Supporting information
Preparation of monodispersed P (St-MMA-AA) latex spheres
P (St-MMA-AA) spheres were synthesized according to the reported method with minor modification, using batch emulsion polymerization. In a typical procedure, emulsifier sodium dodecyl benzene sulfonate (SDBS, 0–0.011 mmol), the amount of which was lower than the critical micelle concentration (CMC), and buffer agent of ammonium bicarbonate (6.30 mmol) were dissolved in water, and MMA (10.00 mmol), AA (13.89 mmol) and St (182.60 mmol) were dispersed in 100 ml solution mentioned above. The mixture reacted at 70 ℃for 0.5 h. Following the addition of an aqueous solution of ammonium peroxodisulfate (APS, 2.12 mmol), the polymerization was carried out at 75 ℃for 10 h with continuous stirring. The resulting latex spheres were used directly without purification. The size and morphology of the microspheres was characterized using an H800 Transmission electron microscope (TEM) (JEM 2010, Japan).To determine the average diameter and size polydispersity from the SEM images, we measured 100 particles using the program iTEM (Olympus Soft Imaging Solutions GmbH). The resulted P(St-MMA-AA) latex nanospheres was 270 nm in diameter, the polydispersity was 0.02, as determined by scanning electron microscopy (SEM).
For P (St-MMA-AA) colloidal array, the reflection follows Bragg and Snell’s law (equ (1)) for the close-packed face-centered cubic lattice.
（1）
Where m is the order of reflection, λ is the wavelength of the reflected light, neff is the effective index (RI), θ is the angle between the incident light and normal to the reflection plane, and d111 is the distance between array planes that can be expressed as a function of the diameter D for P (St-MMA-AA) colloidal array:
(2)
Note that the effective refractive index of these core-shell latex is 1.45 and the incident light is normal (θ=180°) The monodisperse latex was prepared by one-step via batch emulsion polymerization. The mean diameter of P (St-MMA-AA) colloidal latex is 270 ± 5nm. P (St-MMA-AA) colloidal crystal metamaterials showing an orange structure color have a maximum reflection at 620nm.
The nucleation mechanism of the latex particles can be considered as a homogeneous nucleation mechanism. Accordingly, the hydrophilic of the comonomers that is the main polymerization factor influences the latex sphere morphology. For instance, outermost layer of the latex spheres was different from its interior, being enriched with polar groups35. Thus, the final morphology of composite latex spheres is expected to be a core-shell structure, confirmed by TEM images (Fig.1). Based on the polarity of the comonomers (St, MMA, AA) and relative polymers. PS domains are located in the core of the latex spheres, a thin shell is rich in PAA and PMMA which covers the PS core polymer with carboxyl groups anchored upon the surface of latex spheres, favoring the formation of hydrogen bonds among latex spheres. As shown in Fig.1, the dark PS regions are surrounded by a bright PMMA/PAA thin domain. These microspheres exhibited narrow size distribution with hard and hydrophobic PS being rich in their inner regions as well as soft and hydrophilic MMA-AA in their outer regions. The thickness of the shell was about 20 nm to 30 nm.
Furthermore, the hydrogen bonds of the carboxyl groups on the surface of the latex clarified by FTIR spectra. It is clearly observed that a broad band with a maximum at 3224 cm-1 was assigned to the hydrogen bonds among carboxyl groups. The peak at 1725 cm-1 belonged to C=O stretching. In addition, the peaks at 1461 cm-1 and 1183 cm-1 were attributed to the aromatic ring in styrene. The results showed that since the encapsulation of the PS core by the hydrophilic layer of PAA/PMMA, the core-shell structure formation for its deformation during a fully dense structure fabrication.
Figure S1 TEM image of P (St-MMA-AA) latex spheres
Figure S2 FTIR spectra of latex copolymer samples made by batch emulsion polymerization of St, MMA, and AA at 72 ℃
Figure S3 Reflectance spectra of P(St-MMA-AA) CCs self-assembled using 2.50 wt% of colloidal emulsions 5000 rpm RC with different centrifugal temperatures, 0 / 1 / 2 / 3℃.
Figure S4 (a) Digital photograph of the FCC P(St-MMA-AA) CCs. (b) The diameter of this P(St-MMA-AA) is 270nm. (c) SEM image of the cross section of the CCs. (d) Reflectance spectra of the optimization sample.