279478 Molecular Dynamics Simulations of Nanoparticle Interactions with Ionic Liquids

Monday, October 29, 2012
Hall B (Convention Center )
Michael Machas, Denzil S. Frost and Lenore L. Dai, School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ

Molecular Dynamics Simulations of Nanoparticle Interactions with Ionic Liquids

            Recently, a number of publications have suggested that ionic liquids (ILs) can absorb solid particles.  This development may have implications in fields like oil sand processing, oil spill beach cleanup, and water treatment.  In this paper we provide a computational investigation of this phenomenon via molecular dynamics simulations using nanoparticles.  Two particle surface chemistries are investigated: (1) hydrocarbon-saturated and (2) silanol-saturated.  Employing 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) as a model IL, these nanoparticles were allowed to equilibrate at the IL/water and IL/hexane interfaces to observe how they self-assembled at the interface.  At the IL/water interface, hydrocarbon-based nanoparticles were nearly completely absorbed by the IL, while the silica nanoparticles maintained equal volume in both phases.  At the IL/ hexane interface, the hydrocarbon nanoparticles maintained minimal interactions with the IL while the silica nanoparticles were nearly completely absorbed by it.  Studies of these two nanoparticles completely immersed in the IL indicate that the surface chemistry has a great affecting on the corresponding IL liquid structure.  These effects include layering of the ions, hydrogen bonding, and irreversible absorption of some ions to the silica nanoparticle surface.  We quantify these effects with respect to each nanoparticle.  The results suggest that ILs exhibit particle absorption capability because they can form pseudo-crystalline solvation layers around the particles.

Description: denzilfrost:Desktop:solvationlayer.png

Figure 1 [BMIM][PF6] solvation shells around a hydrocarbon nanoparticle (a) and a silica nanoparticle (b).  [BMIM] cations and [PF6] anions are illustrated in yellow and green, respectively.

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