From nanospheres to microribbons: Self-assembled Eosin Y doped PMMA nanoparticles as photonic crystals.

A modified emulsion synthesis of poly(methylmethacrylate) (PMMA) with the Eosin Y (EY), commercial chromophore, yields dye doped polymeric nanoparticles (PMMA@EY). A systematic investigation on the experimental parameters (monomer and initiator concentration, reaction time and MMA/EY molar ratio) has been explored to modulate physico-chemical properties of the dye doped polymeric colloids. Spherical shaped particles, doped with EY (0.5-3.0 wt%; loading efficiency η = 11-15%), with controlled diameters in the range 240-510 nm, low dispersity and ζ-potential values in the range between -42 mV and -59 mV, have been synthesized and characterized by means of UV-Vis spectrometry, Dynamic Light Scattering (DLS), laser Doppler electrophoresis and Scanning Electron Microscopy (SEM). Microribbons based on PMMA@EY nanoparticles have been fabricated by room temperature self-assembly of aqueous colloidal suspension on highly wettable glass substrates. Surface chemical treatment assisted the formation of long (up to few centimeters) regular ribbons with rectangular section. Lateral size and height of the structures have been controlled by changing the suspension concentration and/or the deposition volume: the higher suspension concentration produces larger and thicker ribbons and the higher deposited volume produces thicker ribbons (up to 23 μm with 198 μL of a 3 wt% suspension). Moreover, a transition from a film-like to a ribbon-like growth has been observed with increasing nanoparticles concentration. Short range ordering and photonic crystal features have been maintained in the fluorescent ribbon microarchitecture, resulting in a self-assembled material with excellent potential for the development of mirror-less and random lasers.