Paper Number
PO47 

Session
Poster Session

Title
Structure and dynamics of nanoparticles and polymer in model polymer solutions with particle-particle interactions

Presentation Date and Time
February 15, 2017 (Wednesday) 6:00

Track / Room
Poster Session / Foyer-Stairs/Windows

Authors (Click on name to view author profile)

1. Poling-Skutvik, Ryan (University of Houston, Chemical and Biomolecular Engineering)
2. Conrad, Jacinta C. (University of Houston)
3. Krishnamoorti, Ramanan (University of Houston)

Author and Affiliation Lines (in printed abstract book)
Ryan Poling-Skutvik, Jacinta C. Conrad, and Ramanan Krishnamoorti
University of Houston, Houston, TX

Speaker / Presenter 
Poling-Skutvik, Ryan

Text of Abstract
The bulk rheology of polymer nanocomposites deviate significantly from that for pure polymer melts due to competing relaxations of both particles and the surrounding polymer. We investigate these competing relaxations with a model system of charged silica nanoparticles (50 nm in diameter) dispersed in semidilute solutions of high molecular weight polystyrene (of radius of gyration 30 nm). We probe the structure of the silica nanoparticles using static x-ray and of the polymer using small angle neutron scattering. The particles are well dispersed and the polystyrene chains are Gaussian with a correlation length of 4 nm that agrees with polymer scaling laws. We then use dynamic scattering methods to independently quantify the dynamics of polymers and particles. Using neutron spin echo spectroscopy, we show that the polymer chains relax according to the Zimm model, with hydrodynamic coupling over the correlation length. The polymer dynamics are unchanged in the presence of particles; the polymer chains do not hydrodynamically couple to the particle. Using x-ray photon correlation spectroscopy, we show that the nanoparticle dynamics are subdiffusive with stretched exponential decays. The subdiffusive dynamics derive from a coupling between the particle dynamics and the polymer relaxations over the particle surface. Over the interparticle distance, the particle dynamics are suppressed and inversely correlated to the structure factor, as observed in many homogeneous materials with diffusive dynamics. Notably, the de Gennes narrowing of the particle dynamics persists despite the coupling of particle and polymer dynamics on shorter length scales and the resulting subdiffusive particle dynamics. Exploiting contrast variation in x-rays and neutrons, we separated changes in the particle dynamics from those of the polymer. Thus, we developed a nanoscale understanding of the complex, competing relaxations present in composite materials.