Electrohydrodynamic printing of pre-assembled colloidal particle structures*

Recent discoveries have shown that dilute suspensions of colloidal particles with diameters ranging from 200 nm – 1 µm can be assembled into distinct colloidal bands within microchannels (100 – 300 µm wide x 34 µm deep x 4 cm long). The band formation has been shown to require opposed Poiseuille and electrokinetic flows. Moreover, band formation occurs above a minimum applied potential (and consequently electric field) threshold at a given shear rate. Band formation is known to be a function of particle size, particle volume fraction, particle zeta potential, and the minimum electric field thresholds change in a non-linear fashion for particle mixtures. 

The colloidal bands present a unique, high throughput flow through system for assembling structures from pre-assembled high aspect ratio bands (~ O(10⁴)), vs. current state-of-the-art particle-by-particle assembly methods. In this work, we discuss the design, fabrication, and development of a microchannel nozzle that acts as a printer for pre-formed particle bands at a representative diameter of 490 nm on a soft substrate. The impact of various Poiseuille and electrokinetic flow conditions on the printing of particles to substrates outside the channels will also be discussed.