Low cost fabrication of a superhydrophobic V-grooved polymer surface.

Engineering of polymer surfaces to control their wetting properties has shown a wide range of potential applications. In this paper we show low cost fabrication of a superhydrophobic polymer surface via a hierarchical combination of hot embossing, O2 reactive ion etching (RIE) and deposition of a hydrophobic silane. The hot embossing and O2 RIE were used to produce respective micro and nanoscale surface roughness which is a requirement for obtaining superhydrophobic surfaces, while the deposition of a hydrophobic silane modified surface chemistry. In order to increase the water/air interface in the Cassie-Baxter composite wetting model, a brass mold with microscale V-grooves was used for hot embossing. Images of droplets in both static water contact angles and dynamic impact tests with the surface clearly show that the wetting state follows the Cassie-Baxter wetting model. The results of this study indicate that our design of the dual level surface roughness and the fabrication process allow for low cost and easy production of a highly superhydrophobic surface.

3D nanomolding for lab-on-a-chip applications.

The ability to decorate microfluidic channel walls with additional micro/nanostructures becomes important as a means to modify the flow behavior, such as mixing and pressure drop, as well as to enhance the reactivity of bio-reactions to the surface in lab-on-a-chip applications. Despite the ability of mass production at low cost, conventional micro and nanomolding techniques are limited to the patterning of planar or slightly curved polymer substrates. Here we show a two-step molding technique, named 3D nanomolding, which allows the patterning of arbitrarily hierarchical multiscale structures, even nanostructures formed on the vertical sidewalls of microfluidic channels. In the first molding step, an ultra-thin intermediate polydimethyl siloxane (PDMS) stamp is produced by spin-coating and curing PDMS prepolymer on a pre-nanopatterned poly(methyl methacrylate) (PMMA) substrate, which is followed by the second molding step using the primary PDMS stamp containing microstructures. Various hierarchical micro and nanostructures are demonstrated, which include a biomimetic superhydrophobic structure in a lotus leaf surface to modify the surface wetting property and microfluidic channels where the walls are patterned with nanostructures. Despite the presence of nanostructures on the top surface, 3D nanomolded microchannels could be sealed well with a nanopatterned PMMA cover plate using solvent bonding to form enclosed microfluidic devices. The results indicate that the 3D nanomolding technique is suitable for decorating microchannel walls for lab-on-a-chip applications.