Supporting Information
Large-area crack-free single-crystal photonic crystals via combined
effect of polymerization-assisted assembly and flexible substrate
Jinming Zhou,1 Jingxia Wang,*1 Yu Huang,1,2 Guoming Liu,1 Libin Wang,1,2 Shuoran
Chen, 1,2 Xiuhong Li,3 Dujin Wang,1 Yanlin Song*1 and Lei Jiang1
1
Beijing National Laboratory for Molecular Sciences (BNLMS), Laboratory of New
Materials, Key Laboratory of Organic Solids, Laboratory of Advanced Polymer
Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R.
China
2
Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Zhangheng
Rd 239, Pudong Dist., Shanghai 201204, China
Correspondence: Dr. J. X. Wang or Prof. Y. L. Song, Laboratory of New Materials,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
E-mail: ylsong@iccas.ac.cn or wangzhang@iccas.ac.cn
Experimental.
Cu foils with thicknesses of 20, 50, 106, 175, 300 and 450 µm, Ti foils with
thicknesses of 35, 56, 105, 197, 309 and 424 µm, and Ni foils with thicknesses of 55 and
115 µm were purchased from Kaihua Aluminum Co., Ltd. Jiangsu, China. These foils
were ultrasonically cleaned in 1:1 absolute ethanol and acetone before use. Crotonyl
alcohol, trans-2-Butenoic acid, 2-hydroxyethyl methacrylate, 2-(Dimethylamino)ethyl
methacrylate were purchased from Sigma-Aldrich. Acrylic acid and acrylamide were
purchased from China Guoyao Chemical Co., Ltd. All reagents were purified prior to use.
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Figure S1. Optical microscope images of PNIPAm/Poly(St-MMA-AA) composite PCs
assembled on (a) 20-μm-thick Al foil and (b) on glass.
Clearly, the crack is eliminated when the PNIPAm/colloid composite PC is assembled
on Al foil, but numerous cracks occur on the sample obtained on the glass substrate.
Figure S2. (a-c) SEM images of the large area crack-free PCs assembled from
colliodal particles with diameters of (a)180, (b) 230 and (c) 260 nm (scale bar: 10 μm).
(d) UV-Vis spectra of the colloidal PCs assembled from different latex spheres, the
inserted numbers are the diameters of the colloidal spheres (nm).
2
Single-crystal characterization of crack-free PCs.
Figure S3. (a) Grazing incident small-angle X-ray diffraction pattern of as-prepared
crack-free composite PCs. (b) The simulated pattern of
-
-
<011> zone. Inserted in (a) is
the model of <011> zone. The as-prepared samples showed perfect single-crystalline
structure.
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Effect of monomers on the as-prepared composite PCs
Figure S4. SEM images of composite opal PCs co-assembled with aqueous monomers
of (a) acrylic acid, (b) acrylamide, (c) crotonyl alcohol, (d) trans-2-butenioc acid, (e)
2-hydroxyethyl methacrylate and (f) 2-(dimethyamino)ethyl methacrylate. The scale
bar is 20 μm (the inset scale bar is 1 μm).
Crack-free PCs could be obtained when the latex spheres were co-assembled using
aqueous monomers, such as acrylic acid, acrylamide, crotonyl alcohol and
2-hydroxyethyl methacrylate. But commonly PNIPAm/colloid PCs show the best
periodic structure.
Stopband positions with varying NIPAm/colloid ratios.
Figure S5. Reflectance spectra (a) and stopband positions (b) of PNIPAmpoly(St-MMA-AA) composite opal PCs at varying NIPAm/colloid weight ratios from 0:1,
0.5:1, 1:1, 1.5:1 to 2:1.
An obvious stopband red shift is observed for PNIPAm-colloid composite PCs when
monomer/colloid ratios are below 1:1, while the stopband red-shift becomes
inconspicuous when monomer/colloid ratios are above 1:1.
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Determination of the amount of infiltrated co-monomers.
