Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles.

Two different classes of hairy self-suspended nanoparticles in the melt state, polymer-grafted nanoparticles (GNPs) and star polymers, are shown to display universal dynamic behavior across a broad range of parameter space. Linear viscoelastic measurements on well-characterized silica-poly(methyl acrylate) GNPs with a fixed core radius () and grafting density (or number of arms ) but varying arm degree of polymerization () show two distinctly different regimes of response. The colloidal Regime I with a small (large core volume fraction) is characterized by predominant low-frequency solidlike colloidal plateau and ultraslow relaxation, while the polymeric Regime II with a large (small core volume fractions) has a response dominated by the starlike relaxation of partially interpenetrated arms.

Internal Microstructure Dictates Interactions of Polymer-grafted Nanoparticles in Solution.

Understanding the effects of polymer brush architecture on particle interactions in solution is requisite to enable the development of functional materials based on self-assembled polymer-grafted nanoparticles (GNPs). Static and dynamic light scattering of polystyrene-grafted silica particle solutions in toluene reveals that the pair interaction potential, inferred from the second virial coefficient, , is strongly affected by the grafting density, σ, and degree of polymerization, , of tethered chains. In the limit of intermediate σ (∼0.