Superhydrophobic Polydimethysiloxane Coatings Prepared by the in Situ Growth of Silicone Nanofilaments on a Sanded Substrate

Abstract

Hypothesis: Hydrophobic silicone rubber is used as coatings that create hydrophobic properties for different surfaces. Silicone rubbers have high chemical and physical stability. Hydrophobic properties and resistance to creeping flow are unique features of silicone rubber coatings. The purpose of this research is to synthesize and assess silicone rubber and alter its surface wettability by roughening and modifying the surface using materials with low surface energies.Methods: Silicone rubber was first synthesized by hydrosilylation method in presence of a platinum catalyst, and subsequently coated onto polytetrafluoroethylene (PTFE) sheet as an example of a low surface energy substrate. In order to create roughness on the surface, industrial sandpapers were used of having grit sizes of 120, 220, and 400. In the next step, low surface energy silicon nanofilaments (SNF) were used to modify the desired surface, which were decorated on the surface of the sample through vapor deposition method. Findings: The SEM images show that the roughness density on the surface of the samples created by a 400-grit sandpaper is higher than that of a 220-grit sandpaper, and this sandpaper is also higher than that of a 120-grit sandpaper. Increasing the roughness density increases the static water contact angle (WCA) because in this case the Wenzel model is no longer dominant, and the hydrophobic mechanism follows Cassie Baxter theory. Due to the highest degree of roughness density created on the surface, the PTFE substrate treated with a 400 grit sandpaper was used for the next stage of silicone rubber coating and finally for the growth of SNF on top of the silicone layer. Applying SNF coating on the sample surface leads to a significant increase in the WCA (~159°). This hydrophobicity enhancement after SNF coating can be attributed to the low surface energy of the coating and the increase in roughness caused by the random growth of nanofilaments.

Keywords

• superhydrophobic coatings
• polydimethylsiloxane
• silicone nanofilaments
• chemical vapor deposition
• surface roughness