Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Arthi Jayaraman

Second Advisor

Yifu Ding

Third Advisor

Christopher Bowman

Fourth Advisor

Jennifer Cha

Fifth Advisor

Matthew Glaser

Abstract

Controlling polymer nanocomposite (PNC) morphology is an essential step towards designing PNCs with target macroscopic properties for specific applications. One strategy to control PNC morphology is to modify the surface of the nanoscale filler (nanoparticles) with polymer chains. By tailoring the properties of the grafted and matrix polymers, the effective filler-filler interactions and the PNC morphology can be tuned. The goal of this thesis is to elucidate how physical and chemical design parameters of polymer-grafted particle based PNC impact morphology, in order to engineer new polymer nanocomposite materials.

First, we use Monte Carlo simulations to show how the assembly of copolymer grafted particles in implicit solvent is affected by various grafted layer properties: grafted polymer chemistry, particle-diameter, particle concentration, grafting density, and graft sequence. Despite our focus on isotropically grafted particles, anisotropic particle assembly appears in the simulations over much of the parameter space. We highlight how the blockiness of the graft polymer sequence (number of contiguous like monomers) tunes cluster anisotropy when the outer-block monomers are highly solvo-phobic.

Second, we study homopolymer grafted particles in chemically-identical matrix homopolymer. We examine how polydispersity and flexibility of graft and matrix polymers affect the mixing of the graft and matrix chains, and in turn the dispersion and aggregation of the grafted particles in the matrix. Increasing graft polydispersity or decreasing graft and matrix flexibility increases the mixing of the graft and matrix chains (i.e. grafted layer wetting) and stabilizes the dispersed morphology of the composites.

Finally, we show that for composites where the graft and matrix chains are chemically-dissimilar, the wetting-dewetting and dispersion-aggregation transitions are distinct transitions, unlike what is generally assumed for the chemically identical case. Using temperature, graft-matrix 𝜒, or polymer composition, the degree of wetting of the grafted layer by matrix chains is tuned in the dispersed state. The ability to tune wetting in the dispersed state is not present for chemically-identical composites and reveals the possibility of greater macroscopic property control in composites where the graft and matrix chains are chemically-dissimilar than chemically-identical.

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