Effects of dilution and symmetry on concentrated ionic solutions

The place where two or more different materials meet each other is known as an interface. Interfaces are a part of everyday life. These interfaces can form between materials of the same phase (solid-solid, liquid-liquid) or between different phases (solid-liquid, solid-gas, liquid-gas). The molecules present at the interface between materials can behave very differently from the molecules in the rest of the material. It is therefore crucial to understand the different ways interfaces behave so that we may use that information to make new materials that can be used in a wide variety of applications like as electrolytes in better batteries, lubricants in extreme environments, and next generation drug delivery systems.

The work presented in this dissertation is focused on gaining a better understanding of how molecules behave at interfaces. Most of the work presented here is focused on a special group of chemicals called ionic liquids (ILs). ILs are liquid salts. They contain both positive and negative ions, but unlike common salts such as sodium chloride (table salt), ILs are liquid at room temperature. This gives them several useful properties, such as being non-flammable, conducting current, and not evaporating. The interfaces formed by ILs are unique in that the molecules form ordered structures along the interface. These structures are more ordered and larger than structures formed by traditional liquids. The aim of the research presented here is to determine what it is about ILs that gives them the ability to form these ordered structures, how those structures change when the ILs are mixed with other chemicals, and how scientists can control the composition of ILs to tune their behavior.

Future work on this subject might involve designing ionic liquids with specific tasks in mind such as increasing the amount of electricity they conduct to make higher capacity batteries or changing their viscosity to make high temperature lubricants.