Mesoscale self-assembly of hexagonal plates using lateral capillary forces: Synthesis using the "capillary bond"

This paper examines self-assembly in a quasi-two-dimensional, mesoscale sys tem. The system studied here involves hexagonal plates ("hexagons") of poly (dimethylsiloxane) (PDMS; 5.4 mm in diameter, 0.9-2.0 mm thick), with faces functionalized to be hydrophilic or hydrophobic, floating at the interface between perfluorodecalin (PFD) and H2O. The hexagons assemble by capillary forces originating in the interactions of the menisci at their hydrophobic and hydrophilic rectangular faces. The strength and directionality of the interactions can be tailored by manipulating the heights of the faces, the pattern of the hydrophobic faces, the pattern of hydrophobic regions on the se faces, and the densities of the three interacting phases (organic Liquid , aqueous liquid, polymeric solid). Examination of all 14 possible combinat ions of hydrophobic and hydrophilic faces on the hexagonal plates led to th ree outcomes: (i) the extension of the strategies of self-assembly from the molecular to the mesoscale, (ii) the demonstration of a system in which sm all objects can be designed to self-assemble into a variety of arrays, and (iii) the hypothesis that capillary forces between objects can, in some cir cumstances, be considered to form the basis for a "bond" between them-the c apillary bond-and be used in synthesis in a way analogous to that in which noncovalent bonds are employed in molecular-scale synthesis.