Non-toxic self-cleaning large area cement blocks fabrication by biomimicking superhydrophobic periwinkle flowers

Self-cleaning superhydrophobic cement based surfaces are predominantly fabricated by functionalization of either superhydrophilic micro/nano powders or their structural components with toxic chemicals (alkylsilanes, perfluoropolyethers). In this article, a non-toxic, scalable and cost-effective fabrication colloidal lithography approach is reported to prepare superhydrophobic cement surfaces. This study will firstly report the discovery of superhydrophobicity in Periwinkle flowers, followed by biomimicking their surface micro-conical textures on the polydimethylsiloxane (PDMS) and cement surfaces. The protruding micro-cones possess average height of 15 ± 2 µm, bottom diameter of 12 ± 2 µm and pitch of 20 ± 4 µm. The Wenzel roughness of the petals measured by a 3D non-contact optical profilometer is 2.3 ± 0.12. The water static contact angle (SCA) on the petals is 148 ± 2°, roll-off angle (RA) is 13 ± 1° and contact angle hysteresis (CAH) is 12 ± 3° demonstrating quasi-superhydrophobicity. A key highlight is the development of textured cement and PDMS surfaces of up to 152 cm2 areas starting from 2.25 cm2 areas of petals, i.e. achieving ∼ 68 times bigger areas as compared to that of the master templates. The textured PDMS surfaces exhibited superhydrophobicity displaying SCA of 156 ± 2°, CAH of 9 + 1° and RA of 10 ± 1°, while the textured cement surfaces exhibited a transition from superhydrophilicity to quasi- superhydrophobicity with SCA of 147 ± 2°, CAH of 16 + 3° and RA of 17 ± 3°. The rolling water droplets took away the mud particles demonstrating self-cleaning ability. This study showcases an environmentally sustainable solution to prevent water leakages in the cement-based constructions and can be easily adapted by the non-specialist users.