The association behavior of poly(ethylene oxide)-polypropylene oxide)-polyethylene oxide) (PEO-PPO-PEO) block copolymers in aqueous solution with hexadecyltrimethylammonium bromide (HTAB), tetradecyltrimethylammonium bromide (TTAB), and dimethylene bis(decyldimethylammonium bromide) (10-2-10), was studied by fluorescence, viscosity, and Krafft temperature measurements. It has been observed that (EO)(18)(PO)(31)(EO)(18) interacts more strongly than (EO)(2)(PO)(15.5)(EO)(2) and (EO)(2.5)(PO)(31)(EO)(2.5) with HTAB/TTAB due to synergistic interactions. A stronger capability of (EO)(18)(PO)(31)(EO)(18) to interact with cationic surfactants arises from the greater number of electronegative EO units (total 36 EO units) than of (EO)(2)(PO)(15.5)(EO)(2) (total 4 EO units) and (EO)(2.5)(PO)(31)(EO)(2.5) (total 5 EO units). The antagonistic mixing behavior of present triblock polymers has been observed with 10-2-10. A difference in the mixing behavior of the latter from that of HTAB/TTAB has been attributed to its dimeric nature, which may create steric hindrances with triblock polymer components at the head group region in the mixed state. (C) 2004 Elsevier Inc. All rights reserved.