| The special properties of polymer fibers have a direct bearing to their underlying morphological detail which in turn ties up closely with the processing history of the polymer fiber during melt spinning. Modeling the interaction of the flow-induced deformation within the polymer melt requires bridging multiple length scales (1m--1nm) and presents a true computational challenge.;In this thesis, we have followed a systematic approach to develop a multiscale modeling framework for fiber spinning. We first developed and validated the performance of a new computationally efficient, quantitatively reliable lattice-Monte Carlo method based on a novel lattice-subdivision technique in 2-dimensional lattices for modeling polymer chains in dense polymeric systems. The excellent performance of the 2-D Monte Carlo scheme with reliable estimates of the error motivated the 3-dimensional extension of the Monte Carlo algorithm. Alternatively, a new computationally cheap 3-segment mean-field model was also developed and its performance was compared against the more accurate Monte Carlo simulations. Although the mean-field model showed good performance far away from interfaces, it failed to capture any interfacial phenomenon, as seen in semicrystalline polymers, due to its inability to handle excluded volume effects.;The lattice-Monte Carlo method was then adapted in a novel two-tier hierarchical modeling framework for polymer fiber spinning, to suitably handle the nonequilibrium flow effects. Large scale parallel simulations in a parallel tempering scheme were performed at a wide range of flow parameters for homogeneous uniaxial extensional flow geometry, investigating the effect on three different microscopic morphologies: bulk amorphous, lamellar semicrystalline and fibrillar. In all the three cases it was seen that with an increase in the strength of the flow there occurs a sudden transition in the amorphous regions, from a disordered state to a relatively ordered one. A preliminary analysis of the extended free energies of different morphologies revealed that under relatively quiescent conditions the lamellar semicrystalline morphology is the thermodynamically favored one, while at higher deformation rates, the fibrillar structure seems to be thermodynamically most favored. This is in agreement with the experimental observations made in connection with many high-speed fiber spinning processes. |
