Molecular Dynamics in liquid-like Polyethylenimine-based Nanoparticle Organic Hybrid Materials*

We have employed broadband dielectric spectroscopy (BDS), rheology, and nuclear magnetic resonance spectroscopy (NMR) to study molecular dynamics in nanoparticle organic hybrid materials (NOHMs) comprising 20 wt% silica nanoparticles ionically-bonded to a polyethylenimine canopy. By comparing the neat polymer – used as a canopy – to the derivative NOHMs, we find that timescales characterizing segmental dynamics in the NOHM are identical to those for the neat polymer as determined by BDS. Rheology, however reveals slower dynamics for the NOHMs. Detailed analysis of the carbon-spin lattice relaxation times yields mechanistic insights into localized and collective dynamics, in quantitative agreement with dielectric results. Interestingly, the NOHMs retain liquid-like characteristics unlike conventional polymer nanocomposites but exhibit higher viscosity due to additional contributions from tethered polymer chains. These findings demonstrate the potential of achieving unique and desired material properties via NOHMs by an informed choice of the constituent materials.