Structural and Dynamical Properties of Liquid and Solid Phases of Ionic Liquids Confined Inside Nanoporous Materials

• Main Author: Singh, Ramesh
• Other Authors: Clayton, Geoff
• Format: Others
• Language: en
• Published: LSU 2012
• Subjects: Chemical Engineering
• Online Access: http://etd.lsu.edu/docs/available/etd-04262012-113406/

The purpose of this research is to investigate the physical properties of ionic liquids (ILs) confined inside nanopores of different materials and morphologies. We are interested to study the effect of pore material, morphology and addition of organic solvents on the properties of confined ILs. Understanding the behavior of ILs inside nanopores is relevant to potential applications of these systems in electrochemical double layer capacitors (EDLCs) and dye sensitized solar cells (DSSCs). Such a fundamental understanding is also crucial to optimize the synthesis of hard-templated 1D nanostructures (nanorods, nanotubes, nanowires) based on organic salts, which may be imparted properties (e.g., magnetic, optical) that are desirable for different applications (magnetic hyperthermia cancer treatment, medical imaging, sensors). In this work we have used molecular dynamics (MD) simulations to investigate systems of representative ILs, [BMIM+][PF6-] and [EMIM+][TFMSI-], inside several model materials (e.g., slit-shaped graphitic and titania pores, carbon nanotubes). Formation of different layers of ions was observed for the confined ILs irrespective of variations in pore size, shape, material and amount of solvent. In all cases, change in pore loading leads to lower densities of ions in the center of the pore. The cations close to the pore walls tend to align with their imidazolium rings parallel to the pore surface in the case of carbon materials, and multiple preferential orientations are observed in the case of titania pores. For all porous materials studied, the dynamics of the ions depend strongly on their location with respect to the surface; bulk-like dynamics are generally observed for the ions in the center regions of the pore, with the dynamics becoming slower as the ions get closer to the pore surfaces. Addition of acetonitrile solvent also shows similar layering behavior for ILs and solvent near the pore wall with less variation in the center of the pore. Preferential orientations of the ions remain unaffected and solvent molecules tend to align flat near the pore surface. The dynamics of the ions and molecules increases linearly with increase in IL molar concentration both near the wall and in the center of the pore.