Direct measurements of ionic liquid layering at a single mica-liquid interface and in nano-films between two mica-liquid interfaces.

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Griffin, Lucy R 
Browning, Kathryn L 
Clarke, Stuart M 
Smith, Alexander M 
Perkin, Susan 

The layering of ionic liquids close to flat, charged interfaces has been identified previously through theoretical and some experimental measurements. Here we present evidence for oscillations in ion density ('layering') in a long chain ionic liquid (1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) near the interface with mica using two complementary approaches. Neutron reflection at the ionic liquid-mica interface is used to detect structure at a single interface, and surface force balance (SFB) measurements carried out with the same ionic liquid reveal oscillatory density in the liquid confined between two mica sheets. Our findings imply the interfacial structure is not induced by confinement alone. Structural forces between two mica surfaces extend to approximately twice the distance of the density oscillations measured at a single interface and have similar period in both cases.

0306 Physical Chemistry (incl. Structural)
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Phys Chem Chem Phys
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Royal Society of Chemistry (RSC)
We thank BP for funding (KLB and LRG), the EPSRC for a Doctoral Prize (AMS), and the John Fell Fund (Oxford University) for financial support. SP and AMS are grateful for support from the ERC under grant 676861: LIQUISWITCH.