Classical hydrodynamic models predict that infinite work is required to move a three-phase contact line, defined here as the line where a liquid/vapor interface intersects a solid surface. Assuming a slip boundary condition, in which the liquid slides against the solid, such an unphysical prediction is avoided. In this article, we present the results of experiments in which a contact line moves and where slip is a dominating and controllable factor. Spherical cap-shaped polystyrene microdroplets, with nonequilibrium contact angle, are placed on solid self-assembled monolayer coatings from which they dewet. The relaxation is monitored using in situ atomic force microscopy. We find that slip has a strong influence on the droplet evolutions, both on the transient nonspherical shapes and contact line dynamics. The observations are in agreement with scaling analysis and boundary element numerical integration of the governing Stokes equations, including a Navier slip boundary condition.

The dielectrophoretic integration of single- and few-layered graphenes from three distinct graphene suspensions is presented, enabling the parallel assembly of individual two-dimensional nanostructures at predefined locations. The first suspension is an aqueous solution of graphene oxide, the second is ultrasonically exfoliated pristine graphene in N-methyl-pyrrolidone (NMP), and the third is exfoliated graphene in surfactant-stabilized 1 wt % aqueous SDBS solutions. The most crucial aspect for the successful thin flake deposition is the solution quality of the exfoliated graphene. After dielectrophoresis, single-layer graphene oxide is placed between the electrodes, which, while initially insulating, recovers its electrical conductivity following thermal reduction. From the chemically unmodified graphene-NMP solutions, the directed assembly of electrically active few-layer graphene flakes is realized, with flake thicknesses in the range 8–30 nm. Liquid phase exfoliation in water-surfactant solutions yields significantly thicker flake dimensions from 50 to several 100 nm due to the higher enthalpy of mixing in the dispersion. To achieve single-layer pristine graphene dielectrophoretic deposition, higher solution qualities must be available, consisting largely of single-layer graphene sheets. The reported research provides an important framework for parallel fabrication approaches of graphene-based devices.

No abstract

No abstract

No abstract