Liquid crystallography: 3D microdroplet arrangements using microfluidics

Abstract

Monodisperse liquid particles (femtolitre oil droplets) are shown to self-organize into three-dimensional (3D) close-packed face-centered cubic (fcc) arrangements. Droplets were formed at a nanochannel–microchannel interface, and the formation of these arrangements occurred at certain flow-rate ratios of oil and water. The remarkably robust and stable structures formed in two different ‘crystallographic’ orientations of a face-centered cubic lattice, fcc(100) and fcc(111), as evidenced by the occurrence of square and hexagonal patterns at the plane adjacent to the channel wall. The orientation was found to depend on the oil-to-water flow-rate ratio. Similar to solid state crystals, ‘crystallographic’ features were observed, such as dislocation lines and defects. The 3D arrays presented in this work could provide platforms for a number of applications.