title: Wetting and evaporative aggregation of nanofluid droplets on CVD-synthesized hydrophobic graphene surfaces.
abstract: The wetting and evaporative aggregation of alumina nanofluids (Al2O3) are examined for CVD-synthesized graphene-coated (GC) surfaces that are known as strongly hydrophobic (θcontact ≈ 90°). Our findings are compared to those associated with a hydrophilic cover glass (CG) substrate (θcontact ≈ 45°). The nanofluidic self-assemblies on the GC substrate are elaborately characterized in terms of the droplet wetting/crack formation, the particle migration time over the evaporative time (CR), the Derjaguin-Landau-Verwey-Overbeek forces (FDLVO), and the relative thermal conductivity (KR). The GC substrate forms relatively thicker and larger cracks and requires a longer evaporation time. Both the GC and CG substrates share approximately the same time constant CR, which suggests the formation of coffee-ring patterns for both substrates. The GC shows negative FDLVO, which implies a repulsive force between the nanoparticles and the substrate, and the CG shows a positive FDLVO of attraction. Furthermore, a more than 3 order of magnitude larger thermal conductivity of GC compared to that of CG drives significantly different particle/fluid motions near the drop edge areas between the two substrates.
authors.affiliation: School of Mechanical and Aerospace Engineering, Seoul National University , Gwanak-gu, Seoul 151-742, South Korea.
authors.forename: Jae S
authors.initials: JS
authors.lastname: Park
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Kihm
authors.forename: Honggoo
authors.initials: H
authors.lastname: Kim
authors.forename: Gyumin
authors.initials: G
authors.lastname: Lim
authors.forename: Sosan
authors.initials: S
authors.lastname: Cheon
authors.forename: Joon S
authors.initials: JS
authors.lastname: Lee