Assembly of uniform photoluminescent microcomposites using a novel micro-fluidic-jet-spray-dryer



Generation of uniform micro-particles containing (i) pure lactose; (ii) silica nanoparticles and lactose; (iii) silica nanoparticles/lactose doped with Eu(III) have been successfully achieved using a novel spray dryer with a uniquely designed microfluidic aerosol nozzle as the monodisperse droplet generator. Here we investigate the impacts of precursor compositions and concentrations, as well as the drying temperature profile on particle size, morphology, and surface element distribution. Distinct morphologies are observed with different precursor compositions, ranging from smooth spherical lactose microparticles to the buckled shape for composites containing silica nanoparticles. The formation of such morphology is qualitatively interpreted by using Peclet number, indicating that the presence of the suspended silica nanoparticles facilitates shell formation at the early stage of the drying process. As the drying continue, such shell is subject to buckling, induced by the capillary force due to the lower mechanical integrity inside the droplet. Post calcination, transmission electron micrographs of Eu(III)/silica nanoparticles/lactose microcomposites confirm the formation of nano-sized Eu2O3 homogeneously embedded on the silica shell. Photoluminescence spectra of these particles indicate that enhancement of photoluminescence intensity is directly related to the europium loading, which could be adjusted from the precursor composition. This work demonstrates a scalable route to assemble relatively complex composites with uniform properties, without extensive conjugation or purification steps commonly required in wet chemistry-based processes. © 2011 American Institute of Chemical Engineers AIChE J, 2011