Green plasma engineering of cellulose surfaces for superhydrophobicity and tunable adhesion

This study investigates the modification of cellulose wettability through sequential plasma etching and film deposition to achieve superhydrophobic surfaces with tunable adhesion. The plasma treatment is a clean, solvent-free method that eliminates the need for hazardous chemicals, aligning with sustainable material development. Kraft cellulose samples were etched with oxygen plasma to generate nanoscale surface features and subsequently coated with hexamethyldisiloxane (HMDSO) films via plasma-enhanced chemical vapor deposition (PECVD). The effects of etching time and film thickness on surface properties were evaluated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), infrared reflection absorption spectroscopy (IRRAS), profilometry, and contact angle measurements. Oxygen plasma etching significantly altered the cellulose microstructure by increasing roughness and producing nanostructures. HMDSO deposition further modified surface chemistry, yielding water contact angles of ∼150° and diiodomethane contact angles of ∼120°. Among the tested conditions, the 144 nm HMDSO film showed optimal performance, preserving the nano-textured morphology and maintaining a stable superhydrophobic state over the aging period evaluated (45 days), with a contact angle hysteresis of ∼9° and a sliding (roll-off) angle of ∼7°. The combination of etching times (0–60 min) and HMDSO film thicknesses (144–910 nm) generated a broad range of adhesion levels — from pinned droplets that did not roll off even at 90° tilt to very low-adhesion surfaces — demonstrating highly tunable interfacial behavior. Overall, the integration of oxygen plasma etching and HMDSO film deposition provided an effective and environmentally friendly strategy for engineering cellulose surfaces. These modified surfaces have potential applications in self-cleaning materials, antifouling coatings, and lab-on-paper devices, highlighting the promise of plasma-based technologies for advancing functional cellulose-based materials with adaptable adhesion properties.