Clouding and aggregation behavior of PEO/PPO/PEO and PPO/PEO/PPO block copolymers in aqueous solution

Aqueous solutions of four ethylene oxide-propylene oxide block copolymers [L43 (EO 6 PO 21 EO 6 ), L62 (EO 5 PO 30 EO 5 ), 17R4 (PO 14 EO 24 PO 14 ) and 25R4 (PO 19 EO 33 PO 19 )] in the presence of ionic surfactants, viz. sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (C 16 TABr), and sodium chloride were examined by cloud point, surface tension and dynamic light scattering techniques. Results suggest that all the four copolymers interact strongly with SDS (anionic surfactant) but more weakly with C 16 TABr (cationic surfactant). The surfactants produce a marked increase in the cloud point of the block copolymer solutions; the CP-increasing effect is more pronounced for SDS. Increasing the nonpolar chain of the surfactant favors the increase in CP. When ionic surfactants are present, an increase in the cloud point is due to the formation of mixed micelles. However, the CP of these copolymers decreased in the presence of NaCl. High SDS or C 16 TABr concentration is required to increase the CP in the presence of salt solution. Surface tension/ dynamic light scattering data reveal that the copolymer-surfactant system behaves like a charged polyelectrolyte with a stronger solubilizing action.