Abstract
Recent dielectric relaxation measurements on ionic liquids have shown that the dielectric response reflects a solution structure that is dominated by aggregates of ions. Despite the presence of some quite strongly polarised molecules, the dielectric constants measured for ionic liquids such as [emim]BF4 and mppy[dca] lies in the region of 10-15; this also reflects the degree of aggregation in the liquid and the limited degree of individual mobility possessed by each ion. This paper will discuss these recent results and their implications and correlate then with quantum mechanical calculations of the structure of the ions.