Ionic liquids are organic salts with room temperature melting points. Their unique physicochemical properties make them popular choices in the fields of tribology, energy storage and production, and extractions. Previous studies show that IL’s interfacial volume, extending some nanometers from an adjacent surface, is characterized by the self-assembly of IL molecules into ordered structures. This ordering imparts unique properties which often govern the properties of ILs and affect their application in the aforementioned areas. This thesis describes research conducted to understand the behaviors and interactions of ILs at interfaces, along with investigations of bulk IL structures and transitions in the presence of water. The findings reported will help the scientific community by giving insight into the physical and chemical processes surrounding IL behavior, allowing ILs’ physicochemical properties to be more accurately tailored, via judicious synthesis, to a desired application.
Major findings of this work show that the ordered interfacial region may extend up to two orders of magnitude further from the interface than previously thought. Specifically, this thesis shows several examples of reversible IL self-assembly into long-range ordered films that extend up to ~ 2 μm from a surface. This is approximately twelve times the thickness of interfacial region previously reported.
Temperature controlled studies on the bulk structure of an IL at its phase transition temperatures aid in understanding the structural arrangement of molecules in the bulk fluid as a function of temperature. Spectroscopic analyses of these bulk studies and the above interfacial systems showed no similarities, indicating that the self-assembled interfacial structures are, in fact, unique.
Being hygroscopic in nature, water is the most common impurity found in ILs. Water can affect IL intermolecular forces and the resulting structures in bulk fluids as well as at the interface. One of the chapter of this thesis describes these interactions, and the variably hydrated IL structures for two classes of ILs via spectroscopic and electrochemical techniques.
The outcomes of this thesis will aid the community in understanding interfacial and bulk structures of ILs, as well as influences of temperature and water on these structures. The description of extended IL structures provides valuable insights into new design principles for truly task-specific ILs.