The Unique Simultaneously Oleophobic/Hydrophilic Behavior of a Nanometer-Thick Ionic Liquid on the Silica Surface

The unique simultaneously oleophobic/hydrophilic behavior of a nanometer-thick ionic liquid on the silica surface

Victor Manrique and Lei Li

Department of Chemical & Petroleum Engineering

University of Pittsburgh

Pittsburgh, PA 15261

Ionic liquids (ILs) have attracted extensive interests due to their exceptional physicochemical properties in the past two decades. Many promising applications of ILs, e.g., catalysis, electrochemistry, energy storage and lubrication, involve IL-solid interface. Therefore, it is critical to understand the molecular-level structure of ILs at the IL/solid interface. Previously, it has been demonstrated that contact angle testing is an effective approach to uncover the conformation of nanometer-thick films on the solid substrate. In the current study, nanometer-thick ionic liquid has been dip-coated on the silica substrate. Contact angles tests showed that IL/silica sample has unique simultaneously oleophobic/hydrophilic behavior. Based on ellipsometry, AFM and XPS characterizations, the molecular-level conformation of ILs has been determined. The effect of the chemical structure of both ILs and solid substrates has been discussed.