Inkjet-Printed Polymeric Microstructures in $n$-Sided Regular Polygonal Cavities

We demonstrate an inkjet-based microfluidic technique as droplet vaporization deposition (DVD) that can be applied in the incorporation of hydrophobic substrates with microcavities to generate individual polymeric structures. Using soft-lithography method, the SU-8 and polydimethysiloxane were patterned to form various polygon-shaped cavities (side length ~200-700 μm and depth ~ 25-110 μm) which acted as micromolds (templates) for forming the shapes of the droplets deposited. With aqueous polyurethane droplets generated (single volume ~381 pL), the novel various microstructures in polygonal (tri- to hexagonal) forms were created through the deposition and evaporation processes and characterized with exotic performances in optics such as those of microlenses and micromirrors. Experimental and analytical results illustrated that the curved-surface (sinusoidal) topographies of the structures self-formed and detached from the underlying substrates were dominated by capillary action of fluid during evaporation. The merits over the existing techniques such as photolithography includes the one-step, low-temperature (ambient condition, ~1 atm at 25°C), and cost-effective (no waste materials) processes of solid formations. The successful formation of these structures suggests a new mechanism for self-releasing/detaching from the molds. As a reliable technique for the fabrication of such microstructures, the present DVD method presents an alternative method for various applications particularly including optical microelectromechanical system devices and parts used for assembly.