INTERACTION OF ABA BLOCK-COPOLYMERS WITH IONIC SURFACTANTS IN AQUEOUS-SOLUTION

Block copolymers of the type poly(ethylene oxide)-poly(propylene oxide )-poly(ethylene oxide) [EO(x)PO(y)E0(x)] form micelles with a hydropho bic core of propylene oxide and a palisade layer of the ethylene oxide . We studied the influence of sodium dodecyl sulfate (SDS) on the aggr egation behavior of F127 (EO(97)PO(69)OE(97)) by static and dynamic li ght scattering, electric birefringence, and calorimetric methods. We o bserved that for block copolymer solutions in the range of 1-5 % and i ncreasing concentration of SDS the light scattering passed through a d eep minimum, the electric birefringence passed over a maximum, and the endothermic peak of the DSC signals which is due to the micellization of the block copolymer disappeared. The results show that SDS binds t o monomers of F127 and thereby suppresses completely the formation of F127 micelles. At saturation about six molecules of SDS bind to one F1 27 molecule. The birefringence data indicate that the F127/SDS complex exists in a more or less extended conformation and not as a coil. The binding of SDS on F127 was also confirmed by surface tension measurem ents. These measurements show that the surface active block copolymers are replaced from the interfaces by SDS molecules. The binding of SDS on F127 begins at concentration far below the critical micelle concen tration of SDS.