Formation of complex polymeric microstructures through physical self-organization and capillary dynamics

We present a generic way of forming various complex polymeric, microstructures using physical self-organization and capillary dynamics. A simple lithographic tool called capillary force lithography is utilized for this purpose, in which the pattern formation is driven by capillary force, not involving any external force or modification. In this method, a patterned polydimethylsiloxane mold is placed on a spin-coated polymer film on a substrate and then the temperature is raised above the polymer's glass transition temperature, allowing for a surface tension-driven flow. One-step and two-step applications of the mold lead to various microstructures in which wetting and dewetting as influenced by the mold channel width and the film thickness gives rise to the self-organization of the structures. The method can also be utilized to produce a polymer sheet with both sides patterned and these sheets can be laminated to generate multi-level structures. An intriguing aspect of patterning microsphere surfaces is also presented. The complex microstructures are not easily accessible by other methods, thus providing a simple and economic way of generating potentially useful templates for biomedical, microfluidic, and optical applications.