Patterned Colloidal Deposition Controlled by Electrostatic and Capillary Forces

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[Under construction -- Nick Schade (fall 2009)]

Light micrographs from Aizenberg paper.
Figure 1. Deposition of charged colloidal particles controlled by micropatterned ionic self-assembled monolayers. (a) Positively charged spheres attach to negatively charged regions of a wet template. The inset shows a scanning electron micrograph of the substrate geometry. (b) The structures focus due to capillary forces as the template dries. (c) Positively charged colloids deposited from a 0.005M LiCl solution. (d) Negatively charged spheres attach to positively charged regions.

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.

General Information

Keywords: colloid, self-assembly, charged interfaces

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. [1]

Summary

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.

Connection to soft matter