Dynamic Microfluidic Synthesis of Zinc Oxide Nanowires: Impact of Channel Architecture on Growth Homogeneity and Uniformity

Abstract

Zinc oxide nanowires are synthesized in situ within microfluidic reactors in dynamic mode owing to the continuous flow of the growth solution. The synergistic effect of fluid flow and confined volume enables fast synthesis, in 8–16 min only, while 2–3 h are needed in static mode synthesis. However, the co-integration of nanomaterials into microfluidic reactors poses challenges for their use as functional devices. Here, the issue of homogeneity of nanowire growth as well as the corresponding uniformity of the nanowire dimensions are addressed. This is demonstrated that the use of optimized tree-branched microchannel networks enables excellent homogeneity, quantified by a surface coverage of 99% across the whole area of the microfluidic reactor chamber, while it is limited to 55%–78% when using conventional microfluidic chambers. The latter also leads to severe non-uniformity of the nanowires, eventually resulting in radical changes in their morphology. On the contrary, the tree-branched microchannels lead to outstanding uniformity of the nanowires: their average diameters of 35 nm are almost constant within ± 1 nm across the whole chamber; the corresponding nanowire average length of 420 nm varies within ± 12 nm only. The proposed approach is applicable to a wide variety of other nanomaterials synthesis.