Figure 2: On-the-fly alteration of particle height with inert flows.
From: Non-polydimethylsiloxane devices for oxygen-free flow lithography
(a) Schematic of microparticle synthesis in gas-impermeable NOA channel. Particles were synthesized and then carried out of the synthesis area using rapid, synchronized cycles of shutter-mediated ultraviolet exposure and pressure-driven flow. The vertical flow focusing process is precisely described in Supplementary Fig. S4. (b) Modified hydrodynamic resistance model used to determine hydrodynamic resistances of various segments of synthesis channel and to estimate volumetric flow rates from inlet pressures. We created three specific hydrodynamic cases: Q1≠0, Q2, Q3=0 (Top), Q1, Q3≠0, Q2=0 (Middle), and Q1, Q2≠0, Q3=0 (Bottom). We then measured inlet pressures that satisfied each case and generated a resistance diagram to extract hydrodynamic resistances (Supplementary Fig. S6). The process is explained in detail in the Methods Section. (c) Comparing modified hydrodynamic model with the previous model in achieving the symmetry condition (Q1=Q3). To visualize the symmetrical inert layers, three-layered particles were synthesized in a PDMS channel. When P2 was fixed to 3.0 psi, P3 satisfying the symmetry condition at a specific P1 (=4.9 psi) was predicted from each model. Symmetrical particles were prepared by the use of inlet pressures predicted from the modified model. (d) Particle height as a function of P1. Height of cylindrical particles was seen to vary with inlet pressures in a manner that matched predictions from the hydrodynamic resistance model. As shown in the graph, the Hm prediction compared well with measurements of particle heights. Scale bar, 10 μm.
