Paper Number
SM3 

Session
Polymer Solutions & Melts

Title
Dynamics of polymer-grafted nanoparticles in solutions of linear polymer investigated using neutron and x-ray scattering techniques

Presentation Date and Time
February 13, 2017 (Monday) 10:50

Track / Room
Track 5 / Snowy Egret

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
Grafting particles with polymers enhances particle dispersion in high molecular weight polymer solutions and melts and thereby increases the storage modulus of composite materials. To disperse the particles in these materials requires an understanding of the dynamics of polymer-grafted nanoparticles. When the grafted polymer is small compared to the particle, the dynamics of a grafted particle are similar to those of a bare particle. In the opposite limit, when the grafted polymer is much larger than the particle, the grafted particle dynamics are similar to those of a star polymer. Between these two limits, the dynamics of grafted nanoparticles are poorly understood. We dispersed silica particles grafted with high molecular weight polystyrene in solutions of linear polymer of various molecular weight and concentration. The molecular weights span the entanglement molecular weight Me in solution. Exploiting the difference in scattering contrast between neutrons and x-rays, we measured the relaxations of both grafted polymer chains and of the silica cores. Over length scales less than 20 nm and time scales less than 100 ns, the relaxations of grafted chains were markedly different than those of free polymer. The grafted chains relaxed diffusively but were confined by neighboring chains. The confining length scale decreased with matrix concentration and was independent of matrix molecular weight. On length scales larger than 50 nm and time scales longer than 1 ms, the grafted nanoparticles moved diffusively at low matrix molecular weights and subdiffusively at high matrix molecular weights, due to polymer entanglements. Our results indicate that the matrix polymer in a semidilute solution confines the grafted polymer and slows particle relaxations, especially at high matrix molecular weights. When the grafted polymer is similarly sized to the particle core, the particle dynamics depend on the relaxations of the grafted polymer, with implications for targeted drug delivery and rheology on composite materials.