Abstract
We demonstrate the potential of thermoresponsive poly N-(isopropylacrylamide) (PNIPAM) based surfaces in achieving a low-energy approach to modulate surface wetting for applications such as fog harvesting and anti-fogging. Alternative to grafting methods, we use a two-step approach for tuning the response amplitude. First, we blend PNIPAM with a chemically non-reactive poly (vinylidene fluoride), PVDF (1/3, 1/1, 3/1 by weight). Second, thermal nanoimprint lithography is used to create micro (3, 5, 10, and 20 mu m) and nano-scale (100 and 200 nm) pillars. Nano-patterned surfaces show a response amplitude of similar to 30 degrees-50 degrees compared to similar to 15 degrees-30 degrees, observed for the micro-patterned surface. X-ray photo-electron spectroscopy and energy dispersive X-ray analysis confirms the reduction of polyvinylidene fluoride phase domains and enrichment of PNIPAM on the nano-patterned surface. A real-time dynamic mist condensation study showed that the nano-patterned blend exhibited a lower temperature range (34/41 degrees C) for on/off (wetting/drying) state compared to an unpatterned blend (37/50 degrees C).