Effects of Polymer Side-Group Size on Interfacial Mechanics of Graphene-Polymer Nanocomposites
Date of Award
Master of Science (MS)
Dr. Zhaoxu Meng
Dr. Huijuan Zhao
Dr. Zhen Li
Graphene-reinforced polymer nanocomposites possess excellent mechanical, thermal, and electrical properties, which make them promising candidates for various applications. Favorable interfacial interactions and mechanics between graphene sheets and polymer matrices are often essential to achieve superior mechanical properties. Nevertheless, it remains largely elusive how molecular features of polymer systems, particularly the side-group size of polymer chains, affect the interfacial mechanics between graphene sheets and polymer matrices, primarily due to challenges in well controlling these features in experiments. On the other hand, exploring their roles in the mechanical properties of graphene-polymer nanocomposites is very expensive to study with all-atomistic molecular dynamics (MD) simulations.
In this thesis, I employed molecularly-informed coarse-grained (CG) models to investigate the role of polymer side-group size in interfacial mechanics between methacrylate-based polymer matrices and a graphene sheet embedded within. In order to specifically look into the effect of side-group size, the van der Waals radius of the side-group beads in the two-bead-per-monomer CG model of polymer chains is altered to four different values. At the same time, the other structural and force field parameters remain the same. I have conducted MD simulations to systematically examine the interfacial energy and interfacial shear mechanics between a graphene sheet and polymer matrices. The results of the simulations show that the interfacial energy between the graphene sheet and polymer chains decreases as the side-group size increases, which is attributed to the difference in the local packing density of polymer chains near the graphene sheet. In addition, I have implemented the steered molecular dynamics technique to pull the graphene sheet out of polymer matrices, which resembles the single fiber pull-out technique traditionally used to characterize the interfacial properties between fibers and polymer matrices. By comparing the potential of mean force (PMF) during the graphene pull-out process, which marks the amount of work needed to pull the graphene out of the polymer matrix, the results show that changes in the side-group size also lead to significant differences in the PMF results, although with a varying dependence on side-group size. This observation demonstrates that the interfacial shear mechanics depend on other factors in addition to the local packing density of polymer chains.
This thesis reveals that the size of the polymer side-group may be a key molecular feature that influences the interfacial properties between nanofiller and polymer matrices for nanocomposites. Our computational approach can generally be applicable to other nanocomposite systems to understand the roles of other molecular features.
Brokaw, Grace, "Effects of Polymer Side-Group Size on Interfacial Mechanics of Graphene-Polymer Nanocomposites" (2022). All Theses. 3929.