View source for Mesoscale Self-Assembly: Capillary Bonds and Negative Menisci

Zach Wissner-Gross (February 23, 2009)

==Information==
Mesoscale Self-Assembly: Capillary Bonds and Negative Menisci [http://pubs.acs.org.ezp-prod1.hul.harvard.edu/doi/full/10.1021/jp993118e]

Ned Bowden, Scott R. J. Oliver, and George M. Whitesides

The Journal of Physical Chemistry B, <b>2000</b>, 104 (12), 2714-2724

==Soft matter Keywords==
Capillary forces, self-assembly, menisci, capillary length

==Summary==
In their paper, Whitesides and coworkers float a layer of millimeter-sized PDMS [http://en.wikipedia.org/wiki/Polydimethylsiloxane] hexagons between perfluorodecalin (PFD) and water. They further pre-treat different edges of the hexagons, making them either hydrophilic (by oxidizing the edges with a plasma cleaner) or hydrophobic (by protecting the edges from oxidation with an additional cured layer of PDMS). By carefully agitating the solutions, the authors are able to induce self-assembly over the course of minutes to hours, and observe how structure varies with different patterns of hydrophobicity/hydrophilicity.

This article was written as a sister article to another publication [http://pubs.acs.org.ezp-prod1.hul.harvard.edu/doi/full/10.1021/ja983882z]. In that paper, the authors used PDMS with a density of 1.05 g/cm<math>^3</math>, barely greater than than of water. Here, the authors load their PDMS hexagons with aluminum oxide to a density of 1.86 g/cm<math>^3</math>, just less than that of PFD. The authors spend much of the paper discussing the theoretical and experimental differences observed between these two setups (i.e., in which case hydrophilic or hydrophobic interactions dominate). But, as the authors conclude in their abstract: "The arrays that formed from the heavy (1.86 g/cm<math>^3</math>) hexagons with a particular pattern of hydrophilic
faces were analogous to the arrays that formed from the light (1.05 g/cm<math>^3</math>) hexagons with that pattern of hydrophobic faces."

==Soft matter discussion==
The paper is really composed of two parts: <i>why</i> the hexagons self-assemble, and <i>what</i> structures they can assemble into. All the physics takes place is the former, so I will go through their discussion on why self-assembly occurs.

The physics behind self-assembly is shown in Figures 1 and 2.