title: Hydraulic transport across hydrophilic and hydrophobic nanopores: Flow experiments with water and n-hexane.
abstract: We experimentally explore pressure-driven flow of water and n-hexane across nanoporous silica (Vycor glass monoliths with 7- or 10-nm pore diameters, respectively) as a function of temperature and surface functionalization (native and silanized glass surfaces). Hydraulic flow rates are measured by applying hydrostatic pressures via inert gases (argon and helium, pressurized up to 70 bar) on the upstream side in a capacitor-based membrane permeability setup. For the native, hydrophilic silica walls, the measured hydraulic permeabilities can be quantitatively accounted for by bulk fluidity provided we assume a sticking boundary layer, i.e., a negative velocity slip length of molecular dimensions. The thickness of this boundary layer is discussed with regard to previous capillarity-driven flow experiments (spontaneous imbibition) and with regard to velocity slippage at the pore walls resulting from dissolved gas. Water flow across the silanized, hydrophobic nanopores is blocked up to a hydrostatic pressure of at least 70 bar. The absence of a sticking boundary layer quantitatively accounts for an enhanced n-hexane permeability in the hydrophobic compared to the hydrophilic nanopores.
authors: Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany and Sorption and Permeation Laboratory, BASF SE, D-67056 Ludwigshafen, Germany.
authors: Simon
authors: S
authors: Gruener
authors: Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany and Department Sample Environments, Helmholtz-Centre Berlin for Energy and Materials, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors: Dirk
authors: D
authors: Wallacher
authors: Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany.
authors: Stefanie
authors: S
authors: Greulich
authors: Institute of Materials Physics and Technology, Eißendorfer Str. 42, D-21073 Hamburg-Harburg, Germany.
authors: Mark
authors: M
authors: Busch
authors: Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany and Institute of Materials Physics and Technology, Eißendorfer Str. 42, D-21073 Hamburg-Harburg, Germany.
authors: Patrick
authors: P
authors: Huber
mesh_terms: D001128:Argon / Q000737:chemistry; D002138:Calibration; D005740:Gases / Q000737:chemistry; D005898:Glass / Q000737:chemistry*; D006371:Helium / Q000737:chemistry; D006586:Hexanes / Q000737:chemistry*; D057446:Hydrodynamics; D057927:Hydrophobic and Hydrophilic Interactions; D044085:Microfluidics; D008962:Models, Theoretical; D009038:Motion; D058608:Nanopores; D010539:Permeability; D011312:Pressure; D012822:Silicon Dioxide / Q000737:chemistry*; D012995:Solubility; D013499:Surface Properties; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry*
chemical_list: D005740:Gases; D006586:Hexanes; D014867:Water; D006371:Helium; C026385:n-hexane; D001128:Argon; D012822:Silicon Dioxide