Info

Displacement from the fiber axis (nm)

Figure 1. Radial density profiles, normal to the fiber axis, for a fiber composed of 36 independent parent chains of C100H200 at 509K. The periodicity of the simulation box along the fiber axis, lx, is 11.5, 11.0, 10.5, 10.0, 9.5, 9.0, 8.5, and 5.25 nm, reading from left to right.

Displacement from the fiber axis (nm)

Figure 1. Radial density profiles, normal to the fiber axis, for a fiber composed of 36 independent parent chains of C100H200 at 509K. The periodicity of the simulation box along the fiber axis, lx, is 11.5, 11.0, 10.5, 10.0, 9.5, 9.0, 8.5, and 5.25 nm, reading from left to right.

data at the extreme left hand side ofFigure 1. This statistical problem can be alleviated using an alternative definition of the onset of disruption, using results derived from a larger number of occupied cells.

A larger number of cells can be employed if the focus is shifted from the inside of the fiber to the surface region, where the density is a strong function of distance from the fiber axis. With the initial structure, formed withLX = 5.25 nm, the density profile in the surface region is described by the hyperbolic tangent function in Equation (1). As Lx increases, the density profiles in the surface region initially retains nearly the same shape, but eventually, as Lx continues to increase, the density profiles in the surface region become broader. This broadening shows up in the fits to Equation (1) as in increase in the correlation length, Using the size of as the criterion, the breakup of the fiber treated in Figure 1 has its onset when Lx is 10.0 nm. This identification is consistent with visual inspection of fibers that have been subjected to reverse mapping, which restores the missing carbon and hydrogen atoms.

The total energy (sum of the intramolecular contribution from the rotational isomeric state model and the intermolecular contribution from the discretizedLennard-Jones potential energy function) of the f36 system initially increases as Lx increases, passes through a broad maximum when Lx is near 10 nm, and then slowly decreases. This behavior is consistent with the identification of the onset of the breakup of the fiber at LX = 10 nm, but it is less precise than the identification using because the maximum in the total energy is very broad. The trend for the total energy is dominated by intermodular contributions from the discretized Lennard-Jones potential energy function. There is no apparent trend in the intramolecular energies from the rotational isomeric state model.

Decrease in the Number of Independent Parent Chains

Figure 2 depicts radial density profiles for a series of simulations that initiate with the fiber composed of 76 independent parent chains of C100H202, initially in the periodic box withLx = 5.25 nm, Several of the parent chains are removed from the system, and the perturbed system is then re-equilibrated at 509K. The fiber becomes thinner as chains are removed, but the core retains its integrity with as few as 14 independent parent chains. Disruption of the core of the fiber is readily apparent when the number of independent parent chains decreases to 9.

Decrease in the Degree of Polymerization of the Parent Chains

Figure 3 depicts radial density profiles for fibers in a series of simulations that initiate with the fiber composed of 36 independent parent chains of C100H202, in the periodic box with Lx = 5.25 nm. Several beads are removed from the ends of the parent chains, and the perturbed system is then re-equilibrated at 509K. The fiber retains its integrity when the

Displacement from the fiber axis (nm)

Figure 2. Radial density profiles at 509K, normal to the fiber axis, for a fiber composed of 9,14,18,36, and 72 independent parent chains of C100H202, reading from left to right. The periodicity along the fiber axis, LX, is 5.25 nm.

Displacement from the fiber axis (nm)

Figure 2. Radial density profiles at 509K, normal to the fiber axis, for a fiber composed of 9,14,18,36, and 72 independent parent chains of C100H202, reading from left to right. The periodicity along the fiber axis, LX, is 5.25 nm.

Displacement from the fiber axis (nm)

Figure 3. Radial density profiles at 509K, normal to the fiber axis, for a fiber composed of 36 independent parent chains of C30H62, C40H82, C60H122, C80H162, and C100H202, reading from left to right. The periodicity of the simulation box along the fiber axis, L„ is 5.25 nm.

Displacement from the fiber axis (nm)

Figure 3. Radial density profiles at 509K, normal to the fiber axis, for a fiber composed of 36 independent parent chains of C30H62, C40H82, C60H122, C80H162, and C100H202, reading from left to right. The periodicity of the simulation box along the fiber axis, L„ is 5.25 nm.

parent chains are reduced in length to C80H162, but disruption is apparent when the parent chains are as short as C40H82. The onset of disruption occurs when the chains are reduced in length to approximately CH^.

0 0

Post a comment