In situ monitoring of block copolymer self-assembly through controlled dialysis with light and neutron scattering detection

TL;DR

This study introduces a controlled dialysis method with real-time light and neutron scattering to monitor block copolymer self-assembly, revealing detailed phase behavior and kinetic control of structure formation.

Contribution

It presents a novel dialysis cell setup for in situ monitoring of BC self-assembly, enabling detailed phase diagrams and kinetic insights under near-equilibrium conditions.

Findings

Spherical micelles form first, then evolve into rods and vesicles.

Self-assembly structures decrease interfacial area with increasing water content.

Dialysis membrane pore size controls self-assembly kinetics.

Abstract

Solution self-assembly of amphiphilic block copolymers (BCs) is typically performed by a solvent-to-water exchange. However, BC assemblies are often trapped in metastable states depending on the mixing conditions such as the magnitude and rate of water addition. BC self-assembly can be performed under near thermodynamic control by dialysis, which accounts for a slow and gradual water addition. In this Letter we report the use of a specifically designed dialysis cell to continuously monitor by dynamic light scattering and small-angle neutron scattering the morphological changes of PDMS-b-PEG BCs self-assemblies during THF-to-water exchange. The complete phase diagrams of near-equilibrium structures can then be established. Spherical micelles first form before evolving to rod-like micelles and vesicles, decreasing the total developed interfacial area of self-assembled structures in response to increasing interfacial energy as the water content increases. The dialysis kinetics can be tailored to the time scale of BC self-assembly by modifying the membrane pore size, which is of interest to study the interplay between thermodynamics and kinetics in self-assembly pathways.