Nano/microstructured polyhedral oligomeric silsesquioxanes-based hybrid copolymers: Morphology evolution and surface characterization

Unique micro-bean sprouts with nano-tails were electrohydrodynamically prepared from poly[(propylmethacryl-heptaisobutyl-polyhedral oligomeric silsesquioxane)-co-(methylmethacrylate)] (POSS-MMA). The nano/microstructured POSS-MMA substrates reveal superhydrophobic nature, with contact angles >160 degrees Contact angle versus time plots show that water droplet evaporation from the substrates with micro-bean sprouts falls into two stages: the initial stage, marked by steadily decreasing contact angles and the later stage, marked by rapidly decreasing contact angles. The turning point differentiating these two stages occurs at similar to 120 degrees-130 degrees. The substrates consisting of micro-bean sprouts with larger heads experience pinned triple-line phase during the early stage of droplet evaporation. In contrast, the triple line for a droplet placed on micro-bean sprouts with smaller heads can move easily, leading to a rapid decrease in contact diameter. Meanwhile, the contact angle decreases only slightly during the rapidly moving triple-line phase. The contact angles of the fibrous substrates measured during the initial stage of water droplet evaporation are much lower than those of micro-bean sprouts, even though the time period of the initial stage is extended. Both the architectures and the sizes of these POSS-MMA nano/microstructures were shown to affect the energy barrier for the triple-line motion during water droplet evaporation and therefore the contact angle hysteresis. (C) 2012 Elsevier Inc. All rights reserved.