The effects of subphase salt conditions on the interfacial behavior of a triblock copolymer poly(n-butyl acrylate)-poly(N-isopropylacrylamide)-poly(2-(dimethylamino)ethyl acrylate) (PnBA-PNIPAM-PDMAEA) were studied by the Langmuir monolayer technique and atomic force microscopy. Under acidic conditions, at the low ionic strength of NaCl solution (0.15 mol/L), the monolayer isotherm of the copolymer appears at large mean molecular areas (mmA) due to the destruction of the hydration of tertiary amine groups in PDMAEA blocks; At its middle and high ionic strengths (0.30 and 0.60 mol/L), the isotherms are close to that without salt due to the interfacial shrink of PDMAEA blocks resulted from their complete electrostatic shielding. Increasing the ionic strength of Na2SO4 solutions, the isotherms move to larger mmA. Under alkaline conditions, the interfacial stretching degrees of hydrophilic blocks increase with the concentrations of Na2SO4, NaSCN, and NaNO3 solutions (0.10-1.00 mol/L). Under different salt conditions, the Langmuir-Blodgett films of the copolymer exhibit separated circular micelles. Moreover, the so-called core-corona micelle structure can be core-shell-corona structure in strict meaning, which is first proposed in amphiphilic block copolymer systems at interfaces.

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Article address: https://doi.org/10.1021/acs.langmuir.5c00922