Simulation of an amorphous polyethylene nanofiber on a high coordination lattice

Abstract

Monte Carlo simulations of polyethylene (PE) melts and thin films have previously been performed on the second nearest neighbor diamond (2nnd) lattice by including short and long range interactions. A fiber can be obtained from equilibrated thin film snapshots by increasing another (normal to thin film plane) periodic side to infinity. There is only one effective periodic boundary condition in the simulation. The presence of attractive long range interactions gives cohesion to the fiber. PE fibers, which contain up to 72 chains of C99 and have the radius ≈ 5.0 nm, have been produced and equilibrated on the 2nnd lattice. In these fibers, the density profiles are hyperbolic, with end beads being more abundant than the middle beads at the surface. There are orientational preferences at the surface on the scale of individual bonds and whole chains. Comparison of fibers with different thickness, which contain different number of chains, does not indicate any significant differences in local and global equilibrium properties – for thickness in the range 5.6 to 7.6 nm. Surface energies are calculated directly from the on‐lattice energetics and presented as a function of the fiber radius

Topological effects on static and dynamic properties in an amorphous nanofiber composed of cyclic polymers

“…The new simulations reported here employ 36 cyclic chains. The results are compared with those obtained with similar simulations, reported earlier, [26,27] in which the system contains 36 linear chains with the same number of beads.…”

“…[24,25] Then another side of the box is also extended to 16.5 nm, and another equilibration gives the model for the fiber, with the axis of the fiber oriented along the shortest axis of the periodic box. [26] Simulations of the fiber are performed for two million Monte Carlo Steps (MCS), after equilibration periods of two to three million MCS. The new simulations reported here employ 36 cyclic chains.…”

“…The data become unreliable for displacements larger than Radial density profiles at 509 K for fibers composed of cyclic (continuous) and linear (broken line) chains. The data for the latter fiber is from Vao-soongnern et al [26] 4 nm. The number of observations is also very small as the distance from the fiber axis approaches zero, as in the cylindrical problem the volume of a shell is proportional to 2pr dr, r being the distance from the axis and dr the thickness of the shell.…”

“…1), S for internal chords (those not at a chain end) becomes slightly positive, indicating a tendency for these chords to align parallel to the axis of the fiber. The terminal chords in the fiber composed of linear chains show the opposite trend in the surface region, but they are small The data for the linear chains is from Vao-soongnern et al [26] Fig. 3.…”

“…Distribution of the center of mass of the cyclic (continuous line) and linear (broken line) chains. The data for the linear chains is from Vao-soongnern et al [26] enough in number so that they cannot overcome the trend established by the internal chords in this fiber. This behavior is reminiscent of the ordering patterns observed previously for the chords in simulations of free-standing thin films.…”