Spatiotemporal Formation Kinetics of Polyelectrolyte Complex Micelles with Millisecond Resolution

27 July 2020, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We have directly observed the in situ self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. A synthesized neutral-charged diblock polycation and homopolyanion that we have previously investigated as a model charge-matched, core-shell micelle system were selected for this work. The initial micellization of the oppositely charged polyelectrolytes was completed within the dead time of mixing of 100 ms, followed by micelle growth and equilibration up to several seconds. By combining the structural evolution of the radius of gyration (Rg) and aggregation number (N) with complementary molecular dynamics simulations, we develop new information on how the self-assemblies evolve incrementally in size over time through a two-step kinetic process: first, oppositely-charged polyelectrolyte chains pair to form nascent aggregates that immediately assemble into spherical micelles, and second, these PEC micelles grow into larger micellar entities. This work has determined one possible kinetic pathway for the initial formation of PEC micelles, which provides useful physical insights for increasing fundamental understanding self-assembly dynamics driven by polyelectrolyte complexation that occur on ultrafast timescales.

Keywords

Polyelectrolytes
Polymers
Micelles
Coacervates
SAXS
Kinetics

Supplementary materials

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