Surface free energy and wettability of bio-inspired water repellent surfaces mimicked from nature

Surface free energy of artificial surfaces mimicked from nature, which attributes the liquid-solid interfacial interaction has been a major area of interest in fundamental and biomimetic research. In the present work, polymeric surfaces were fabricated by two-step templating from Bauhinia purpurea (Orchid Tree), Alocasiaodora (Elephant ear yam), Cocos nucifera (Coconut), Borassus flabellifer (Palm leaves), Colocasiaesculenta (Taro), and Catharanthus roseus (Periwinkle) leaf surfaces with various wettabilities. The negative molds of Polydimethylsiloxane (PDMS) were obtained in the first-step and the final mimicked surfaces of Polyethylene terephthalate (PET) and Epoxy resin were obtained in the second-step templating. The microstructures on the surfaces were confirmed by taking images in micrometer scale. Among the number of methods, Owens- Wendt model was chosen to calculate the surface energies of the fabricated surfaces. A series of binary mixtures of water-dimethyl sulfoxide (DMSO) system were taken and Owens Wendt parameters including dispersive surface energy and polar surface energy were established. Contact angles of the binary mixtures with different mole fractions on all the solid surfaces were measured and the obtained data were fitted into Owens Wendt model. The dispersive and polar surface energies of all the solid surfaces were obtained from the slop of the Owens-Wendt plots. The total surface energies and work of adhesion of the solid surfaces were calculated and a correlation with the microstructures were made to attribute the reasoning of wettability. The measurement of contact angles of liquid mixtures is a simple approach for determining surface energy of a solid surface, which facilitates the biomimetic fabrication of surfaces with various wettabilities from nature. Through this study knowing the wettability requirement with surface energy & microstructure, any specific surface with specific wettability can be prepared.

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