reflectance spectroscopy to track structural evolution.
• Applying a modified Bragg's law model for photonic crystals.
• Observing self-assembly in a sessile drop under ambient conditions.

Main Results:

• A face-centered cubic (FCC) structure formed after an induction period.
• The FCC lattice parameter initially decreased with increasing colloidal concentration due to drying.
• An abrupt lattice shrinkage occurred, resembling martensitic transformations, correlating with Debye screening length.

Conclusions:

• Reflectance spectroscopy effectively monitors colloidal self-assembly and structural changes.
• The observed lattice shrinkage mechanism provides insight into colloidal crystal formation.
• The final lattice shrinkage is a potential cause for cracking in colloidal crystals.