Nano-microstructured, superhydrophobic and near-infrared antireflective thin films on glass

Superhydrophobic surfaces were produced on glass with self-cleaning and wide-angle anti-reflection in the near-infrared (1.0-2.1 mu m). These properties resulted from a combination of surface energy and nano/micro-structured topology based on silica nanoparticles (NPs), index grading and interference. In a two-layer approach (glass/silica NPs/PTFE), a water contact angle (WCA) of 169 degrees+/-2 degrees was attained with very low hysteresis (<= 2 degrees), as well as high transmittance (93-94% at normal incidence). In a three-layer approach (glass/silica NPs/silica aerogel/PTFE), surfaces were produced with WCA of 158 degrees+/-2 degrees, also very low hysteresis (< 5 degrees), and significant antireflection. This allowed for a normal transmittance of 99.5% or higher, which decreased less than 2% at +/-20 degrees incidence. These results show that pronounced wide-angle antireflection and self-cleaning properties can be simultaneously attained by proper glass coating. Present advantages and limitations for potential applications are discussed.