Aggregation Behavior of Asymmetric Diblock Polyampholyte in Aqueous Solution over a Wide Range of pH and Ionic Strength

The aggregation behavior of the asymmetric diblock polyampholyte poly(2-(dimethylamino)ethyl methacrylate-block-poly(acrylic acid) (PDMAEMA(86)-b-PAA(24)) is studied by static and dynamic light scattering techniques (S/DLS) in aqueous solutions. The molecular assemblies formed by this copolymer are monitored in pure water and over a wide pH range. At pH 5.5, where both blocks are ionized, spherical polymer micelles with hydrodynamic radius (R-H) around 124 nm are detected. These micelles are composed of a large and highly hydrated core formed by the electrostatic complexation between the oppositely charged blocks, and a corona formed by the uncompensated cationic PDMAEMA chains. By combining the results of light scattering, small angle X-ray scattering (SAXS), and cryogenic transmission eletron microscopy (Cryo-TEM) techniques and the predictions of theoretical models from the literature, an aggregation model is proposed, similar to already described crew-cut micelles. These aggregates display resistance to high ionic strengths, suggesting a transition from electrostatic to hydrophobic intermolecular interactions accounting for micelle formation, which is confirmed by the increased incorporation of a hydrophobic probe. The persistence of the aggregates even in conditions at which one of the blocks displays no charge (at extreme pH values) or with high salt concentration, is attributed to remaining hydrogen bonding or hydrophobic interactions that contribute to the core formation.

Automated summary

The aggregation behavior of the asymmetric diblock polyampholyte poly is studied in aqueous solutions, showing the formation of spherical polymer micelles with a highly hydrated core and an outer corona in a wide pH range. These aggregates display resistance to high ionic strengths, suggesting a transition from electrostatic to hydrophobic intermolecular interactions accounting for micelle formation. The persistence of the aggregates in extreme pH values or high salt concentration is attributed to remaining hydrogen bonding or hydrophobic interactions contributing to the core formation.