Versatile reconfigurable glass capillary microfluidic devices with Lego® inspired blocks for drop generation and micromixing.

Novel cost effective, versatile, reconfigurable, reusable and easy to assemble glass capillary microfluidic devices were developed and used to generate micro/nano-materials with controlled size and morphology. The devices are composed of coaxial assemblies of glass capillaries held between two interchangeable plastic blocks fabricated from chemically inert polyoxymethylene copolymer using computer numerical control (CNC) machining. Three different blocks were combined and locked together using Lego® inspired stud-and-hole coupling system to achieve different flow configurations. The device allows a truly axisymmetric round capillary inside a round capillary geometry and self-alignment of capillaries. The synthesis of polyvinylpyrrolidone capped gold nanoparticles and liposomes of controlled size was demonstrated in the co-flow device by mixing the contents of two parallel laminar streams. The flow focusing device was used to generate piroxicam monohydrate crystals of controlled size (10-29 µm) by antisolvent crystallisation. Silver nanoparticles with tailored size (40-90 nm) were prepared in the three-phase device by merging silver nitrate and tannic acid/citrate streams inside droplets. The same device was used to prepare fluorescently labelled double emulsion droplets with controlled number of inner droplets. The droplet morphology was modified and tuned during operation by adjusting the distance between the inner capillaries. Water-in-oil emulsions consisted of Eudragit S100 solution at pH > 7 dispersed in Miglyol® 840 were prepared and gellified in situ over 6 h without fouling. The setup time of the novel devices was reduced from ∼30 min in manually made capillary devices to just several minutes.

Prediction and control of drop formation modes in microfluidic generation of double emulsions by single-step emulsification.

HYPOTHESIS: Predicting formation mode of double emulsion drops in microfluidic emulsification is crucial for controlling the drop size and morphology. EXPERIMENTS AND MODELLING: A three-phase Volume of Fluid-Continuum Surface Force (VOF-CSF) model was developed, validated with analytical solutions, and used to investigate drop formation in different regimes. Experimental investigations were done using a glue-free demountable glass capillary device with a true axisymmetric geometry, capable of readjusting the distance between the two inner capillaries during operation. FINDINGS: A non-dimensional parameter (ζ) for prediction of double emulsion formation mode as a function of the capillary numbers of all fluids and device geometry was developed and its critical values were determined using simulation and experimental data. At logζ>5.7, drops were formed in dripping mode; the widening jetting occurred at 5