Macroscopic, Hierarchical, Two-Dimensional Self-Assembly
Author(s): Choi, Insung S., Ned Bowden, George M. Whitesides
Journal: Angew. Chem. Int. Ed. (1999) 38(20): 3078-3081.
Abstract:
Herein we demonstrate the operation of a hierarchy of interactions in the two-dimensional self-assembly of hexagonal poly(dimethylsiloxane) (PDMS) plates at a fluid - fluid (perfluorodecalin (PFD)/water) interface. The work uses molecular chemistry at surfaces to control menisci and hence interactions: the work has a strong chemical component, but extends from molecular interactions to interactions at surfaces and between materials and then to meso-scale objects. These objects interact through capillarity, that is, by minimizing the surface area of the PFD/H2O interface. We controlled the faces of the objects that are attracted to one another by patterning them to be hydrophobic or hydrophilic. Lateral capillary interactions can hold millimeter-sized objects through contacts that are sufficiently strong to withstand modest shear. The hydrophobic faces have large, positive menisci (the maximum height of the menisci is approximately the height of the faces for the objects used) and these faces are strongly attracted to one another. The hydrophilic faces have small, negative menisci (the maximum height of the menisci is <40% of the height of the faces) and these faces are weakly attracted to one another. Faces having positive menisci are repelled by faces having negative menisci. We have called the attractive interactions between menisci having the same sense (positive or negative) relative to the interface capillary bonds, in loose analogy to chemical bonds.