Optical and physical properties of iridescent photonic crystals obtained by self-assembled polymethyl methacrylate nanospheres within graphene oxide nanoplatelets

Opal photonic crystals prepared by vertical templating of polymethyl methacrylate (PMMA) nanospheres in aqueous graphene oxide (GO) solutions were successfully obtained. The results show that increasing the PMMA nanospheres' size leads to the modification of the d-spacing in GO nanoplatelets, inducing brilliant iridescence colors that span the entire visible electromagnetic spectrum. Scanning electron microscopy study shows a uniform distribution of GO nanoplatelets on the surface and the bulk of the opal photonic crystals. The reflectance spectra exhibit a significant red shift from 385 to 660nm when the nanospheres' size increases from 160 to 306nm, respctively. The Raman spectra show a systematic decrease in the intensity ratio of the D to G bands of GO (I-D/I-G), suggesting a partial reduction of graphene oxide with decrasing the extent of defects in the partially reduced GO nanoplatelets. This finding is confirmed by the significant decrease observed in the intensity of the hydroxyl band in the attenuated total reflectance mode-Fourier transform infrared spectra of the photonic crystals. The results provide the first demonstrated example of intercalated assemblies of polymer nanospheres within GO nanosheets, leading to photonic crystals with brilliant iridescence colors that span the entire visible electromagnetic spectrum and can be tuned only by varying the size of the PMMA nanospheres.