Demonstrating use of continuous flow microfluidics to assemble colloidal particles on porous substrates

Self-assembly of colloidal particles for ‘bottom-up’ fabrication of various patterns and structures is critical for a range of applications including, but not limited to, energy migration, material science, biomimetics, and biosensing. Multiple self-assembly techniques, such as substrate templating — via topological or chemical patterning — and solvent evaporation were discussed in our previous papers and have been developed for the deposition of patterned self-assembled structures, such as bands of colloidal particles, on various substrates. While the templating techniques are limited due to the requirement of pattern-specific, prior substrate engineering to fabricate the desired structure, solvent evaporation requires longer assembly times and precise control over environmental conditions. In this paper, a template-free process, which is facilitated by continuous solvent drainage through porous substrates, is demonstrated for the self-assembly of colloidal particles into high-aspect ratio (>10³, length to height) structures, such as linear arrays or grid structures. Colloidal particles were assembled both on polymeric and metallic porous membranes, with assembly times up to ~ 10^{- 2} seconds per unit structure.