Polyelectrolytes are macromolecules with a substantial fraction of ionizable monomeric building blocks. When constructed into blocky architectures, oppositely–charged polyelectrolyte chains can self–assemble into micellar nanoparticles in water and respond to environmental changes in pH, salt, and temperature; these tunable features have motivated concerted efforts to integrate such materials into a diverse host of bioapplications, ranging from therapeutic polyplexes for delivering genetic payloads to soft underwater adhesives for repairing tissues between skin and bones. However, understanding how to balance the chemical and electrostatic interactions in charged structures has proven to be a longstanding unresolved problem for functional utility, where stable assemblies must be (1) produced with consistent repeatability, and (2) capable of exhibiting controlled storage/release. In pursuit of these goals, we report detailed insight into the fundamentals of solution complexation, evolution, and disassembly from a molecular engineering perspective. In a carousel parallel synthesizer, libraries of well–defined block polycations and polyanions were prepared at various neutral-to-charge chain lengths using aqueous reversible-addition fragmentation chain transfer (RAFT) polymerization. The structural assembly and ordering of model diblock and triblock systems were investigated using complementary small angle X–ray/neutron scattering and rheology; we further labeled individual polyelectrolyte chains with fluorescent tags to study the solution dynamics of complexation. At low concentrations, kinetically–trapped nanoaggregates were observed in certain systems, which enabled the opportunity to explore the role of salt in processing charged micelles. The temporal breakup of equilibrating micelles was monitored with time-resolved light scattering and cryogenic transmission electron microscopy, elucidating characteristic relaxation times of different pairings of polyelectrolytes. This fusion/fission phenomenon of complex–core micelles in response to salt evokes interesting, analogous comparisons to how temperature anneals non-equilibrium amphiphilic micelles.

Life of the polyelectrolyte: Complexation, evolution, and disassembly

256th National Meeting (2018)

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