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

Abstract

This study introduces a relatively simple technique to manufacture superhydrophobic coatings on polymeric surfaces. Plastics such as unplasticized polyvinyl chloride (UPVC) do not have strong hydrophobic nature that is characterized by their low contact angles. Both techniques of 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 by chemically treated nano silica to reduce the surface energy of UPVC. Nano silica 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 nano silica suspension in ethanol at the rate of 400 rpm for 5 s and then hot-pressed at 155° C under 2 atm for 4 minutes had ~157° contact angle and ~6° sliding angle that are characteristic of superhydrophobic surfaces. AFM and 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.