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Aromatic polyamides, the most famous of which is poly(p-phenylene terephthalamide) (PPTA), are wellknown for their excellent mechanical properties, thermal stability, and chemical resistance. However, the processing of PPTA is challenging and expensive due to its solubility in only highly aggressive polar solvents and its high melting temperature (~500°C). Therefore, it is desirable to design modified systems
that improve processability without compromising other properties. It was reported that by introducing aliphatic compounds into PPTA crystals, the formed aromatic-aliphatic polyamides, had an improved processability. In this dissertation, molecular dynamics simulations were performed to study the mechanical properties of PPTA and four related aromatic-aliphatic polyamides, PAP5-PAP8. First, the ReaxFF Liu force field was identified to be the optimum force field by comparing nine different reactive and non-reactive force fields in terms of their abilities to reproduce the lattice parameters, hydrogen
bonding, pi-pi stacking, as well as X-ray diffractions of these polyamides. With the optimum force field, stress-strain simulations were performed for PPTA and PAP5 in the chain and transverse directions. Anisotropy was observed for stretching in different directions. Next, the effect of aliphatic chain length was studied by comparing the mechanical properties of PPTA, PAP5-PAP8. This dissertation aimed to establish and quantify relationships between structure, processing, and mechanical properties of highperformance polyamides to ultimately enable rational design of components, devices, and systems with improved performance.
Quanpeng Yang is a Ph.D. candidate in the Department of Mechanical Engineering. He joined Professor Ashlie Martini’s group in January of 2019. His research focuses on studying the mechanical and tribological properties of 2D/nano/crystalline materials. He obtained his Master’s degree in mechanical engineering at South China University of Technology and Bachelor’s degree in mechanical engineering at Guangdong University of Technology.
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