Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Poster: Interfaces and Thin Films (joint session with DECHEMA and VDI)

CPP 9.32: Poster

Monday, March 11, 2013, 17:30–19:30, Poster C

Diffusion and demixing dynamics of water and ethanol in a self-adjusting molecularly thin slit-pore — •Nikolai Severin, Igor M. Sokolov, and Jürgen P. Rabe — Department of Physics, Humboldt-Universität zu Berlin Newtonstr. 15, 12489 Berlin, Germany

The behaviour of multicomponent liquids in confining geometries is a fundamental physical problem, which plays a central role in fields such as nano-fluidics, molecular biophysics, single molecule spectroscopy, and nano-chemistry, e.g. for molecular transport through channels of biological membranes, analyte recognition in molecular assays, and molecular synthesis. We followed with nanometer-scale lateral resolution the in-situ dynamics within mixed monomolecular water-ethanol films in a slit pore between mica and graphene, employing scanning force microscopy to image the graphene topography conforming to the film. Water and ethanol, highly miscible in three dimensions are shown to nano-phase separate in monolayers within the pore, consisting of a hydrophilic atomically flat mica surface and a more hydrophobic graphene layer. Graphene conforms to the liquid film, bending at the boundaries between the domains of water and ethanol to accommodate their different thicknesses of 80±20 pm. The growth dynamics of the domains allows to determine a lower bound for the two-dimensional diffusion constant of ethanol in water of D ≥ 2 x 10s⁻¹⁴ ms²s⁻¹.