Synthesis and Surface Functionalization of SnO₂ Nanoparticles and Their Superhydrophobic Coatings

Modulation of surface wettability is demonstrated using SnO₂ nanoparticles (NPs) upon surface functionalization. Quantum sized SnO₂ NPs synthesized by soft chemical route are annealed under ambient conditions at different temperatures to increase grain size as revealed by field emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. These NPs were treated in a cyclohexane medium with octadecyltrichlorosilane (OTS) to create an organic/inorganic interface. Atomic force microscopy reveals increased roughness of functionalized films with increasing size of SnO₂ NPs, whereas Raman studies illustrate ordered OTS molecules on SnO₂ surfaces forming a hetero-structure interface. Water contact angle measurements on spin coated plain SnO₂ NPs films show distinct hydrophilic nature with a contact angle (CA) of 15±2°. Creation of an interface with OTS with these films show hydrophobicity with a minimum contact angle of 137° for the quantum sized SnO₂ NPs. Surface wettability is further modulated by introducing enhanced surface roughness with increasing size of SnO₂ NPs and clusters in the OTS treated films. Super hydrophobicity (CA > 150°) is clearly demarcated after silanization of SnO₂ NPs of size of 12 nm and above. Within the frame work of Cassie-Baxter model, super hydrobhobicity is explained based on surface roughness and geometrical architectures.