Seedless assembly of colloidal crystals by inverted micro-fluidic pumping

TL;DR

This paper introduces a seedless, micro-fluidic pumping method to assemble large, oriented colloidal monolayer crystals at specific locations on a charged substrate, using ion exchange resin-induced fluid flow.

Contribution

It presents a novel seedless assembly technique leveraging ion exchange resin-driven fluid flow to control colloidal crystal formation and orientation.

Findings

Millimeter-sized monolayer crystals achieved with a single inverted pump.

Controlled crystal orientation along the line connecting two pumps.

Patterned ion exchange resins enable complex colloidal crystal patterns.

Abstract

We propose a simple seedless approach to assemble millimeter sized monolayer single colloidal crystals with desired orientations at predetermined locations on an unstructured charged substrate. This approach utilizes the millimeter-ranged fluid flow on the bottom glass substrate induced by an ion exchange resin (IEX) fixed on top of the closed sample cell. This fluid flow increases with decreasing height of the sample cell and increasing radius R of the IEX. For a single inverted pump, millimeter sized monolayer single crystals of hexagonal close packing can be obtained. For two closely spaced (D ~ 4R) pumps, the formed crystals have a predefined orientation along the line connecting the two IEX. By patterning IEX into different structures, colloidal crystals of different complex patterns form. The present method paves a convenient way for fabricating high quality monolayer colloidal crystals for a variety of applications.