3 years ago

Free-Standing Photonic Glasses Fabricated in a Centrifugal Field

Free-Standing Photonic Glasses Fabricated in a Centrifugal Field
Geoffroy J. Aubry, Lukas Schertel, Mengdi Chen, Danja Fischli, Georg Maret, Sebastian Polarz, Helmut Cölfen, Benedikt Häusele
One efficient method to obtain disordered colloidal packing is to reduce the stability of colloidal particles by adding electrolytes to the colloidal dispersions. But the correct amount of additional electrolytes must be found empirically. Here, the effect of CaCl2 on polystyrene colloidal dispersions is studied, and a link between the amount of CaCl2 and the corresponding glassy colloidal structure is quantitatively built. A threshold concentration of CaCl2 is found by dynamic light scattering. When exceeding this threshold, different nanoparticle oligomers are observed in the dispersions by analytical ultracentrifugation. The second objective is to achieve free-standing samples, which is required for many optical measurements. A universal method is established, using a centrifugal field to produce robust samples by polymerizing coassembled hydrophilic monomers to form a network, which traps the glassy colloidal structures. Photon time of flight measurements shows that the CaCl2 concentration threshold should not be exceeded. Otherwise an optical shortcut may take place. Thus, the work provides a feasible universal route to prepare macroscopic free-standing photonic glasses from electrostatically stabilized nanoparticles, suitable for further optical investigation. Free-standing photonic glasses are prepared with controllable disorder/structure by sedimentation in a centrifugal field for the first time. A proof of principle photon time of flight experiment demonstrates the good quality and promise of the obtained colloidal glasses. Previously, light localization phenomena have been predicted but never observed in 3D materials, largely due to very few satisfactory materials available for study.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/smll.201701392

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