Photonic balls are spheres tens of micrometers in
diameter containing assemblies of nanoparticles or nanopores with a
spacing comparable to the wavelength of light. When these
nanoscale features are disordered, but still correlated, the photonic
balls can show structural color with low angle-dependence. Their
colors, combined with the ability to add them to a liquid
formulation, make photonic balls a promising new type of pigment
particle for paints, coatings, and other applications. However, it is
challenging to predict the color of materials made from photonic
balls because the sphere geometry and multiple scattering must be
accounted for. To address these challenges, we develop a multiscale
modeling approach involving Monte Carlo simulations of multiple
scattering at two different scales: we simulate multiple scattering and absorption within a photonic ball and then use the results to
simulate multiple scattering and absorption in a film of photonic balls. After validating against experimental spectra, we use the
model to show that films of photonic balls scatter light in fundamentally different ways than do homogeneous films of nanopores or
nanoparticles, because of their increased surface area and refraction at the interfaces of the balls. Both effects tend to sharply reduce
color saturation relative to a homogeneous nanostructured film. We show that saturated colors can be achieved by placing an
absorber directly in the photonic balls and mitigating surface roughness. With these design rules, we show that photonic-ball films
have an advantage over homogeneous nanostructured films: their colors are even less dependent on the angle.
more »
« less
Bidispersed Colloidal Assemblies Containing Xanthommatin Produce Angle‐Independent Photonic Structures
The biological chromophore xanthommatin (Xa) contributes to the yellow, red, and brown colors and hues in cephalopods and arthropods. In many cases, Xa is also present as part of or coupled to supramolecular nanostructures, whose function has yet to be fully explored. To investigate how such structural elements impact the perceived color of these natural chromophores, amorphous photonic assemblies containing Xa chemically coupled to 100 nm polystyrene nanoparticles (PS100‐XA) are fabricated, and blended with pure polystyrene (PS) nanoparticles of varying sizes. Structural colors are observed comprising these bidispersed colloidal assemblies that are tuned by the particle size of PS nanoparticles, the concentration of PS100‐XA, the local environment, and the method of assembly. In all cases, the addition of PS100‐XA regulates the color hue and contrast of the resultant assemblies by increasing light absorption while minimizing incoherent light scattering. Taken together, the results demonstrate how biochromes like Xa can enhance the color intensity and the diversity in colors present in common photonic assemblies.
more » « less- Award ID(s):
- 1945207
- NSF-PAR ID:
- 10448311
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 9
- Issue:
- 24
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract In this report the design, fabrication, and testing of inkjet‐printed electrochromic pixels (ECPs) incorporating the biochrome, xanthommatin (Xa) as programmable display units is described. As a redox sensitive chromophore, Xa is present in some species as a physiological indicator with red (reduced) or yellow (oxidized) colors associated with different behavioral or developmental stages. These features have been recently leveraged in some materials applications, illustrating a bio‐inspired design solution to color‐changing sensors and displays. This paper describes an extension of these applications to print individually addressable ECPs that can be processed in a mild annealing step to introduce localized conductivity on initially nonconductive substrates. When formulated together with a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) carrier ink, an addition of 0.19 wt% Xa is enough to generate dynamic ECPs which can be batch printed as lateral electrodes on any substrate to serve as both conductors and display units across electrically isolated boundaries. Application of low potentials triggers reversible color changes that span the red/yellow color space and can cycle for days. These results represent an important step towards the incorporation of alternative active materials like Xa to manufacture and scale low‐power, color‐changing pixels and patterns.
-
Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.more » « less
-
more » « less
Abstract Nanostructured materials have enabled new ways of controlling the light–matter interaction, opening new routes for exciting applications, in display technologies and colorimetric sensing, among others. In particular, metallic nanoparticles permit the production of color structures out of colorless materials. These plasmonic structural colors are sensitive to the environment and thus offer an interesting platform for sensing. Here, a self‐assembly of aluminum nanoparticles in close proximity of a mirror is spaced by an ultrathin poly(
N ‐isopropylacrylamide) (PNIPAM) layer. Hybridizing the plasmonic system with the active polymer layer, a thermoresponsive gap‐plasmon architecture is formed that transduces changes in the temperature and relative humidity of the environment into color changes. By harnessing the environmentally induced structural changes of PNIPAM, it was estimated from the finite difference time domain simulation that the resonance can be tuned 7 nm per every 1 nm change in thickness, resulting in color variation. Importantly, these fully reversible changes can be used for reusable powerless humidity and temperature colorimetric sensing. Crucially if condensation on the structure happens, the polymer layer is deformed beyond recovery and the colors are washed away. We leverage this effect to produce tamper‐proof dew labels that a straightforward smartphone app can read by taking a picture. -
more » « less
Abstract A mechanochromic, programmable, cholesteric liquid crystalline elastomer (CLCE) is fabricated, and after straining, resulting in a blue shift through the visible spectrum, is returned to its initial shape and color upon heating through its isotropic phase transition. Light initiated, radical‐mediated, addition fragmentation chain transfer (AFT), facilitate permanent programming or erasure of thermoreversible shape and color by relaxing stress imparted on the strained network through reversible bond exchange. Thermoreversible strain is coupled with reversible color change and can be made permanent at any desired strain by light exposure and corresponding AFT activation, temporarily restoring nearly initial shape and color upon heating. The optical characteristics and photonic structure, inherently linked to the network, are measured as a function of strain, to confirm the reflection notch narrowing indicating that prepolymerization alignment via shearing is poor thereby causing a broad spectrum of reflected light that narrows when the material is stretched. Beyond programming a new shape and color, the reflection notch is erased and separately, photopatterned to achieve dynamic color schemes that are toggled with heating and cooling, similar to that of a chameleon's camouflaging technique that has the ability to manipulate multiple colors in a single material, also with use for strain mapping.
