Design Parameters and Principles of Liquid-Crystal-Templated Synthesis of Polymeric Materials via Photolithography

The design parameters and principles for the synthesis of polymeric microscopic objects using a method that combines photolithography and liquid crystal (LC) molecular templates have been demonstrated. Specifically, mixtures of a reactive mesogen (RM257) and nonreactive LC (E7) were polymerized using UV light and a photomask. We used photomasks with circular, triangular, rectangular, square, star-shaped, and heart-shaped features to provide initial shapes to the objects. Then, the unreacted parts were extracted and the polymeric objects were allowed to shrink anisotropically as defined by the ordering symmetry of the LC mixture. The initial configuration of the LC mixtures played a critical role in determining the final shapes of the polymeric objects formed after shrinking, which resulted in chiral twisting and bending, leading to more than 20 different shapes. We found that the pitch size of the bulk chiral twisted objects depends linearly on the angle of chiral twist of the LCs, whereas it was independent of their thickness and length ranging from 1.5 to 160 μm and 100 μm to 2.45 cm, respectively. The shapes of the polymeric objects synthesized from LC films with bent LC ordering, however, were critically dependent on the thickness of the objects due to the interplay between the elastic energy and surface anchoring of the LCs. The critical role of LC elasticity was observed for thicknesses below 20 μm, above which surface anchoring was dominant in determining the shapes. Overall, the proposed method was shown to provide a precise control over the three-dimensional architectures of the objects with size range that covers the micro and macro scales, which would find use in fields ranging from emulsion stabilization and catalysis to micromachines and artificial muscles.