Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Arthi Jayaraman

Second Advisor

Robert P. Parson

Third Advisor

Won Park

Fourth Advisor

Scott Sides

Fifth Advisor

Yifu Ding

Abstract

Macroscopic properties of polymer nanocomposites are fundamentally linked to the morphology (or assembled structure) of its constituents. In order to design composites to have specific macroscopic properties it is important to be able to control the assembly of the constituents in the composite. In this thesis we use molecular simulations to study the molecular-level interactions and assembly of one class of polymer nanocomposites, namely diblock-copolymer grafted nanoparticles in solvent and in polymer matrix.

First, we study how the molecular features of the diblock-copolymer grafts affect the assembly of grafted nanoparticles in a (implicit) small molecule solvent. Using coarse-grained molecular dynamics simulations we study the effects of graft length, particle size, solvent selectivity, and copolymer composition on the particle assembly. This knowledge informs experiments on what diblock copolymer grafted nanoparticles properties to synthesize to achieve a target assembled structure.

Second, we elucidate how the chemistry of a homopolymer matrix affects the graft and matrix polymer conformations and the interactions between diblock copolymer grafted particles in the homopolymer matrix. Using coarse-grained simulations and umbrella sampling technique we calculate the potential of mean force between two grafted particles within polymer matrix. We vary the chemistry of the homopolymer matrix and the copolymer grafts through systematic variations in the monomer interaction potentials. This gives insight into how the diblock copolymer grafted layer and the matrix environment influence the effective interactions between the particles in a polymer matrix.

Third, we investigate diblock copolymer grafted particles as compatibilizing agents in a polymer matrix consisting of an immiscible homopolymer blend. The phase separation of homopolymers within the blend leads to formation of domains and interfaces that weaken the composite materials' mechanical properties. There is a need optimal compatibilizers that stabilize these polymer interfaces in the blend, and as a result strengthen the composite material. Using simulations we compare the compatibilizing properties of diblock copolymer grafted particles to those of other compatibilizers, such as free diblock copolymers and Janus nanoparticles. Beyond their role as superior compatibilizers, we also find that diblock copolymer grafted nanoparticles provide control over the glass transition temperature of the polymer nanocomposite.

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