Three gemini pyrrolidine-based ionic liquids, 1,1'-(butane-1,4-diyl)bis(1-alkylpyrrolidinium) bromide ([CnPY-4-C(n)py][Br-2], n = 10, 12, 14), were synthesized. Their aggregation behavior in aqueous solution was systematically investigated by surface tension, electrical conductivity, and steady-state fluorescence. Compared with their corresponding monomers, N-alkyl-N-methylpyrrolidinium bromide (CnMPB), [C(n)py-4-Cn(p)y] [Br-2], have higher surface activity. The special structure of [C(n)py-4-Cn(p)y] [Br-2], that has a spacer in their hydrophilic head groups results in a lower surface excess concentration (Gamma(max)) and a larger molecular cross-sectional area (A(min)). Electrical conductivity studies show a lower degree of counter-ion binding to the aggregates. A smaller aggregation number (N-agg) is observed by the pyrene fluorescence quenching method. A series of thermodynamic parameters (Delta G(agg)(0), Delta H-agg(0), -T Delta S-agg(0)) of aggregation derived from electrical conductivity indicate that the aggregation of [C(n)py-4-Cn(p)y] [Br-2], is enthalpy-driven, while aggregation of CnMPB is entropy-driven at low temperatures but enthalpy-driven at high temperatures. (C) 2012 Elsevier Inc. All rights reserved.