(180bd) Molecular Dynamics Simulations of Nanoparticle Interactions with Ionic Liquids

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.

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.