What birds have taught us about structural colors School of Engineering and Applied Sciences Department of Physics, Harvard University Funding: International Collaboration grant (No.Sunjin-2010-002) from Korean Ministry of Knowledge Economy, Harvard MRSEC (NSF DMR-0820484) Sofia Magkiriadou, Jin-Gyu Park, Shin-Hyun Kim (KAIST), Young-Seok Kim (KETI), Gi-Ra Yi (SKKU), Adeline Perro, Guangnan Meng, Vinothan N. Manoharan
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What birds have taught us about structural colors
School of Engineering and Applied Sciences
Department of Physics,
Harvard University
Funding: International Collaboration grant (No.Sunjin-2010-002) from Korean Ministry of Knowledge Economy, Harvard MRSEC (NSF DMR-0820484)
Sofia Magkiriadou, Jin-Gyu Park, Shin-Hyun Kim (KAIST), Young-Seok Kim (KETI), Gi-Ra Yi (SKKU),
Adeline Perro, Guangnan Meng,
Vinothan N. Manoharan
Dramatis Personae
Sofia Magkiriadou Jin-Gyu Park
Young-Seok Kim (KETI)
Shin-Hyun Kim (KAIST)
Jason Forster (Yale)
Gi-Ra Yi (Sungkyunkwan U)
Eric Dufresne (Yale)
(collaborating with Mochrie and Prum)
Ordinary color and structural color
transmitted red and green
incident white light
scattered blue light
absorption of red and green
broadband adsorption
constructive interference of
scattered blue light
Physical models of structural color
Multilayer interference (Rayleigh, 1917)
l
Incident wave Scattered waves
Diffraction (Bragg & Bragg, 1913)
Bragg’s Law:
Bragg diffraction: a simple model for iridescence in porous structures
2 sinn dl
l
Incident wave Scattered waves
5 years ago: biomimetic structural color
Forster, Noh, Liew, Saranathan, Schreck, Yang, Park, Prum, Mochrie, O’Hern, Cao, Dufresne Advanced Materials 22: 2939 (2010). See also: García, Riccardo, and López. Advanced Materials (2010)
A C
0.5 μm 2 μm 18
cm
Dufresne (Yale)
Dried polystyrene microspheres (~250 nm)
Bragg’s Law:
In ordered materials, the color depends on viewing angle
2 sinn dl
~5°with respect to light source
~50°
1 μm 1 μm
l
Incident wave Scattered waves
In amorphous materials, the color is angle-independent
Same sample, tilted by ~ 60 degrees (SM).
226 nm polystyrene beads
3 m
m
Angle-independent color also comes from constructive interference
Short-range correlations between particles → Constructive interference
Rotational symmetry → Orientation independence
Str
uct
ure
fac
tor
S(q
)
q
θ Forster et al., Adv. Mater. 2010
correlations with wavevector
𝑞structure ≈ 2𝜋/𝑑
interparticle distance d
𝑞scat = 4𝜋/𝜆 sin 𝜃/2
𝑞scat = 𝑞structure at resonance
wavelength of structural color: 𝜆color ≈ 2𝑑
Consider reflected light: 𝜃 = 𝜋
An application: reflective color displays
w/ Young-Seok Kim (KETI) Gi-Ra Yi (SKKU) Shin-Hyun Kim (KAIST)
A proposal: make color “ink” particles for flexible, reflective color displays (Grant No.Sunjin-2010-002 from Korean Ministry of Knowledge Economy)
Requirements:
- wide viewing angle
- small particles (~10 micron)
- saturated color
Potential problems for display applications
Pictures from Forster et al., Adv. Mater. 2010
White color except in thin films (or with absorbing materials added)
Appearance (saturation, transparency) not easily controlled
How to make “ink” particles?
Analysis: length scales
scaQ
al
l
3
4
)( 1
cos
)1/(*
g
gll
Forster et al., Adv.Mater. 2010
Sample thickness L (or absorption length Labs)
Scattering length l distance over which
intensity decays
Transport length l* distance over which
propagation direction is randomized
L
g: asymmetry parameter g = 0 : isotropic g = 1 : forward scattering
Qsca: scattering efficiency
Design rule: minimize multiple scattering (maximize transport length) of non-resonant wavelengths
incident white light
scattered blue light
transmitted light
Design rules:
L, Labs < l* (no multiple scattering)
2d ~ λ (resonance condition)
Problem: transport length depends on particle size, which also determines color
20-200 nm
200 - 400 nm
Solution: make composite particles
(decouple interparticle spacing from particle size)
How to shift the resonances independently: photonic capsules of core-shell particles
L
Photonic capsules with microfluidics
S. H. Kim, J.-G. Park, T. M. Choi, V. N. Manoharan, and D. A. Weitz, Nature Communications 2014. J.G. Park, S.-H. Kim, S. Magkiriadou, T. M. Choi, Y.-S. Kim, V. N. Manoharan, Angewandte Chemie International Edition 2014