Colloidal Self-Assembly Templated by Fluid Interfaces

We present a method for assembling close-packed two-dimensional colloidal crystals by decreasing the height of a fluid oil-water interface. We show that the self-assembly is driven by lateral capillary interactions caused by the overlap of the deformed interfaces above the particles, and furthermore, that this deformation is a result of the disjoining pressure between the charged colloids and the interface. The rigidity of the self-assembled crystals is determined by the strength of the disjoining pressure, resulting in mechanical properties that range from reversible soft-crystals to solid-like crystals. Once the interface contacts the particles, the particles spontaneously transfer onto the interface due to the high three-phase contact angle. This final interfacial structure is consistent with long-range electrostatic interactions between particles confined to an oil-water interface (i.e. open hexagonal arrays). [1]

[1] B. J. Park, et al., Langmuir, 24:1686–1694, 2008.