Directional oil retention and abrasion properties of microgrooved self-cleaning slippery surfaces for sanitation applications

Abstract

Lubricant infused slippery surfaces are vulnerable to external shear flow of fluids (water, air). This study reports the influence of mimicked commode flushing turbulent (Re ∼ 6129) water flow on the silicone oil retention and feces self-cleaning properties in microgrooved polydimethylsiloxane replicas fabricated using banana leaf template. Oil retention amounts are 28 %, 42 %, and 24 % for 20 min of constant turbulent flow in parallel (∥), perpendicular (⊥) directions to grooves and on untextured surfaces, respectively. Post flow, water slide-off angles (SAs) are ∼ 9° for ⊥ flow, ∼14° for ∥ flow, showcasing the retention of slipperiness. On the other hand, untextured surfaces lost their slipperiness. Also, oil retention in air under 200 gliding water droplets shows trend of ⊥ to grooves > ∥ to grooves > untextured. Furthermore, oil coated microgrooves displayed smaller coefficient of friction of 0.35 ± 0.009 (⊥ to grooves), 0.38 ± 0.003 (∥ to grooves), as compared to untextured surfaces (1.73 ± 0.198), when abraded with a steel ball in reciprocating motion using 1 N load, 40 mm⋅s⁻¹ sliding speed and 10 mm sliding distance. After 30 consecutive cycles of synthetic feces deposition, its residual amount is lowest when sliding on ∥ to grooves as compared to ⊥ to grooves and untextured surfaces. Clearly, a trade-off between ⊥ and ∥ directions to grooves can provide optimal oil retention and self-cleaning properties in sanitation and sewage systems.