Seminar

Grafting polymer chains on nanoparticles is an efficient method for synthesizing nanocomposites immune from phase separation. However, grafting induces interesting features in the dynamics and structure of the polymer chains. We probe the dynamics in grafted polymers using a combination of quasielastic neutron scattering (QENS), dielectric spectroscopy and rheology. QENS experiments show a molecular weight dependent segmental dynamics in grafted polymers. While the low molecular weight polymer shows retardation of segmental mobility, the high molecular weight shows an acceleration. The traditional method of analysis i.e. a stretched exponential fit is unable to capture the origin of such molecular weight dependent dynamics. We invoke a detailed analysis method using distribution of relaxation times to fit the data which reveals the presence of location dependent dynamics in nanocomposites. We further probe the location dependency of the topological constraints in grafted chains using rheology. We present a Rouse mode analysis for weakly entangled polymer melt as well as grafted polymers. Without assumption of an entanglement tube the Rouse mode analysis accurately captures the location dependent topological confinements along with the monomer dynamics. These constraints are quantitatively related to the assembly of grafted nanoparticles using small angle X ray scattering, which indicate that the grafted nanoparticle assembly is governed by the entropic loss of grafted polymer. The simple approach of Rouse mode analysis is able to capture these constraints without invoking more involved analysis like the Doi-Edwards tube model. Therefore, using quasielastic neutron scattering, dielectric spectroscopy, SAXS and rheology, we are able to interpret the dynamics and conformation of grafted polymer chains in context of the assembly of the nanoparticles.