Interactions between polyoxyethylene/polyoxypropylene/polyoxyethylene block copolymers and ionic surfactants

The interaction between polyoxyethylene/polyoxypropylene/polyoxyethylene, POE/POP/POE block copolymers (EO78PO30EO78, EO103PO39EO103, and EO32PO56EO32) and ionic surfactants (cationic, tetradecyltrimethylammonium bromide, C(14)TABr, and anionic, sodium dodecyl sulphate, SDS) in water was studied by conductance, surface tension, dye solubilization, dye spectral change and viscosity measurements. The results from different techniques suggested that all the three copolymers interact strongly with the anionic surfactant SDS but not with the cationic surfactant C(14)TABr. This is quite clear from the two transitions observed for the polymer-anionic surfactant systems, one below and one above the critical micelle concentration (c.m.c.) of the surfactant and from the fact that only one break point corresponding to the c.m.c. of the surfactant is observed in the polymer-cationic surfactant systems. in the case of polymers interacting with the anionic surfactant, the two transitions indicate the beginning and completion of polymer surfactant interaction. Viscometric results showed the formation of polyelectrolyte complexes. The influence of the molecular characteristics of the block copolymers, type of the surfactant and temperature on the interaction is described.