Growth of micro-flowers behind hydrophobic polymer surface and impact of silver and tungsten oxide on the wetting characteristics

In this work, a simple and one-step process was demonstrated to develop hydrophobic polymer surfaces. Commercially available polycarbonate (PC) was treated to turn the front surface hydrophobic with an average wetting contact angle (WCA) as high as 110.5°. The formation of micro-flowers with a coverage density of 9.29 × 106/cm2 on the top of fine base nanostructures was confirmed by a high-resolution field emission scanning electron microscope (FESEM). Impact of typical metal and metal oxide such as silver (Ag) and tungsten oxide (WO3) deposited on such hydrophobic surfaces was demonstrated. Petals of micro-flowers and fine base nanostructures were well decorated with functional metals such as Ag and thus the front surface remained hydrophobic with an average WCA as high as 106.6°. Abundant sharp spikes on the top of narrow hills and dips as revealed in the high-resolution FESEM investigation, were speculated to be the reason behind this hydrophobic characteristic. On the other hand, the hydrophobic surface (WCA of ∼ 110.5°) turned hydrophilic (WCA of ∼11.7°) when the surface was decorated with functional metal oxides, such as WO3. Sessile drop tests were carried out to record average WCA and to understand the wetting characteristics of the specimens. A plausible mechanism for such hydrophobic characteristics as well as the transition from a hydrophobic state to a hydrophilic state has been elucidated.