Molecular dynamics modeling of PPTA crystallite mechanical properties in the presence of defects

Abstract

The mechanical properties of PPTA crystallites, the fundamental building blocks of aramid polymer fibers such as Kevlar ® and Twaron ® , are studied here using molecular dynamics simulations. The ReaxFF interatomic potential is employed to study crystallite failure via covalent and hydrogen bond rupture in constant strain-rate tensile loading simulations. Emphasis is placed on analyzing how chain-end defects in the crystallite influence its mechanical response and fracture strength. Chain-end defects are found to affect the behavior of nearby chains in a region of the PPTA crystallite that is small relative to the typical crystallite size in manufactured aramid fibers. The central C-N bond along the backbone chain is identified as the weakest in the PPTA polymer chain backbone in dynamic strain-to-failure simulations of the *

Preparation of High Strength and Toughness Aramid Fiber by Introducing Flexible Asymmetric Monomer to Construct Misplaced‐Nunchaku Structure

“…[ 7,8 ] As a representative of high‐performance fibers, poly (p‐phenylene terephthalamide) (PPTA) fiber has remarkable mechanical properties and thermal stability due to the rigid‐chain structure. [ 9–11 ] However, due to the presence of phenyl group and amide bonds in the main chain of PPTA, the highly rigid chain results in insufficient toughness of PPTA. [ 12,13 ] When the fiber is impacted, the low energy absorption caused by low toughness makes the fiber structure easy to be destroyed.…”

Atomistic simulations of functionalization of aramid fiber‐epoxy nanocomposite

“…The atomic topological files based on the X‐ray diffraction data of AF were used to create a molecular model. Figure 1a shows orthogonal crystalline unit cell in the x, y, and z directions 22–24 . In order to certificated that simulation crystalline cell could more closely replicate the experimental measurement, the bulk crystalline cells consisting of 4*8*4 unit cell in the x, y, and z directions (See Figure S1b in Data S1) were equilibrated at a temperature of 300 K and 0.0001 GPa pressure for 100 ps.…”

“…The silane coupling agent molecule was directly copied onto the functionalized fiber surface (See Figure S2b in Data S1). In MD simulations of AF and epoxy resin, the established models were computed using the Condensed‐phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field 22,27–32 . The system was minimized to 10,000 steps; thereafter, the constant pressure and temperature (NPT) was run for 100 ps, followed by the constant atom number, volume and temperature (NVT) for 100 ps to allow the filler surface to be completely wetted by the polymer.…”

“…Figure 1a shows orthogonal crystalline unit cell in the x, y, and z directions. [22][23][24] In order to certificated that simulation crystalline cell could more closely replicate the experimental measurement, the bulk crystalline cells consisting of 4*8*4 unit cell in the x, y, and z directions (See Figure S1b in Data S1) were equilibrated at a temperature of 300 K and 0.0001 GPa pressure for 100 ps. After equilibration, values measured include the unit cell dimensions, bond lengths and angles, Young's modulus.…”

“…In MD simulations of AF and epoxy resin, the established models were computed using the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field. 22,[27][28][29][30][31][32] The system was minimized to 10,000 steps; thereafter, the constant pressure and temperature (NPT) was run for 100 ps, followed by the constant atom number, volume and temperature (NVT) for 100 ps to allow the filler surface to be completely wetted by the polymer. The control of temperature and pressure of the process was carried out following the Andersen and Hans 33 and Berendsen methods, 34 respectively.…”