Date of Award

Spring 1-1-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical & Biochemical Engineering

First Advisor

Arthi Jayaraman

Second Advisor

Charles Musgrave

Third Advisor

Yifu Ding

Abstract

We present a two-part computational study that demonstrates and explores new design parameters for the directed assembly of polymer grafted nanoparticles.

In the first part we present a predictive computational materials design study linking molecular features of the polymers to the structure and shape of the assembly of polymer functionalized nanoprisms. Focusing on nanoprisms with polymers grafted on their edges, we systematically vary monomer and solvent chemistry ranging from homopolymers in theta solvent and bad solvent, to AB copolymers with varying A and B solvent selectivity, and ratio of polymer molecular weight to particle size. In the absence of polymer functionalization the nanoprisms aggregate, when grafted with homopolymers in theta solvent the nanoprisms disperse, and when grafted with homopolymers in a bad solvent they assemble into one-dimensional stacks. When grafted with AB diblock copolymers in an A-selective solvent the nanoprisms form shell-like assembled structures. We find signatures of these many-body assemblies in a two-body potential of mean force (PMF) calculated using biased molecular dynamics simulations. For polymer grafted nanoprisms that assemble into stacks we find strong attraction at contact in the PMF, and for polymer grafted nanoprisms that assemble into shells we find strong attraction in the PMF at appropriate inter-particle distances and orientations. As the functionalized polymer chain length to prism size decreases, the tendency to form shells decreases.

We present a molecular dynamics simulation study of systems containing homopolymer grafted particles in a homopolymer matrix, where the graft and matrix polymer chemistries are identical, to elucidate the effect of flexibility of the polymers on the wetting of the grafted layer by the matrix polymer and morphology of the nanocomposite. We find that decreasing flexibility of the grafted and matrix polymers causes the wetting of the grafted layer by the matrix polymers to increase. We also find that this increased wetting is more significantly driven by the graft flexibility than by the matrix flexibility. Due to this improved wetting of the grafted layer, we also observe increased particle dispersion in the polymer matrix.

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