Interfacial wetting behavior, tribological integrity, and antifouling functionality of h-BN/FEP nanocomposite coatings on stainless-steel heat exchanger surfaces

Abstract

The solid–liquid interface governs fouling deposition and frictional losses on heat exchanger surfaces, yet the interplay between coating nanostructure, interfacial wetting state, and long-term surface functionality remains poorly understood. In this study, fluorinated ethylene propylene (FEP) coatings reinforced with hexagonal boron nitride (h-BN) nanoparticles (0–10 wt%) were spray-deposited on AISI 316L stainless-steel substrates and characterized at multiple length scales using field-emission SEM, EDX elemental mapping, optical tensiometry, and surface profilometry. SEM imaging revealed that 7 wt% h-BN (FH7) produced a void-free nanocomposite surface with homogeneously dispersed nanoparticles, while 10 wt% loading caused agglomeration into 2–15 μm clusters. This microstructural difference dictated the interfacial wetting regime: FH7 sustained a Cassie–Baxter state with θ = 135°, whereas FH10 transitioned to the Wenzel regime (θ = 113°) due to macro-roughness-induced liquid penetration. Tribological testing (20 N, 500 m sliding) showed that FH7 achieved a friction coefficient of 0.21, 74.69% lower than that of the bare substrate, and retained full coating–substrate interfacial integrity, confirmed by post-wear SEM. In contrast, both FEP and FH10 coatings exhibited complete delamination at the coating–substrate interface through distinct failure mechanisms. The functional consequence of these surface and interface properties was assessed through 250-h fouling experiments: the uncoated surface showed approximately 82% more fouling accumulation compared to the FH7-coated surface, and a 95.25% reduction in fouling resistance factor was recorded on the FH7-coated surface compared to the uncoated surface. Most critically, the FH7-coated exchanger sustained only 2.76% thermal performance degradation over 250 h of continuous operation, compared with 42% degradation for the uncoated reference, delivering 38.22% higher heat transfer under fouled conditions at Re = 30,000. These findings demonstrate that nanoparticle dispersion quality at the surface–matrix interface governs a coupled wettability–tribology–antifouling performance cascade, establishing composition–interface–function design guidelines for durable hydrophobic nanocomposite coatings.