Doctoral Dissertations

Date of Award

8-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Alexei P. Sokolov

Committee Members

Mark Dadmun, Takeshi Egami, Adriana Moreo, Jaan Mannik

Abstract

Considerable progress has been made in understanding the miscibility and morphology of polymer nanocomposites (PNCs). However, to date, there is little understood concerning the modification of segmental mobility at the polymer-nanoparticle interface, which due to prevalence of interfaces in PNCs, will predominately control the viscoelastic and mechanical properties of these materials.

In this dissertation, static and dynamic experimental techniques are combined to identify the specific parameters controlling the modification of segmental dynamics at the polymer-nanoparticle interface in the model system of poly(2-vinyl pyridine)/silica nanocomposites. In general, the experimental results clearly demonstrate that the segmental dynamics at the polymer-nanoparticle interface are suppressed relative to the bulk-like polymer and moreover that this effect is dependent on the molecular weight (MW) of the polymer matrix. Additionally, the density of the polymer-nanoparticle interface was found to unexpectedly decrease with increasing MW. These unexpected results indicate a competition between a suppression due to adsorption and a speeding up due to the reduction in density--which suggests that the chain packing at the polymer-nanoparticle interface becomes frustrated at higher MWs. Lastly, by comparing the strength of the polymer-nanoparticle interaction and molecular weight, it is proposed that the orientational anisotropy of the chain conformations primarily controls the magnitude of the dynamic suppression at the polymer-nanoparticle interface and suggests a new way to tailor the segmental dynamics on the nanoscale.

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