Date of Award
Ph.D. in Engineering Science
In this dissertation, lower length scale phenomena associated with the responses of hybrid materials to harsh and extreme environments were studied. The goal of this research was to reveal the underlying mechanisms of damage mitigation in these materials and the role that interface, and relevant material component interactions play in the overall material response. First, the thermal decomposition behavior of a technologically important material system, i.e., pristine graphene (PG) and graphene oxide (GO) reinforced poly(ethylene oxide) (PEO), was investigated using a reactive molecular dynamics simulation methodology. The simulations were performed in both non-isothermal (dynamic gravimetric) and isothermal modes of decomposition. Overall, the introduction of PG to the PEO system improves the thermal stability of the polymer in both decomposition modes. A delay in the temperature of the onset of decomposition in the non-isothermal mode and a nearly 60% increase in the activation energy of decomposition in the isothermal mode is observed for the PEO-PG system. This effect gets more pronounced with an increase in the PG concentration in the system. In contrast, introducing GO in the PEO system deteriorates the thermal stability of the polymer, even though, similar to the PG concentration effect, the thermal stability of the polymer is increased with increasing GO concentration. Second, the effect of surface modification of polyoctahedral silsesquioxane (POSS) and its concentration in a polyimide (PI) matrix, as well as the effect of nanoparticle type (POSS, graphene, and carbon nanotube (CNT)) and the nanoparticle orientation in Gr and CNT nanoparticles in the PI matrix exposed to atomic oxygen (AO) bombardment were studied using a reactive molecular dynamics simulation methodology. Among all systems, PI with randomly oriented CNTs or Gr nanoparticles gave, in general, the lowest mass loss, erosion yield, surface damage, AO penetration depth, and temperature. Grafting of the POSS nanoparticles with PI and the increasing the PI concentration lowers the erosion yield of the PI-POSS systems, with the effect of former being greater on the AO damage mitigation. The results of this fundamental study shed light on the lower length scale phenomena associated with AO damage mitigation in different PI-nanoparticle systems. Third, the through-thickness temperature distribution and thermal conductivities of unprotected neat crosslinked epoxy, and protected epoxy/graphene, and epoxy/montmorillonite/graphene systems were investigated against lightning strike damage. It was inferred that the montmorillonite/graphene top coating has great potential to be used as a lightning strike damage protection measure for epoxy-based composite systems. A more thorough multi-physics (electrothermal) analysis of the montmorillonite/graphene system may further reveal its lightning strike damage mitigation efficiency.
Rahmani, Farzin, "Molecular Dynamics Simulation Of Polymer Nanocomposites In Extreme Environments" (2018). Electronic Theses and Dissertations. 403.
Emphasis: Chemical Engineering