© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 5519 www.advmat.de www.MaterialsViews.com COMMUNICATION wileyonlinelibrary.com Adv. Mater. 2011, 23, 5519–5523 A. Honglawan, M. Cavallaro, Prof. K. J. Stebe, Prof. S. Yang Department of Chemical and Biomolecular Engineering University of Pennsylvania Towne Building, 220 South 33rd Street, Philadelphia, PA 19104, USA E-mail: shuyang@seas.upenn.edu D. A. Beller, Prof. R. D. Kamien Department of Physics and Astronomy University of Pennsylvania 209 South 33rd Street, Philadelphia, PA 19104, USA E-mail: kamien@physics.upenn.edu Prof. S. Yang Department of Materials Science and Engineering University of Pennsylvania 3231 Walnut Street, Philadelphia, PA 19104, USA DOI: 10.1002/adma.201103008 Self-assembly, self-processing, and bottom-up design are ever more important tools for the development of new materials of both fundamental and technological interest due to their robust capability for generating complex, hierarchical structures. In general, self-assembling materials, including colloids, block copolymers, and supramolecules or DNA form thermodynami- cally stable structures over a broad range of length scales, from the micro- to nanoscales. Structure formation in these long- range ordered phases is often governed by entropic and geo- metric considerations, leading frequently to a limited variety of optimal, close-packed structures. However, close-packed struc- tures are not always appropriate in device applications. Some control has been gained through so-called graphoepitaxy, which exploits substrates with topological [1–5] or chemical [6] surface relief patterns that nearly match the domain structures of block copolymers, for instance, and direct their epitaxial assembly into nanostructures with long-range positional order and ori- entation in thin films. However, epitaxial assembly of highly ordered square arrays has only been recently achieved in both triblock copolymers [7,8] and supermolecular assemblies of hydrogen-bonding diblock copolymer in thin films. [9] Because of their geometrical, mechanical, and electronic anisotropy, liquid crystals (LCs) are not only highly sensitive to external aligning fields but can also exquisitely control the propagation of electromagnetic phenomena. Consequently, the patterning of LC molecules has long been of interest for scientific discovery and technological advancement. Smectic-A (SmA) LCs are characterized by arrangement of molecules into layers with the long molecular axis parallel to the layer normal. When the surface chemistry promotes planar alignment of LC molecules, SmA LCs spontaneously form highly ordered hexagonal arrays of toric focal conic domains (TFCDs) [10] in which smectic layers wrap around a pair of dis- clination lines formed by a circle and a straight line passing through the circle center. In surface measurements, a defect domain appears as a circular, cone-shaped dimple at the LC/ air interface. The bending of the LC layers away from the flat equilibrium SmA to form TFCDs results from the com- peting effects of planar anchoring at the LC/substrate inter- face and homeotropic anchoring at the LC/air interface. In the standard smectic ground state, the smectic layers are flat and parallel to the substrate and thus the molecular orienta- tion points normal to both the LC/air and LC/substrate inter- faces. The TFCDs form spontaneously when the decrease in surface energy obtained by planar anchoring on the substrate outweighs the elastic energy cost of bending the layers and the increase in surface energy due to the dimple-like deformation of the LC/air interface. Regular hexagonal lattices of TFCDs have been used to create microlens arrays, [11] matrices for the self-assembly of soft microsystems, [12–14] lithographic templates, [15] 2D charge transport models, [16] and patterned func- tional surfaces. The ability to control the size and arrangement of TFCDs is currently under investigation; for instance, studies have employed substrates presenting different surface chemis- tries, [16–19] confinement within 1D microchannels, [16,20–23] and randomly patterned planar and depressed substrates. [24] Little is known, however, about a higher level of control of TFCDs into three dimensions. [25,26] Controlling topological defects and smectic LC phases in three dimensions is of particular interest to the generation of blue phases and other topologically struc- tured materials, which will lead to possibly disruptive display technologies. Here, we demonstrate the epitaxial assembly of SmA LCs into arrays of TFCDs with variable sizes and arbitrary symmetries (e.g., a square lattice) directed by pillar arrays. We utilize materials that induce planar anchoring of LC molecules, such as SU-8, a bisphenol A epoxy derivative. By varying the pillar dimensions (size, height, and spacing) and thickness of the LC film, we can confine and direct the growth of each TFCD. As a result, we promote a new variety of TFCD arrays beyond the close-packed hexagonal arrangement formed spontaneously on a flat surface by controlling the size and symmetry of the underlying pillar pattern. We hope that this template-directed assembly method will benefit a number of engineering applica- tions and advanced device concepts. The LCs used here are rigid biphenyl molecules with semifluorinated chains (see chemical structure in Figure S1, Supporting Information). They have a smectic-A LC phase at ≈114 °C, and retain TFCD structure when quenched to Apiradee Honglawan, Daniel A. Beller, Marcello Cavallaro, Randall D. Kamien,* Kathleen J. Stebe, and Shu Yang* Pillar-Assisted Epitaxial Assembly of Toric Focal Conic Domains of Smectic-A Liquid Crystals