Conductance (K), pyrene fluorescence (I-1/I-3), cloud point (C-P), and Krafft temperature (K-T) measurements have been carried out for various dimethylene bis(alkyldimethylammonium bromide) (gemini) surfactants with different poly(ethylene oxide)-poly(propylene oxide)poly(ethylene oxide) triblock polymers (TBP). From the K and I-1/I-3 Studies, the critical micelle concentrations of mixed micelle formation between the gemini and TBP have been determined using regular solution theory. It has been observed that mixed micelle formation in all the binary mixtures of gemini + TBP occurs due to the unfavorable mixing, the magnitude of which decreases with increased hydrophobicity of the gemini component. The results are further supported by evaluating the mean micelle aggregation number and enthalpy of fusion from fluorescence and Krafft temperature measurements, respectively. (c) 2004 Elsevier Inc. All rights reserved.