Spatiotemporal Formation and Growth Kinetics of Polyelectrolyte Complex Micelles with Millisecond Resolution

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 chargematched, 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 (R g ) with complementary molecular dynamics simulations, we show 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 occurs on ultrafast time scales.

100th Anniversary of Macromolecular Science Viewpoint: Attractive Soft Matter: Association Kinetics, Dynamics, and Pathway Complexity in Electrostatically Coassembled Micelles

“…Tirrell and co-workers conducted time-resolved SAXS experiments on longer dbps (PVBTA 53 - b -PEO 112 and PVBTA 100 - b -PEO 225 ) mixed with the weak polyelectrolyte PAA 158 . 67 In good agreement with their molecular dynamics simulations, the trSAXS experiments showed charge-neutral clusters formed within the 100 ms of experimental dead time, which rearranged into small equilibrium micelles ( R H = 10 nm) within a matter of seconds. The kinetic profiles also suggested that micellar fusion–fission events are unlikely.…”

“…Interestingly, this second, slow relaxation process was concentration-independent, suggesting that the equilibration is driven mainly by the exchange of polymer chains rather than fusion and fission of (pre)­micelles. Tirrell and co-workers conducted time-resolved SAXS experiments on longer dbps (PVBTA 53 - b -PEO 112 and PVBTA 100 - b -PEO 225 ) mixed with the weak polyelectrolyte PAA 158 . In good agreement with their molecular dynamics simulations, the trSAXS experiments showed charge-neutral clusters formed within the 100 ms of experimental dead time, which rearranged into small equilibrium micelles ( R H = 10 nm) within a matter of seconds.…”

Nanostructured Multiphase Condensation of Complex Coacervates in Polymerization-Induced Electrostatic Self-Assembly

“…Taken together, these results indicate that the parent droplets recruited anionic free chains, cationic growing chains, and the nascent clusters via a kinetically dictated “repulsion–insertion mechanism" as described by Tirrell and Lund, leading to the kinetically dictated condensation-driven hierarchical assembly through the programmed recruitment of these active gradients from the dynamic evolving aqueous medium of LLPS-PIESA.…”

Polyelectrolyte Complex-Covalent Interpenetrating Polymer Network Hydrogels

“…PEC hydrogels self-assemble swiftly [65][66][67][68] upon mixing of aqueous solutions of oppositely charged block polyelectrolytes (bPEs) based on poly(ally glycidyl ether)98poly(ethylene oxide)455-poly(ally glycidyl ether)98 (PAGE-PEO-PAGE). The PAGE blocks were functionalized with ionic (guanidinium and sulfonate) moieties [1] (Figure 1A, row 1).…”