Exchange lifetimes of the bound polymer layer on silica nanoparticles

Decades of research have emphasized the importance of a bound layer i.e. a thin layer of immobilized polymer adsorbed on the surface of a nanoparticle, as an important factor in determining the material property improvements in polymer nanocomposites (PNCs). By utilizing the contrast difference between partially deuterated poly (2-vinylpyridine) (P2VP) adsorbed on the surface of SiO₂ nanoparticles (NPs) suspended in a hydrogenated P2VP, a reduction in apparent bound layer thickness was observed with time at elevated temperatures, with the process being highly temperature dependent. This suggests that the bound layer can desorb from the surface at elevated temperatures, with the temperature dependence arising from the different valencies of the adsorbed polymer chains. Going beyond the structural reorganization of the bound layer, recent work has also observed long term structural reorganization of the NPs in a traditional PNC as well. As with the bound layer, this process is also highly activated and is observable at length scales well beyond the size of the matrix polymer chain or the bound layer. This opens up new avenues of controlling the structure and thermomechanical properties of PNCs using elevated temperatures.