Temperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona

In aqueous solutions at room temperature, poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP38-b-PEO211 and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA55-b-PNIPAAm88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO3, T = 25, and 60 °C, that is, below and above the LCST of 32 °C. At T = 25 °C, C3Ms were observed for 7 < pH < 12 and NaNO3 concentrations below 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 °C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.