The wettability of a material is dependent on both its physical and chemical characteristics. If a liquid spreads completely across the surface of a material and forms a film, the contact angle, θ, is close to 0 degrees)(°). If the liquid beads on the surface, the surface is considered to be non-wetting. For water, the substrate surface is considered to be hydrophobic if the contact angle is greater than 90°. Certain applications may require a hydrophobic coating with a high contact angle of at least 150°. These coatings may be said to be superhydrophobic.
Surfaces patterned with alternating (binary) hydrophobic-hydrophilic regions offer a template for efficient fluid collection and management technologies. Micro-fluidic channels and wettability micro-patterns produced from various photodegradation techniques of hydrophobic chemistry or plasma chemical approaches provide avenues for producing various forms of hydrophilic micropatterns on hydrophobic surfaces. However, most patterning techniques require the use of masks (e.g., plasma chemical, photodegradation techniques, photo-induced techniques, UV-irradiation) or closed environmental chambers. Masks limit the flexibility in changing the type of pattern during the process, while chambers limit scalability and increase the patterning costs. Finally, in some superhydrophilic patterning techniques, the property is not permanent. Such coatings also require large concentrations of filler particles to attain superhydrophilicity, which may reduce their adhesion and durability as compared with other coating systems.
A non-toxic, environment friendly process for forming surfaces with binary hydrophobic-hydrophilic regions is desired. Compared to other organic-based approaches, advantages of such a process will include inherent thermal stability and scalability to large-area applications.