Anthracene, an organic scintillator, is covalently incorporated into a poly(styrene-co-propargyl acrylate) basis through an emulsion copolymerization. The result is poly(styrene-co-propargyl acrylate-co-anthracene methyl methacrylate) (PS-PA-PAMMA) monodisperse copolymer nanoparticles that form an x-ray radioluminescent crystalline colloidal array (CCA). Coulombic forces cause the negatively charged particles to self-assemble into an FCC crystal structure. The CCAs exhibit pseudo bandgaps in which specific wavelengths of light, known as rejection wavelengths, are prohibited from propagating throughout the material. The rejection wavelengths of the CCAs are dependent on the interplanar spacing of the particles, indicating that adjusting the spacing tunes the pseudo-bandgap. The radioluminescence exhibited by the CCAs stems from the inherent scintillating properties of anthracene. When the rejection wavelength does not overlap the anthracene emission, the CCAs exhibit the typical radioluminescence characteristic of anthracene. Encapsulating the liquid CCAs in a poly(ethylene glycol) methacrylate (PEGMA) based hydrogel network stabilizes the crystal-like structure since the liquid CCAs are susceptible to ionic impurities and mechanical stress. The interplanar spacing of the CCA particles can be adjusted before or after hydrogel encapsulation. Diluting the liquid CCA with deionized water increases the interplanar spacing of the particles, effectively red shifting the rejection wavelength. The interplanar spacing of the CCA particles encapsulated in a hydrogel can be increased through swelling or decreased through drying the film. It was shown that when hydrogel films were dried so the rejection wavelength was blue shifted to overlap the anthracene emission, the emission was decreased. This indicates that by coupling the emission of the scintillator and the rejection wavelength of the CCA, the emission of the system can be tuned.

Hydrogel encapsulated radioluminescent crystalline colloidal arrays with tunable emissions

ACS Fall 2021

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