Under confinement : molecular dynamics investigations of ions and molecules in nanopores and at nanoscale interfaces.

The behavior of molecules in nanopores and at nanoscale interfaces are of fundamental importance in chemical applications such as electrical energy storage and water desalination. Investigations into carbon based structures such as carbon nanotubes and graphene sheets with confined fluids are promising for the enhancement of such technologies. Through molecular dynamics simulations, investigations of aqueous electrolytes in a series of carbon nanotubes were performed, examining ionic current and solvent transport under an applied electric field. A departure from linearity in the correlation between current computed and applied potential was observed with pores comparable to solvated ion dimension, owing to significant energy penalties for ion entry. Ion density and solvation, along with the orientation of water molecules in charged and uncharged pristine nanotubes were also investigated. Carbon nanotubes having surface functionalization with hydrogen and hydroxyl groups were created to investigate the outcomes of surface modification on ion entry into pores. We discuss our ability to tune fluid structure in nanochannels with such surface charge modification, to control what ions traverse a pore and how to selectively trap them. Additionally, model supercapacitors consisting of graphene electrodes and ionic liquid electrolytes were also investigated with manipulation of ion constituents. We present findings on how to formulate binary ionic liquid mixtures to attain desired density, conductance, and electric double layer potential. This work provides significant contributions to the design of aqueous electrolytes, ionic liquids, and electrodes, and enhancement of nanoscale properties. The implications for water desalination and energy storage capabilities are profound.