posted on 2021-12-01, 17:04authored byLaurinda
R. P. Areias, Gema Marcelo, José Paulo S. Farinha
While the color of conventional pigments
and dyes is related to
the absorption of light, structural color results from selective light
scattering by nanostructures with an appropriate periodic variation
of refractive index. The latter can be obtained from virtually any
material and produce a coloration that appears considerably brighter
and is more resistant to fading. We developed colloidal photonic pigments
with spherical symmetry from polymer nanoparticles (PNP) of styrene
and acrylate monomers, using their surface charge to control the self-assembly
by droplet microfluidic emulsification. By changing only the size
of the PNPs, we are able to produce colors across the entire visible
spectra. Unlike most other spherical photonic pigments, our materials
present bright saturated colors and virtually no iridescence. We achieved
this by doping the pigments with polydopamine (PD) nanoparticles.
The latter can both reduce the long-range order in the photonic pigments
and absorb the diffuse light scattering from structural defects, as
shown by electronic microscopy and reflective confocal microscopy
(RCM). Nanostructured PD-doped spherical photonic pigments can be
obtained from sustainable materials and hold enormous potential for
technological applications from dye-free color coatings to stimuli-responsive
coloring, dye-free colorimetric sensors, and reflective color screens.