Effect of Airborne Hydrocarbons on the Wettability of Phase Change Nanoparticle Decorated Surfaces.

We present here a detailed study of the wettability of surfaces nanostructured with amorphous and crystalline nanoparticles (NPs) derived from the phase-change material Ge ₂ Sb ₂ Te ₅ (GST). Particular attention was devoted to the effect of airborne surface hydrocarbons on surface wetting. Our analysis illustrates that a reversible hydrophilic-hydrophobic wettability switch is revealed by combined ultraviolet-ozone (UV-O ₃ ) treatments and exposure to hydrocarbon atmospheres. Indeed, the as-prepared surfaces exhibited a hydrophilic state after thermal annealing or UV-O ₃ treatment which can partially remove hydrocarbon contaminants, while a hydrophobic state was realized after exposure to hydrocarbon atmosphere. Using high-angle annular dark-field scanning transmission electron microscopy for the specially designed GST NP decorated graphene substrates, a network of hydrocarbon connecting GST NPs was observed. Our findings indicate that airborne hydrocarbons can significantly enhance the hydrophobicity of nanostructured surfaces. Finally, the experiments reveal that previously defined hydrophilic materials can be used for the design of hydrophobic surfaces even if the meniscus is highly adhered to a solid surface, which is in agreement with our qualitative model involving the contribution of the nanomeniscus formed between the substrate and a decorating NP.