Patterned Colloidal Deposition Controlled by Electrostatic and Capillary Forces
[Under construction -- Nick Schade (fall 2009)]
The deposition and self-assembly of charged colloidal particles can be controlled using substrates chemically micropatterned with either positively or negatively charged regions. In this process, electrostatic forces first cause colloids to be attracted to the region of the substrate of the opposite charge. Then additional ordering of the colloidal particles occurs as the suspension dries due to lateral capillary interactions. This technique enables the fabrication of complex two-dimensional arrays of colloidal particles.
Authors: Joanna Aizenberg, Paul V. Braun, and Pierre Wiltzius.
Date: March 27, 2000.
Lucent Technologies, Bell Laboratories, Murray Hill, NJ 07974, USA
Physical Review Letters, vol. 84, no. 13, 2997-3000. 
Self-assembly on its own produces close-packed 2D and 3D arrays of colloidal particles rather easily. More complex patterns can be produced by aiding self-assembly through electrostatic forces, using a substrate that has charged regions arranged in very specific and controlled patterns. Microcontact printing can be used to chemically pattern a surface at the micron scale. The deposition of colloidal particles onto a patterned surface is called colloidal epitaxy.
Here the authors use self-assembled monolayers (SAMs) with ionic regions as templates for the deposition of charged colloids. The authors found that, as expected, the charged colloidal particles preferred to interact with regions of oppositely charged SAMs. The preference was particularly apparent when the substrate consisted entirely of positively or negatively charged SAMs, rather than including any neutrally-charged regions.