Hydrogen-Bonding-Driven Complexation of Polystyrene-block-poly(ethylene oxide) Micelles with Poly(acrylic acid)

Hydrogen-bonding complexation between spherical diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) micellcs and poly(acrylic acid) (PAA) was systematically investigated. We prepared the micelles by gently adding a selective solvent, water, to a PS240-n-PEO182/N,N-dimethylformamide (DMF) solution. After DMF was removed by dialysis, the diluted micelles were associated with PAA at different pH values. The complexation behavior was studied viia ultraviolet.-visible spectroscopy, laser light scattering, zeta-potential, and transmission electron microscopy techniques. As the pH value varied, the complexation between the PS240-b-PEO182 micelles and PAA behaved differently. At pH < 3.0, the system was in the flocculation region where large aggregates of the micelles formed spontaneously. A single-micelle, stepwise adsorption region could be observed when the pH value was in the range of 3.0-4.8. Above a pH value of 4.8, no adsorption could be found. The value of pH 3.0 was recognized as the onset pH value for the micellar flocculation. At this value, the micelle flocculating rate was very slow, and thus the flocculating process was able to be monitored. A pearl-necklace-like morphology at pH 3.0 was observed, and its formation mechanism was also discussed.