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Title: Molecular mechanisms of deformation of aligned polyethylene
Author: Hammad, Ali
ISNI:       0000 0004 7233 128X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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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.
Supervisor: Sutton, A. P. ; Iannucci, L. Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral