Photonic Microcapsules Containing Single-Crystal Colloidal Arrays with Optical Anisotropy

Area of Science:

• Materials Science
• Soft Matter Physics
• Nanotechnology

Background:

• Colloidal particles with repulsive interactions self-assemble into crystalline lattices.
• These colloidal crystals are valuable for photonic material applications.
• Predicting and controlling crystal structures within spherical geometries is challenging.

Purpose of the Study:

• To experimentally determine the optimal arrangement of charged colloids within spherical microcapsules.
• To investigate the influence of interparticle repulsion strength on colloidal crystal formation.
• To understand the kinetic and thermodynamic factors governing crystal structure in confined spherical volumes.

Main Methods:

• Encapsulation of charged colloidal particles within double-emulsion drops.
• Controlled variation of interparticle repulsion strength.
• Microscopic observation of colloidal crystal growth dynamics and final structures.

Main Results:

• Strong interparticle repulsion promotes rapid, surface-initiated growth forming onion-like colloidal crystals.
• Weak repulsion allows for slower growth and rearrangement into thermodynamically favorable single-crystal phases.
• A kinetic barrier prevents rearrangement from the onion-like structure to the single-crystal phase, even when energetically favorable.

Conclusions:

• The interplay between kinetics and thermodynamics dictates colloidal crystal structure in spherical confinement.
• Onion-like and single-crystal structures exhibit distinct anisotropic optical properties, dependent on orientation.
• This work provides insights into designing colloidal photonic materials with tunable optical responses.