Study of the Dynamics of Glass Forming Liquids Using Molecular Dynamics Simulations

Open Access
Author:
Sokolowski, Christopher Henry
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Janna Kay Maranas, Thesis Supervisor
  • Themis Matsoukas, Honors Advisor
Keywords:
  • molecular dynamics
  • torsion
  • non-bonded
  • interactions
  • glass transition
  • strong
  • weak
  • glass
Abstract:
The process that occurs as a glassy polymer transitions into an amorphous polymer is currently not well understood. In these materials, two distinct relaxation processes are observed: one of which is related to the glass transition and the other that is not. Previous research has hinted that if the strength of non-bonded interactions between atoms is increased, the relaxation times of the material respond like the relaxation process related to the glass transition, whereas if the torsional barriers of molecules are increased, the relaxation times respond like a completely different process unrelated to the glass transition. This connection of physical process like glass transition with relaxation behavior has not been clearly made. This experiment explored how different combinations of strengths of non-bonded and torsional forces affected the relation processes of the materials. We have found that for simulations with non-bonded forces greater than two times chemically realistic values, the polymer transitioned from a fragile to a strong glass. This transition from a fragile to a strong glass with increasing non-bonded interaction strength implies that non-bonded interactions are responsible for this fragile to strong transition, which is important because the mechanics behind this transition currently are not understood well. We have also found that Boland’s hypothesis holds true for the fragile glasses, and that changing non-bonded interactions and torsional barriers for fragile glasses results in the same effects on molecular behavior (via the diffusion coefficient) and segmental behavior (by the characteristic decay time). More research needs to be conducted investigating the effect of non-bonded interactions on the transition from fragile to strong glasses in order to investigate the mechanics behind the process.