Polydispersity-Driven Block Copolymer Amphiphile Self-Assembly into Prolate-Spheroid Micelles

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Block copolymers self-assemble into various nanostructures in solution.
• Polydispersity, particularly in hydrophobic blocks, can significantly impact self-assembly.
• Understanding these effects is crucial for designing novel materials.

Purpose of the Study:

• To investigate the effect of hydrophobic block polydispersity on the aqueous self-assembly of poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) triblock amphiphiles.
• To correlate polydispersity with the resulting micellar morphologies.
• To understand the formation mechanisms of different aggregate shapes.

Main Methods:

• Synthesis of polydisperse OBO triblock copolymers.
• Characterization of copolymer composition and polydispersity.
• Small-angle neutron scattering (SANS) to study micellar structures in aqueous solutions.
• Varying the weight fraction of the hydrophilic poly(ethylene oxide) block (wO).

Main Results:

• At wO = 0.18, polydispersity led to a mixture of spherical and rod-like micelles and vesicles.
• At higher wO (0.51-0.68), exclusively American football-shaped micelles were observed.
• The distribution of preferred interfacial curvatures, arising from polydispersity, dictates the observed morphologies.
• Intramicellar segregation relieved core block chain stretching, influencing aggregate shape.

Conclusions:

• Hydrophobic block polydispersity in OBO triblock copolymers is a key factor in determining aqueous micellar morphology.
• The resulting distribution of preferred curvatures drives the formation of coexisting or anisotropic micellar shapes.
• This study provides insights into controlling polymer self-assembly through controlled polydispersity.