Surfaces exhibiting extreme wetting behavior with water, including both superhydrophobic and superhydrophilic behavior, have recently emerged as exciting new vehicles for controlling surface wettability. Such surfaces are typically created through a combination of surface texturing at the nano- and micro-scale and suitable surface chemistry. The highly versatile layer-by-layer assembly process used to fabricate polyelectrolyte multilayers is ideally suited for controlling surface topography and chemistry at both the molecular and the supramolecular level. As a result, a number of schemes have recently been put forth for creating polyelectrolyte multilayers that exhibit superhydrophobic wetting characteristics. A key element of both the superhydrophobic and superhydrophilic multilayers that we have developed is the establishment of porosity at either the micron-scale (superhydrophobic) or the nano-scale (superhydrophilic). Techniques to create patterned superhydrophobic/superhydrophilic surfaces provide new opportunities to create planar open microfluidic channels as well as fog-harvesting coatings that mimic the behavior of the Namib Desert beetle. Investigations of these patterned, extreme-wetting surfaces as cell and bacteria resistant coatings, anti-fogging/anti-reflection coatings and fog harvesting coatings look promising.
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