Influences of Subphase Salt Conditions on the Interfacial Behavior of Triblock Copolymer PnBA-PNIPAM-PDMAEA

The effects of subphase salt conditions on the interfacial behavior of a triblock copolymer, poly(<i>n</i>-butyl acrylate)-poly(<i>N</i>-isopropylacrylamide)-poly(2-(dimethylamino)ethyl acrylate) (PnBA-PNIPAM-PDMAEA), were studied by the Langmuir film balance 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 (mm<i>A</i>) due to the destruction of the hydration of tertiary amine groups in the 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 shrinkage of the PDMAEA blocks resulting from their complete electrostatic shielding. With increasing the ionic strength of Na₂SO₄ solutions, the isotherms move to larger mm<i>A</i> values. Under alkaline conditions, the interfacial stretching degrees of the 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 separate circular micelles. Moreover, the so-called core-corona micelle structure can be a core-shell-corona structure in strict meaning, which is first proposed in amphiphilic block copolymer systems at interfaces.