Propagation of Dislocations and Stress Transmission in Poly(p-phenylene terephthalamide) (PPTA)

Dislocations play a crucial role in determining the deformation of materials yet are still rarely explored in polymers. Employing all-atom molecular dynamics simulations, we directly analyzed the unique structure of quasi-1D dislocations in poly(p-phenylene terephthalamide) (PPTA) induced by an external force, which is drastically different from those in metals. The propagation of dislocations in polymer fibers occurs in two distinct stages: the slow internal propagation and the subsequent rapid extension at chain ends. All results reveal that the ultimate strength of polymer fibers is determined by dislocations rather than breaking chemical bonds. The relationship between stress transmission and dislocation propagation reveals that dislocations are caused by localized motion processes, necessitating a specific stress level to overcome the energy barrier associated with dislocations. The unique nature of dislocations in polymers transcends specific material categories, offering universally applicable insights, as verified by poly(p-phenylene terephthalamide) (PPTA), polyethylene (PE), and polyamide (PA6). Our results provide an in-depth understanding of the dislocation kinetics in polymers.