Buoyancy-controlled self-assembly and wettability of carbon nanocoatings evidenced by sounding rocket microgravity experiments

Evaporation-driven droplet deposition is central to printing and coating technologies, where capillary, Marangoni and buoyancy-driven flows govern particle organization and surface functionality. While buoyancy significantly affects internal convection under terrestrial conditions, its impact on the morphology and wettability of nanostructured coatings remains unclear. Here, we investigate gravity-dependent evaporation-assisted deposition of carbon nanomaterials using microgravity experiments performed within the ARLES campaign aboard the MASER 14 rocket, supported by the European Space Agency. Sessile droplets of HFE-7100 containing carbon nanotubes (CNTs), graphene flakes, or a 50/50 CNT–graphene mixture were sequentially deposited on silicon substrates under microgravity and reference 1 g conditions. Coatings obtained after up to four depositions were characterized by scanning electron microscopy and static water contact angle measurements. Microgravity markedly altered particle organization and pore structure. CNT coatings formed denser packings with smaller pores, resulting in increased hydrophobicity compared to 1 g samples. In contrast, graphene coatings exhibited greater roughness under microgravity and reduced contact angles. Mixed coatings showed gravity-dependent phase organization, yielding intermediate wettability in microgravity and graphene-dominated behavior at 1 g. These findings demonstrate that buoyancy-driven flow during evaporation controls nanoscale assembly and macroscopic wettability, highlighting microgravity as a platform for tailoring functional nanostructured coatings.