Inkjet-Printed CNT/PVA Membranes with Stable Cassie Superoleophobicity for High-Efficiency Oil–Water Separation

The fabrication of oil-repellent membranes has become an imperative requirement for building high-performance oil-water separation systems. Inkjet printing is a promising technology for this purpose due to its simplicity, efficiency, and scalability. However, the impact of substrate membrane characteristics on the oil-repellent performance of the fabricated membrane remains largely unknown. This study investigates inkjet printing as a scalable surface modification strategy to deposit carbon nanotubes (CNTs) and poly(vinyl alcohol) (PVA) on polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) substrates. Complementary surface analyses revealed substrate-driven deposition mechanisms: PVDF's smooth morphology enabled uniform CNT distribution (100% coverage at 133.0 mg m^-2), while PTFE's fibrous structure confined CNTs to pore regions, creating discontinuous CNT networks. Optimal performance was achieved with 1-cycle PVA on PVDF and 3-cycle PVA on PTFE. Under static conditions, the studied membranes exhibited oil repellency in the order of modified PVDF > modified PTFE > pristine PVDF > pristine PTFE. However, filtration of submicron oil droplets revealed the chemical heterogeneity of modified PTFE membrane; the adhesion of oil droplets to PTFE-exposed area disrupted the continuous water layer, resulting in accelerated oil contamination that surpassed pristine PVDF membranes. In contrast, modified PVDF membrane sustained stable Cassie states through homogeneous superhydrophilicity (water contact angle: 25.5 ± 1.4°) and continuous hydration layers, achieving complete flux recovery (100%) via combined deionized water rinsing and ultrasonic cleaning. These findings elucidate the critical role of substrate-driven interfacial engineering in the development of robust antifouling membranes for oil/water separation applications.