Direct observation of size fractionation during colloidal crystallization

Area of Science:

• Colloid science
• Materials science
• Crystallization dynamics

Background:

• Binary mixtures of colloids are used in advanced materials.
• Understanding crystallization in these systems is crucial for material design.
• Previous theoretical work suggested size segregation during crystallization.

Purpose of the Study:

• To experimentally investigate the crystallization of a binary mixture of spherical colloids.
• To provide real-space evidence for size segregation during colloidal crystallization.
• To analyze the crystalline structure and inter-species interactions.

Main Methods:

• Confocal microscopy was employed to study quasi-two-dimensional crystallization.
• Experiments utilized binary mixtures of spherical colloids coated with DNA strands.
• Lattice spacings of the resulting colloidal crystals were analyzed.

Main Results:

• Complete demixing of the two colloidal species was observed in the crystalline phase.
• A 10% difference in diameter between the two colloid species was determined.
• The observed demixing was attributed to size segregation during the crystallization process.

Conclusions:

• This study provides the first real-space experimental confirmation of size segregation in binary colloidal crystallization.
• The findings support theoretical predictions regarding size-driven demixing.
• The results have implications for designing and controlling the structure of colloidal materials.