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AFM Study of Liquid Nanomenisci and Wetting of Partially Supported Graphene Monolayers
The recent development of nanofluidics raises many questions about hydrodynamics and wetting at nanometer scale. I will present two experiments developed in CEMES to address these issues. I will show that that advanced FM-AFM techniques are promising tools for the investigation of mechanical properties of nanomenisci. Using non conventional AFM tips with a nanofiber at their extremity, we investigate the conservative and dissipative contributions to the tip-liquid interaction. The dissipation and added mass effects in the viscous layer around the oscillating nanofiber were measured and compared to a theoretical model, showing interesting features inherent to the cylindrical geometry of the system. The effective spring constant of the oscillated meniscus was also determined experimentally for unbounded and confined interfaces. This technique opens the way to a systematic study of the dissipation at a moving contact line which is an open question in wetting science. Recently, the wetting properties of supported graphene monolayers were the subject of intense research scrutiny owing to the potential applications of graphene as a coating material. A fundamental and yet unresolved issue is how the one-atom thick graphene layer influences the wettability of the underlying substrate. By its well-defined chemical and geometrical properties, supported graphene therefore provides a model system to disentangle the respective roles of short and long range interactions on the shape of liquid droplets. I will present an experimental study of the wetting properties of graphene monolayers partially supported by nanotextured silicon substrates, an original system which allows quantitative measurements of the effect of the underlying substrate.