posted on 2021-05-14, 11:04authored byYoung
Geon Kim, Sanghyuk Park, Ye Hun Choi, Sang Hoon Han, Shin-Hyun Kim
Colloidal
crystals develop structural colors through wavelength-selective
diffraction. Recently, a granular format of colloidal crystals has
emerged as building blocks to construct macroscopic photonic surfaces
or architectures with high reconfigurability through the secondary
assembly. Here, we design elastic photonic microcapsules containing
colloidal crystallites along the inner wall as a building block. Water-in-oil-in-water
double-emulsion templates are microfluidically prepared to have an
aqueous dispersion of polystyrene particles in the inner droplet and
polydimethylsiloxane prepolymers in the shell. Colloidal particles
are enriched in the presence of depletant and salt by osmotic compression,
with the crystallization at the inner interface by depletion attraction.
The number of nucleation sites depends on the rate of the enrichment,
which enables control over the size and surface coverage of the crystallites
with osmotic conditions. The enrichment is ceased by transferring
the droplets into an isotonic solution, and the oil shell is cured
to form an elastic membrane. As the elastic microcapsules have a large
void in the core, they are deformable without structural damage in
the crystallites. Therefore, the microcapsules can be closely packed
to form macroscopic surfaces while achieving a high quality of structural
colors with a collection of crystallites aligned along the flattened
membrane.