Interaction between cationic, anionic, and non-ionic surfactants with ABA block copolymer Pluronic PE6200 and with BAB reverse block copolymer Pluronic 25R4

The interaction in aqueous solution between either the normal block copolymer poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide): Pluronic PE6200 [(EO)₁₁–(PO)₂₈–(EO)₁₁], or the reverse block copolymer poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide): Pluronic 25R4 [(PO)₁₉–(EO)₃₃–(PO)₁₉] and the surfactants sodium decylsulfate, C₁₀OS, decyltrimethyl ammonium bromide, C₁₀TAB, and pentaethylene glycol monodecyl ether, C₁₀E₅, was investigated and the aggregation behavior of these surfactants with Pluronics was compared. Surface tension measurements show that Pluronics in their non-aggregated state better interact with the anionic surfactant C₁₀OS than with cationic and non-ionic ones. The presence of the two Pluronics induces the same lowering of the aggregation number of C₁₀OS as shown by fluorescence quenching measurements. The number of polymer chains necessary to bind each C₁₀OS aggregate has been estimated to be 6 for PE6200 and 2 for 25R4. Furthermore, this surfactant also induces the same increment in the gyration radius of the polymers as revealed by viscosimetry. Calorimetric results have been reasonably reproduced by applying a simple equilibrium model to the aggregation processes.