NMR Characterization of Canopy Dynamics in Nanoscale Ionic Materials

Abstract

Nanoscale ionic materials (NIMs) are organic-inorganic hybrids in which a core nanoparticle is functionalized with a covalently attached corona and an ionically tethered polymer canopy. NIMs exhibit liquid-like character under ambient conditions in the absence of solvent and are of interest for a variety of applications. We have used nuclear magnetic resonance (NMR) relaxation and pulsed-field gradient (PFG) diffusion experiments to measure the canopy dynamics of NIMs prepared from 18-nm silica nanoparticles. NMR studies show that the fast (ns) local dynamics of the canopy are insensitive to the presence of the silica nanoparticles. Canopy diffusion in the NIMs is slowed relative to the neat copolymer, but not all canopy molecules are slowed equally due to crowding at the nanoparticle surface, resulting in a strongly bound fraction at the surface and a weakly bound outer sphere. Electrostatic interactions with other ionic (Na+) species alter the dynamics by screening interactions with the nanoparticle.