  Here we present a theory of ion aggregation and gelation of room temperature
ionic liquids (RTILs). Based on it, we investigate the effect of ion
aggregation on correlated ion transport - ionic conductivity and transference
numbers - obtaining closed-form expressions for these quantities.The theory
depends on the maximum number of associations a cation and anion can form, and
the strength of their association. To validate the presented theory, we perform
molecular dynamics simulations on several RTILs, and a range of temperatures
for one RTIL. The simulations indicate the formation of large clusters, even
percolating through the system under certain circumstances, thus forming a gel,
with the theory accurately describing the obtained cluster distributions in all
cases. We discuss the possibility of observing a gel phase in neat RTILs, which
has hitherto not been discussed in any detail.
