title: Easy route to superhydrophobic copper-based wire-guided droplet microfluidic systems.
abstract: Droplet-based microfluidic systems are an expansion of the lab on a chip concept toward flexible, reconfigurable setups based on the modification and analysis of individual droplets. Superhydrophobic surfaces are one suitable candidate for the realization of droplet-based microfluidic systems as the high mobility of aqueous liquids on such surfaces offers possibilities to use novel or more efficient approaches to droplet movement. Here, copper-based superhydrophobic surfaces were produced either by the etching of polycrystalline copper samples along the grain boundaries using etchants common in the microelectronics industry, by electrodeposition of copper films with subsequent nanowire decoration based on thermal oxidization, or by a combination of both. The surfaces could be easily hydrophobized with thiol-modified fluorocarbons, after which the produced surfaces showed a water contact angle as high as 171 degrees +/- 2 degrees . As copper was chosen as the base material, established patterning techniques adopted from printed circuit board fabrication could be used to fabricate macrostructures on the surfaces with the intention to confine the droplets and, thus, to reduce the system's sensitivity to tilting and vibrations. A simple droplet-based microfluidic chip with inlets, outlets, sample storage, and mixing areas was produced. Wire guidance, a relatively new actuation method applicable to aqueous liquids on superhydrophobic surfaces, was applied to move the droplets.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, Høgskoleringen 5, Trondheim NO-7491, Norway. mumm@phys.ntnu.no
authors.forename: Florian
authors.initials: F
authors.lastname: Mumm
authors.forename: Antonius T J
authors.initials: AT
authors.lastname: van Helvoort
authors.forename: Pawel
authors.initials: P
authors.lastname: Sikorski
mesh_terms: D000388:Air; D003300:Copper / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D046210:Microfluidic Analytical Techniques; D053770:Nanowires / Q000737:chemistry*; D010084:Oxidation-Reduction; D013499:Surface Properties; D013696:Temperature
chemical_list: D003300:Copper; C029892:cupric chloride