Fabrication of superhydrophobic unplasticized poly(vinyl chloride)/nanosilica sheets using Taguchi design methodology

This study introduces a relatively simple technique for the manufacture of superhydrophobic coatings on polymeric surfaces. Plastics such as unplasticized poly(vinyl chloride) (UPVC) do not have a strong hydrophobic nature that is characterized by their low contact angles. Techniques of both increasing surface roughness and lowering surface energy are required to change their hydrophilicity to superhydrophobicity. In the present study, a coating of a low-surface-energy thermoplastic polyurethane (TPU) was spin-coated with chemically treated nanosilica to reduce the surface energy of UPVC. Nanosilica particles were embedded on the surface using a hot-press. Taguchi design was used to optimize multiple processing parameters. Samples spin-coated with 10 g L−1 nanosilica suspension in ethanol at a rate of 400 rpm for 5 s and then hot-pressed at 155 ∘C under 2 atm(203 kPa) for 4 min had a contact angle of ca 157∘ and sliding angle of ca 6∘,which are characteristic of superhydrophobic surfaces. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging showed that these superhydrophobic surfaces were highly rough with nanoscale features. Peel test and SEM analysis showed that silica nanoparticles embedded in the TPU coating were more stable than particles immobilized on UPVC sheet without TPU coating, proving that a layer of more flexible coating can improve the longevity of superhydrophobic surfaces manufactured using this facile method.