Complex pH-Dependent Interactions between Weak Polyelectrolyte Block Copolymer Micelles and Molecular Fluorophores.

Area of Science:

• Polymer science
• Materials science
• Nanotechnology

Background:

• Amphiphilic block copolymers with polyelectrolyte blocks form stimulus-responsive nanostructures.
• Applications in drug delivery, biomimetics, and sensing rely on polyelectrolyte swelling with pH or ionic strength changes.
• Interfacial interactions tuned by deprotonation are less studied than morphological swelling.

Purpose of the Study:

• Investigate if pH-driven morphological changes in polyelectrolyte nanostructures affect their interactions with solution molecules.
• Use polybutadiene-block-poly(acrylic acid) (pBd-pAA) micelles as a model system.
• Probe micelle-solute interactions as a function of solution pH.

Main Methods:

• Utilized a Förster resonance energy transfer (FRET) approach to measure micelle-fluorophore proximity.
• Monitored micelle corona thickness changes with pH.
• Quantified fluorophore affinity for micelles using dialysis experiments at varying pH.

Main Results:

• pAA corona thickness increased monotonically with pH.
• FRET efficiency showed complex, nonmonotonic behavior with pH, decoupling from simple swelling.
• Dialysis confirmed pH-dependent affinity of pAA for fluorophores drives FRET changes, not just corona shape.

Conclusions:

• Interfacial interactions of polyelectrolyte nanostructures with solutes are governed by pH-dependent binding affinity.
• Morphological swelling alone does not dictate nanostructure-solute interactions.
• Findings are vital for designing effective stimulus-responsive materials for various applications.