Formation of aligned needle‐like crystals of 9,10‐dibromoanthracene in small droplets

Abstract

One‐dimensional micromaterials are potentially applicable in various technologies, including sensor fabrications. Variations in the sensing performance of such materials can be ameliorated by their regular arrangement. For example, the materials can be aligned unidirectionally. However, controlling both their orientation and spacing remains challenging. In this study, small evenly spaced droplets were aligned on a surface and the solvent in the droplets was then evaporated in air to obtain evenly spaced, aligned needle‐like crystals of the solute. The droplets were confined to the concave portions of regular wrinkles formed due to buckling instability on a polydimethylsiloxane (PDMS) rubber surface. However, crystallization in small droplets with diameters of less than 100 μm was difficult to achieve because the probability of nucleus formation in each droplet was very low. To address this drawback, nuclei were added to the droplets externally, obtaining well‐aligned needle‐like crystals of 9,10‐dibromoanthracene (DBA), an organic semiconductor. The advantages of this method include its simplicity, cost efficiency, and applicability to fragile materials, because the application of mechanical force to the needle‐like crystals is not required.