| Popis: |
The main goal of this dissertation is to develop a simulation methodology to investigate the thermodynamic and structural behavior of a polymer in a crystallizable solvent. In addition to the polymer chain in a crystallizable solvent, two other models are analyzed, including the monodispersed and polydispersed solvent configurations. The study of the monodispersed solvent is motivated by a recent publication that employed a hybrid technique utilizing both Molecular Dynamics (MD) and Wang-Landau (W-L) Monte Carlo (MC) in order to determine the solid-liquid equilibrium of Lennard-Jones (LJ) spheres. In this work, the hybrid method is modified by replacing the W-L MC method with a new MC scheme. It is found that there is a first order phase transition due to a discontinuity in both the entropy and volume as a function of temperature and pressure. Moreover, based on the simulation results, the crystalline state of the solvent displayed a face-centered cubic (FCC) symmetry. This model is then extended by introducing varying degrees of polydispersity into the solvent. The first order phase transition observed in the monodispersed solvent disappears due to the imperfect packing in these systems, causing the formation of an amorphous solid state. Specifically, as the width of the atom sphere size distribution is increased, there is a significant reduction in the crystalline order. Next, the monodispersed solvent model is modified by placing a polymer chain in the solvent. In order to sample different chain conformations in the crystalline solvent, a new reptation move for the polymer chain is developed. The introduction of this chain did not disrupt the crystalline order in the system, thus enabling a first order phase transition to be observed. However, compared to the monodispersed spheres model, this transition disappears at high pressures due to the different responses of the various inter-atomic potentials to compression. The FCC symmetry of this system is enhanced due to the co-crystallization of the polymer with the solvent. There is more crystalline order in this model compared to the monodispersed solvent because the atom distance ranges have been restricted by the chain bonding potential. |
