Self-assembly of cations in aqueous solutions of 1-alkyl,3-decylimidazolium bromide (with four different alkyl chains, methyl, butyl, heptyl, and decyl chain,) have been studied using atomistic molecular dynamics simulations. Polydisperse aggregates of cations are formed in the solution with alkyl tails in the core and the polar head groups present at the surface of the aggregates. The shape of the aggregates is dictated by the length of the alkyl chain. Aggregation numbers increase steadily with the increasing alkyl chain length. The greater asymmetry in the two-substituent chain length leads to a different surface structure compared to that of the cations with alkyl chains of similar length.