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Ions Tune Interfacial Water Structure and Modulate Hydrophobic Interactions at Silica Surfaces
journal contribution
posted on 2020-04-01, 15:35 authored by Aashish Tuladhar, Shalaka Dewan, Simone Pezzotti, Flavio Siro Brigiano, Fabrizio Creazzo, Marie-Pierre Gaigeot, Eric BorguetThe structure and
ultrafast dynamics of the electric double layer
(EDL) are central to chemical reactivity and physical properties at
solid/aqueous interfaces. While the Gouy–Chapman–Stern
model is widely used to describe EDLs, it is solely based on the macroscopic
electrostatic attraction of electrolytes for the charged surfaces.
Structure and dynamics in the Stern layer are, however, more complex
because of competing effects due to the localized surface charge distribution,
surface–solvent–ion correlations, and the interfacial
hydrogen bonding environment. Here, we report combined time-resolved
vibrational sum frequency generation (TR-vSFG) spectroscopy with ab
initio DFT-based molecular dynamics simulations (AIMD/DFT-MD) to get
direct access to the molecular-level understanding of how ions change
the structure and dynamics of the EDL. We show that innersphere adsorbed
ions tune the hydrophobicity of the silica–aqueous interface
by shifting the structural makeup in the Stern layer from dominant
water–surface interactions to water–water interactions.
This drives an initially inhomogeneous interfacial water coordination
landscape observed at the neat interface toward a homogeneous, highly
interconnected in-plane 2D hydrogen bonding (2D-HB) network at the
ionic interface, reminiscent of the canonical, hydrophobic air–water
interface. This ion-induced transformation results in a characteristic
decrease of the vibrational lifetime (T1) of excited interfacial O–H stretching modes from T1 ∼ 600 fs to T1 ∼ 250 fs. Hence, we propose that the T1 determined by TR-vSFG in combination with DFT-MD simulations
can be widely used for a quantitative spectroscopic probe of the ion
kosmotropic/chaotropic effect at aqueous interfaces as well as of
the ion-induced surface hydrophobicity.
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dynamicab initio DFT-basedStern layerT 1DFT-MDinterfacewater coordination landscapesurface charge distributionin-plane 2 D hydrogenion-induced transformation resultsAIMDtime-resolved vibrational sum frequency generationEDLion-induced surface hydrophobicityIons Tune Interfacial Water StructureD-HBModulate Hydrophobic Interactions
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