Facile fabrication of flexible superhydrophobic surfaces with high durability and good mechanical strength through embedding silica nanoparticle into polymer substrate by spraying method

Flexible superhydrophobic surfaces have been attracting more and more attention due to their foldable property. However, the superhydrophobic structure was easily damaged or destroyed owing to their poor interfacial force between substrate and superhydrophobic coating. Herein, fluorinated silica nanoparticles (F-SiO2) were sprayed onto the wet poly(amide–imide) (PAI) surface, which made F-SiO2 easily went into PAI substrate to enhance the durability of superhydrophobic surface. The PAI/F-SiO2 flexible surface exhibited a water contact angle (CA) of beyond 160° and a sliding angle (SA) of as low as 3°, while the tensile strength (34 MPa) was comparable to that of PAI substrate (35.8 MPa). Encouragingly, the superhydrophobicity and hierarchical porous structure of PAI/F-SiO2 surface were maintained even they were folded by 5000 times or underwent sandpaper abrasion test (500 cm of wear on a 1200 grit sandpaper under 50 g load), while the nanocomposites failed the sandpaper abrasion test when F-SiO2 were sprayed onto completely dried PAI surface. More importantly, the CA and SA just slightly decreased when PAI/F-SiO2 surfaces were heated at 300 °C for 24 h due to the unique surface morphology and high thermal stability of PAI, which is one of the highest thermal stabilities for flexible superhydrophobic films. In addition, PAI/F-SiO2 surfaces maintained superhydrophobic after hot water jet impact, acid–base immersing, UV irradiation, and ultrasonic treatment, indicating the fabricated surfaces could be used for practical application especially under harsh conditions. Furthermore, the superhydrophobic surfaces possessed icephobic properties. It should be noted that PAI/F-SiO2 surfaces showed such excellent properties, although their fabricating procedure did not undergo any optimization. This wet spraying method was also used to fabricate flexible superhydrophobic surfaces with other polymers as substrates such as poly(acrylic acid) (PAA), thermoplastic polyurethane (TPU), polystyrene (PS), and poly(vinyl alcohol) (PVA). Therefore, the simple strategy provided a general route to prepare flexible superhydrophobic films with high durability.