Observation of solid-solid transitions in 3D crystals of colloidal superballs

Area of Science:

• Materials Science
• Soft Matter Physics
• Crystallography

Background:

• Anisotropic colloidal suspensions self-organize into diverse crystal and liquid crystal phases driven solely by particle shape.
• Simulations predict phase behavior for various shapes, but experimental validation often lags.
• Superball particles, with shapes intermediate between spheres and cubes, offer a unique system for studying shape-induced self-assembly.

Purpose of the Study:

• To experimentally investigate the phase behavior of superball particles.
• To compare experimental findings with theoretical predictions for anisotropic particle self-assembly.
• To explore the potential for controlling self-assembly of superballs into functional materials.

Main Methods:

• Synthesis and characterization of superball particles.
• Experimental observation of phase transitions using techniques like microscopy and scattering.
• Analysis of crystal structures and stacking variants.

Main Results:

• Observation of a plastic crystal phase with translational order but orientational disorder.
• Formation of rhombohedral crystals from the plastic crystal phase.
• Discovery of two distinct rhombohedral crystal structures with different stacking (hollow-site and bridge-site).
• Identification of a solid-solid transition between the two rhombohedral phases for softer interactions.

Conclusions:

• The experimental phase behavior of superballs is more complex than predicted by simulations.
• Superball particles exhibit unique self-assembly pathways leading to novel crystalline structures.
• This research contributes to understanding and controlling the self-assembly of anisotropic particles for applications like photonic crystals.