Binding of tetradecyltrimethylammonium bromide to the ABA block copolymer Pluronic F127 (EO₉₇PO₆₉EO₉₇): Electromotive force, microcalorimetry, and light scattering studies

The interaction between the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the Pluronic triblock copolymer F127 was investigated. F127 is a nonionic surfactant with structural formula EO97PO69EO97, where EO represents the ethylene oxide block and PO represents the propylene oxide block. A combination of experiments involving a TTAB selective electrode (electromotive force), isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), and light scattering have shown that TTAB binds to both monomeric and micellar F127. TTAB forms a polymer/micellar TTAB complex with monomeric F127. In addition, TTAB binds to F127 micelles leading to the transformation of the aggregated F127 into mixed micelles followed by a breakdown of these aggregates into smaller mixed F127/TTAB aggregates as more TTAB is added. This process continues until all the aggregated F127 is dissociated. DSC measurements have also shown that small amounts of TTAB (typically 10-4 mol dm-3) can decrease the critical micelle temperature (cmt) of F127. This represents a third mode of binding in which TTAB induces F127 to form micelles at temperatures several degrees below its "pure" cmt. Possible mechanisms for these processes involving different modes of interaction of TTAB with F127 are introduced and discussed