Nanopost-Guided Self-Organization of Dendritic Inorganic Salt Structures

The formation of hierarchical architectures is of fundamental importance and yet a relatively elusive problem concerning many natural and industrial processes. In this paper, a nanopost array platform, or a nanopost substrate, has been developed to address this issue through a model study of the drying structures of phosphate buffered saline (PBS) solution. Unlike on a plain surface, highly ramified salt structures are formed by simply allowing the nanopost substrate wetted with the salt solution to dry, a process that completes within minutes at room temperature. The branches of salt structures have similar shapes repeating at different length scales, ranging from similar to 200 nm up to a few centimeters in length, covering a 2 x 2 cm(2) area patterned with nanoposts fabricated in photoresist via laser interference lithography (LIL). Scanning electromicrograph (SEM) images show that salt structures are formed around nanoposts, and characteristic features of these salt structures can be modulated and predicted based on the surface properties and geometrical arrangements of nanoposts, suggesting that nanoposts can be used to guide the organization and crystallization of salts. This nanopost-guided crystallization approach is robust, rapid, versatile, and amenable to real-time observation and mass production, providing a great opportunity for the study and creation of large-scale hierarchical structures.