Thermally stable superhydrophobic and antibacterial PDMS/nano-PTFE coatings: A two-step spray method and TiO₂-enhanced performance

Superhydrophobic surfaces that retain their functionality after thermal stress are of great interest for self-cleaning and antifouling applications, offering enhanced durability. Herein, we compared one-step and two-step spray-coating methods for preparing nanocomposite coatings based on polydimethylsiloxane (PDMS) and polytetrafluoroethylene nanoparticles (nano-PTFE) on steel substrates, emphasizing how the coating architecture influences morphology, wettability, thermal stability, and bacterial adhesion. Based on morphological analysis, the one-step route produced sparsely exposed nano-PTFE at the surface, resulting in water contact angles (WCAs) of 100°–120° and sliding angles (SAs) of 35°–45°. The two-step method resulted in a dense coverage of nano-PTFE and hierarchical micro/nanostructures, which facilitated Cassie-type wetting and superhydrophobicity (WCA = 158°, SA = 5°). Incorporation of nano-TiO₂ into the two-step coating further increased surface porosity and raised the WCA to 163°, and decreased the SA to 2°. Under repeated high-temperature cycling at 120 °C, the PDMS/nano-PTFE coating lost superhydrophobicity after ∼70 cycles, whereas the TiO₂-loaded coating preserved self-cleaning behavior beyond 100 cycles. Bacterial adhesion assays (reported as log CFU/cm²) showed 1.5-log (∼96.8 %) and 2.2-log (∼99.4 %) reductions compared to bare steel for the PDMS/nano-PTFE and PDMS/nano-PTFE/TiO₂ coatings, respectively. The antibacterial properties of superhydrophobic coatings were tested after successive heating cycles, and only the TiO₂-loaded coating maintained its antibacterial efficacy without a significant decrease. The obtained results elucidate the structure-wettability-durability relationships and highlight hierarchical nanoparticle architectures that yield thermally stable and antifouling surfaces, making them suitable for biomedical applications.