2025 Theses Doctoral

Understanding the Properties of Nanocomposites via Computational Methods

Marshall, William C.

Polymer nanocomposites have been in use in tires since the 1940s, and since then have become more prevalent in everyday use. This is due to the enhanced properties, relative to neat polymer, of these hybrid materials. These properties include thermal, mechanical, electrical, and transport properties and are strongly dependent on the dispersion state of the embedded nanoparticles. A common way to control the dispersion state of these nanoparticles is to chemically graft polymers on the surface of the nanoparticles, however this method is more difficult to implement into everyday use. These grafted polymers have dramatically different properties than that of bare nanoparticles embedded in a polymer matrix. In order to understand the behavior of nanocomposites, we study both grafted nanoparticles and bare particles.

In this thesis, we first try to use data scraped from literature to understand which factors most strongly influence bare nanoparticle dispersion. This, however, was deemed to be ambiguous due to the dataset used. Therefore, the next chapter we create our own experimental dataset, to further build understanding of what drives bare nanoparticle dispersion. These chapters use machine learning and knowledge of the physics of the system to determine that electrostatic repulsions and the formation of a bound layer are the best predictors of the dispersion state. The following chapters we turn to studying grafted nanoparticles. In chapter 4, we develop a model to test the hypothesis that there are two “channels” in series for gases to diffuse through densely grafted nanoparticles films. In the final chapter, we look at how two grafted nanoparticles interact in a polymer matrix. We find that when the grafted polymers cannot interpenetrate, the grafted nanoparticles behave as soft spheres where the chains must push other chains out of the way. These insights allow us to grasp both the formation of the nanocomposite films, and the corresponding properties of these novel materials.