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

Abstract

Solution self-assembly of amphiphilic block copolymers (BCs) is typically performed by solvent to water exchange. However, BC assemblies are often trapped in metastable states depending on the mixing conditions, such as the magni-tude 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 communication we report the use of a specifically de-signed dialysis cell to continuously monitor by dynamic light scattering and small-angle neutron scattering the mor-phological changes of PDMS-b-PEG BCs 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.