Three-dimensional self-assembly of millimetre-scale components

The spontaneous association of molecules, termed molecular self-assembly, is a successful strategy for the generation of large, structured molecular aggregates1. The most important source of inspiration for this strategy is the biological world, in which many processes involve interfacial interactions and shape selectivity that guide the formation of complex, multicomponent three-dimensional structures. The success of molecular self-assembly notwithstanding, many objectives in science and technology require the assembly of components that are much larger than molecules: examples include microelectronic and microelectro-mechanical systems, sensors and microanalytical and micro-synthetic devices2. Photolithography, the principal technique used to make such microstructures, has certain limitations: it cannot easily form non-planar or three-dimensional structures; it generates structures that are metastable; and it can be used only for a limited set of materials3. Here we describe an approach for the self-assembly of millimetre-scale components that uses two concepts to direct the assembly process: shape recognition and the minimization of liquid–liquid interfacial free energies4. These play a role in other spontaneous self-assembly phenomena, such as the formation of bubble rafts5,6, the patterned dewetting of surfaces7,8, and the coalescence of liquid drops9. We apply self-assembled monolayer molecular films10 to the surfaces of shaped macroscopic objects to render them hydrophilic or hydrophobic, depending on the terminal groups of the bound molecules. In aqueous solution, hydrophobic surfaces bearing a thin film of a hydrophobic, lubricating liquid adhere to similar surfaces with complementary shapes, while being able to adjust their relative alignment to ensure a good fit. In this way, the components assemble into well defined aggregates, which can be bound permanently when the hydrophobic liquid films consist of a polymerizable adhesive.