Polyelectrolyte complexes form by mixing two oppositely charged polymers in solution. This phenomenon results in either complex coacervation which is a liquid-liquid phase separation or solid precipitate formation. Electrostatic interaction between a diblock copolymer of a neutral block and a charged block, with an oppositely charged polymer leads to the formation of nanoscale polyelectrolyte complex (PEC) micelles with a PEC core and neutral corona. PEC micelles have applications in the delivery of charged therapeutics, such as nucleic acids. This work explores using a thermosensitive polymer, poly(N-isopropyl acrylamide)(pNIPAM), as the neutral block. pNIPAM has a lower critical solubility temperature (LCST), above which a hydrophilic to hydrophobic transition occurs. This transition could lead to a core-corona inversion which could facilitate the release of molecules from within the PEC core, leading to potential applications in controlled release drug delivery. We are characterizing micelles formed using a diblock copolymer of pNIPAM-poly(acrylic acid) with (1) poly(lysine) and (2) poly(ethylene glycol)-<i>b</i>-poly(lysine) to investigate the effect of corona stabilization and micelle morphology, before and after temperature transition, including a comparison between a single-corona and a dual-corona stabilized micelle. Dynamic light scattering, small angle x-ray scattering, and electron microscopy are used to characterize micelle structure as a function salt concentration, polymer concentration, charge ratio, pH, and temperature, which are all parameters known to affect polyelectrolyte complex formation. Preliminary results indicate that single-corona micelles form worm-like geometries, while dual-corona micelles form spherical geometries below the LCST. Above the LCST, both micelles begin to aggregate as expected, but the structure of the aggregates is vastly different. Both micelles appear to be completely reversible, returning to their original structure after cooling back down below the LCST.

Characterization of single- vs. dual-dorona thermoresponsive polyelectrolyte complex micelles

2019 Spring National Meeting

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