Stability Of The Model Of The Nanofiber

In this section we present new results on the stability of the models of the nanofibers. Destabilization of the model can be achieved in several ways, which include an increase in the length of the periodicity, L x, along the fiber axis, a decrease in the number of independent parent chains, or a decrease in the degree of polymerization of the parent chains. Each change causes the fiber to become thinner. At some point the fiber breaks up into individual droplets, because the spherical shape will minimize the ratio of surface area to volume in the system.

Increase in the Length of the Periodicity along the Fiber Axis

Two different nanofibers of C100H202 were studied. One system (f36) contained 36 independent parent chains, and the other system (f72) contained 72 independent parent chains, both in boxes in which LX was initially 5.25 nm. The simulation protocol for collapse of the fiber consisted of a cycle of increasing Lx by 0.25 nm, followed by relaxation for 105 Monte Carlo steps at a temperature of 509K. This cycle was continued until collapse was observed. The smaller system with 36 independent parent chains collapsed to droplets when Lx reached 10 nm. The larger system, with 72 independent parent chains, did not collapse even when Lx exceeded the length of the fully extended chain, which is 12.5 nm.

Figure 1 depicts radial density profiles, measured normal to the fiber axis, for the f36 system at several values of Lx. This figure suggests two different methods for detecting the onset of the breakup of the fiber. One method uses the density at the core of the fiber. In the initial system, with L X = 5.25 nm, there is an extensive region inside the fiber where the density is constant at about 0.72-0.73 g/cm3, which is a reasonable value for pbulk at this temperature. This region of constant density is reduced in extent as Lx increases. Eventually no part of the system, measured relative to the initial fiber axis, retains a density as high as 0.7 g/cm3. One way of defining the point at which break-up of the fiber occurs is to identify that point with the loss of the region at the core where the density is constant at pbulk. However, this method is subject to statistical error. It relies heavily on events in a relatively small number of cells (those very close to the initial fiber axis), and therefore is subject to a high statistical uncertainty, as is evident from the scatter in the

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