Low-cost fabrication of flexible water-repellent film by spray coating of a hydrophobic nanoparticle dispersion

In this study, a low-cost fabrication method based on colloidal deposition was developed to prepare water-repellent coatings on PDMS-based flexible films. For this purpose, a lotus effect was induced by transferring micron-sized surface protrusions of commercial paper onto PDMS films by curing PDMS monomer on the paper and subsequently detaching the film after curing. The resulting rough PDMS surfaces were spray coated with hydrophobic silica nanoparticles to increase the contact angle of water droplets via the lotus effect. The surface roughness of the rough PDMS film after spray deposition of hydrophobic nanoparticles was confirmed using a surface profile tester. The hydrophobic nanoparticles were prepared by surface modification of silica nanopowder using a silane or titanate coupling agent and subsequent redispersion in an alcohol medium by sonication. Chemisorption of the coupling agents onto the nanoparticle surface was confirmed by Fourier transform infrared analysis. The maximum contact angle of water droplets in this study was greater than 145°, indicating a nearly superhydrophobic property of silica nanoparticle surfaces modified with the coupling agents with long-chain hydrocarbons or a perfluoroalkyl group redispersed in alcohol with low polarity.