Semi-crystalline fibers, such as Nylon, Dacron, Rayon, and Spectra, play crucial roles in many applications ranging from everyday apparel to advanced biomedical and aerospace components. Typically, these fibers are formed under the application of an applied flow field, which orients the fibers sufficiently to induce the crystallization event. Because of the complexity of the crystallization process, little theoretical modeling has been devoted to describing the kinetics and morphological development of the crystalline structure within these fibers.
In this presentation, the results of nonequilibrium Monte Carlo simulations are described for an atomistic model of a dense liquid composed of linear polyethylene chains undergoing uniaxial elongational flow. The simulations were conducted at four temperatures ranging from 300 K to 450 K. At the higher temperatures of 400 K and 450 K, simulation results revealed that the polyethylene chains were stretched significantly as a function of flow strength, but that the systems remained in the liquid phase. At the lower two temperatures of 300 K and 350 K, clear evidence was obtained of a flow-induced phase transition to a crystalline solid phase. This evidence included a structure factor for the multi-chain system that compared favorably with an experimental x-ray diffraction measurement of a crystalline linear polyethylene at all relevant length scales, including Bragg peaks at the correct wavenumber values. Simulated values of the internal energy (and the configurational temperature) revealed a flow-induced jump in absolute value, reminiscent of a first-order phase transition. A distinct flow-induced enthalpy change was also evident between the liquid and crystalline states, which compared favorably with the experimental quiescent value.