Mesoscale Self-Assembly: Capillary Bonds and Negative Menisci

This paper describes the self-assembly of hexagonal plates (with 2.7 mm wide sides) at the interface between perfluorodecalin (PFD) and water. All 14 different hexagons that can be made by permuting the number and location of the hydrophobic and hydrophilic faces were examined. The plates attracted one another by lateral capillary forces involving the menisci on the hydrophilic faces. The plates were made of poly(dimethylsiloxane) (PDMS) containing aluminum oxide and had a density of 1.86 g/cm3, close to the density of PFD (ρ = 1.91 g/cm3). This work complements a previous paper (Bowden, N.; Choi, I. S.; Grzybowski, B. A.; Whitesides, G. M. J. Am. Chem. Soc. 1999, 121, 5373) that examined the self-assembly of hexagonal plates of PDMS (ρ = 1.05 g/cm3) that had a density close to that of water, and were attracted through menisci on the hydrophobic faces. The arrays that formed from the heavy (ρ = 1.86 g/cm3) hexagons with a particular pattern of hydrophilic faces were analogous to the arrays that formed from the light (ρ = 1.05 g/cm3) hexagons with that pattern of hydrophobic faces.