Molecular mechanisms of deformation of aligned polyethylene
File(s)
Author(s)
Hammad, Ali
Type
Thesis
Abstract
This study investigated how aligned polyethylene transforms as a system. The aim was to identify the relative strength of symmetry and antisymmetry in the system. An empirical framework was developed based on the Lennard-Jones potential, which included three nested algorithms. These nested algorithms provided a context specific empirical study of aligned polyethylene. The first algorithm enabled the formation of a soliton in a classical structure, in order to minimise the energy of the system. This provided indicative results, which suggest that solitons may transfer load from one molecular chain to another. The correspondence between the formation of solitons and the restoring force on chain ends was also examined. The second algorithm included the classical formation of a soliton into a statistical structure, in order to examine the behaviour of the soliton. The algorithm showed that there are two distinct timescales associated with the structure of the soliton. The coarse-graining of the temporal structure of the system, followed by subsequent fine-graining, showed the splitting of the soliton into +/- π/2 twistons. The third algorithm included the behaviour of the soliton within a geometric construction consisting of hexagonal sites, to examine how spontaneous symmetry breaking and symmetry restoration may occur in a system that is at the critical point of orthorhombic and hexagonal symmetry. It was found that the system behaves neither as a pure solid crystal nor as a pure fluid. Therefore it may be predicted that the system has connection to a liquid crystal, which may inform novel efforts in the future to transform not just aligned polyethylene but also other similar materials.
Version
Open Access
Date Issued
2015-12
Date Awarded
2016-08
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Sutton, A. P.
Iannucci, L.
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/G036888/1
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)