Identifier

etd-06232011-114118

Degree

Master of Science (MS)

Department

Chemical Engineering

Document Type

Thesis

Abstract

Molecular dynamics simulations were performed to investigate the structural and dynamical properties of ionic liquid (IL) [EMIM+][TFMSI-] confined inside slit-like graphite pores. ILs are salts composed of an organic cation and an organic or inorganic anion with melting point below 100ºC. Their unique properties such as great thermal and chemical stability have gained them immense attention in recent years. The main goal of this research is to understand how molecular level properties of ILs are affected by the properties of the nanoporous materials. The results obtained in this work indicate that pore size has a profound effect on structural and dynamical properties of ILs. Significant layering was observed at the IL-graphite interface, with the number of layers of cations and anions showing a monotonic dependence with pore size. Radial distribution function shows that the liquid structure of the confined IL is similar to that observed in bulk systems. Strong interaction was observed between oxygen atom of anion and acidic hydrogen atom of cation ring, suggesting formation of weak hydrogen bonding between cations and anions. Both cations and anions lie flat near the pore walls. It was observed that dynamics of cations and anions increase with increases in pore size. The results also suggest that cations diffuse faster than anions irrespective of pore size. The results for means square displacement (MSD) show three different regimes characterized by different time dependences (1) Ballistic (2) diffusive (3) sub-diffusive. It was observed that dynamics of cations and anions in the regions close to the surface are slower as compared to the liquid in the center. Single particle dynamics was studied by finding van Hove self correlation function (VHSCF) and self intermediate scattering function (SISF). At short time, the ions do not interact much with the neighboring ions. The intermediate regime in which ions rattle inside the cage MSD increases slowly with time. For long-time motion when particle escape from the cage, the ions are in vii diffusive and MSD shows a linear relation with time. The results of SISF as a function of wave vector indicate that relaxation time decreases with increase in wave vector.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hung, Francisco R.

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