Figure S6. Schematic illustration of shrinkage of colloidal spheres during drying, and
the elastic elongation or compression of flexible polymer to compensate the volume
shrinkage of latex particles. (a) A saturated colloidal dispersion with face-centered
cubic close-packed structure. In this case, the volume occupied by the colloidal
spheres is ca. 74% and that by water is ca. 26%. (b) There is volume shrinkage of the
latex spheres during drying, and it is supposed that the extending of infiltrated
PNIPAm into the latex interstices could compensate for the volume shrinkage and
minimize the resultant tensile stress. The volume of PNIPAm should be the sum of the
volume occupied by water and the volume freed by the shrinkage of the colloidal
spheres. Based on the statistical result of latex shrinkage in radius ca. 10 % (c), it is
calculated that the critical ratio of PNIPAm/colloidal spheres is 0.85:1.
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Critical stress during the assembling process of the latex particles.
Figure S7. (a) Relationship of the Rp0.2 of the Al foils with different thickness. (b) The
relationship between the thickness of PCs and their numbers of layer. Colloidal PCs
without cracks may be obtained when the thickness of PCs is lower than ~5.6 μm.
The formation of PCs without cracks could mainly be attributed to the completely
release of the tensile stress during assembled process. The critical stresses for
nucleation of a crack in a film of identical elastic spheres were calculated using
Griffith’s energy balance concept 1:
σc R
Wherein, R is the particle radius (2R = 310 nm), γ is the solvent-air surface tension (γ
= 0.072 N/m), h is the film thickness at cracking, G is the shear modulus of the
particles (1.6 MPa), M is the coordination number, and Φr is the particle volume
fraction.
In our case, the volume fraction is ca. 0.74, M = 6.5 and the observed film thickness at
cracking is ca. 19.7 µm; the calculated tensile stress is 110.6 MPa.
Reference:
1 Singh, K. B. & Tirumkudulu, M. S. Cracking in drying colloidal films. Phys. Rev.
Lett. 98, 218302 (2007).
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Crack-free PCs assembled on other metal substrates, such as Cu, Ti and Ni.
Figure S8. SEM images of PNIAm- Poly(St-MMA-AA) composite opal PCs
assembled on metal foil substrates, (a) Ti foil with thickness ≤ 35 μm, (b) Cu foil with
thickness ≤ 105 μm and (c) Ni foil with thickness ≤ 55 μm. The scale bar is 20 μm (the
inset scale bar is 1 μm). Crack-free colloidal PCs could be fabricated on other flexible
metal foil substrates beside Al foil, such as Ti, Cu and Ni foil, suggesting that the
method is versatile and general.
The critical thickness for crack-free PCs.
Figure S9. PCs with different thickness of (a) 1.1 μm, (b) 2.3 μm, (c) 4.4 μm, (d) 5.6
μm, (e) 7.3 μm and (f) 7.7 μm assembled on 100 μm-thick-Al-foils. The critical
crack-free PC thickness is determined to be ~ 5.6 μm. (Scale bar: 10 μm)
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Figure S10. (a) DSC and (b) TGA characterization of the composite PC material scratched off
from the Al foils. No characteristic peak of ice melting at ~ 0 oC related to water sorption on the
polymer DSC thermogram or thermal degradation at ~110 oC related to water loss in the TGA
curve was observed, indicating the water content in the obtained composite PC was negligible.
The thermal degradation at ~400 oC in the TGA curve was resulted from PS decomposition.
Figure S11. (a) The UV-Vis spectra of the large area PC films treated at temperature
of 120, 140, 160 and 180 oC . SEM images of the PCs after treated at (b) 160 and (c)
180 oC for 1 h.
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Figure S12. The influences of Rp0.2 of the Al foils and the weight ratio of
NIPAm/colloid on the fabrication of crack-free PCs. In the orange region, the
crack-free PCs could be achieved, wherein, the Rp0.2 of the used substrate is not higher
than 102 MPa, and the weight ratio of monomer/colloid is over the critical value of
1:1. In contrast, cracked PCs (cyan region) were obtained due to insufficient
infiltration of elastic polymer or a rigid substrate that could not be deformed to release
the stress.
Figure S13. SEM image of a cacked PC with thickness of 7.7 μm. Through the cracks,
the stretching of the polymer is obvious, which could absorb part of the generated
tensile stress in the assembly process.
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