Mesoscale Self-Assembly of Hexagonal Plates Using Lateral Capillary Forces:  Synthesis Using the “Capillary Bond”

Abstract

This paper examines self-assembly in a quasi-two-dimensional, mesoscale system. 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 these faces, and the densities of the three interacting phases (organic liquid, aqueous liquid, polymeric solid). Examination of all 14 possible combinations of hydrophobic and hydrophilic faces on the hexagonal plates led to three outcomes: (i) the extension of the strategies of self-assembly from the molecular to the mesoscale, (ii) the demonstration of a system in which small objects can be designed to self-assemble into a variety of arrays, and (iii) the hypothesis that capillary forces between objects can, in some circumstances, be considered to form the basis for a “bond” between themthe capillary bondand be used in synthesis in a way analogous to that in which noncovalent bonds are employed in molecular-scale synthesis.

Beyond molecules: Self-assembly of mesoscopic and macroscopic components

“…Capillary interactions (that is, forces resulting from minimizing the contribution of interfaces to free energies by minimizing interfacial areas) are particularly useful for these sizes and in these environments (38). For components floating at a liquid-liquid or liquid-vapor interface, the nature of the capillary interactions can be tailored by controlling the shape of the menisci at the interface between the components and the liquid (39).…”

Photovoltaic self-assembly.

“…[4][5][6][7][8][9][10][11][12] This concept of micro-PV placement via superhydrophobic-hydrophilic patterns uses chemical surface modifications of the substrate to divide it into hydrophilic and hydrophobic regions. Upon the introduction of a thin film of water onto this substrate, followed by the slow removal of the water, the resulting substrate will have regions containing water (hydrophilic) and regions without water (hydrophobic).…”

A Framework for Designing Novel Magnetic Tiles Capable of Complex Self-assemblies

“…Recent work in the field of macro-scale self-assembly include development of systems based on capillary interactions among millimeter-scale components either floating at a fluid-fluid interface or suspended in an approximately iso-dense fluid medium [1][2][3][4][5][6][7][8][9]. In fact, this technique has been adopted commercially [10,11].…”