Thesis

PU elastomers and grafted GO/PU nanocomposite with self-healing and self-adapting capabilities for next-generation electrical insulation

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16956
Person Identifier (Local)
  • 201977395
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • The demand for next-generation dielectric materials with substantially improved reliability is spurred by the development of global energy industry, where extremely harsh operating environment for electrical and electronic materials and increasingly complex insulation system are present. In order to solve the problem of local electric field distortion and electrical damage of insulating materials in high-voltage electrical equipment, the development of a dielectric material with simultaneous self-healing and self-adaptive electrical properties is an enabling material to achieve this goal but has not yet been realised. In this study, the structure-activity relationship between the microphase-separated structure and the electrical properties of polyurethane elastomers (PUs) is clarified by investigating the morphology, chemical, and electronic structure of PUs with respect to their macroscopic insulating properties. Self-healing capability of electrical damage in PUs with high dielectric strength was achieved using reversible hydrogen bonding network and shape memory effect. By further grafting two dimensional graphene oxide (GO) nanosheets as the conductive backbone and regulating the concentration of nanoparticles and their interfacial states, it was shown that the GO/PU composites have excellent nonlinear response while retaining the self-healing capability, which has an excellent potential to be developed into a new generation of smart insulating materials. Firstly, the structure-activity relationship of PU elastomers is investigated comprehensively utilising quantum chemical simulation, chemical-physical structure characterisation and molecular relaxation behaviour to instruct the preparation of the desire PU materials. As a result of the inconsistency in the energy levels of the molecular orbitals between the internal soft segments (SS) and hard segments (HS), the microphase-separated PU possesses a deeper energy barrier between the SS and HS interfaces, which significantly enhances the insulating performance of the material. Subsequently, the reversible hydrogen bonding network and shape memory effect of the screened PU with robust dielectric strength are verified by variable temperature infrared spectrum and calculated conformation entropy, respectively, which are the main driving forces to achieve the self-healing function. 2D optical micrographs, 3D computed micro-X-ray tomography, and cross-sectional SEM images all confirmed that the micro dendritic defects in the designed PU are completely healed under moderate thermal stimulation, while restoring its insulating strength evaluated by the maximum discharge amplitude (Qm) of the partial discharge. Additionally, isocyanate grafted GO nanosheets are introduced into the self-healing PU matrix with the purpose of enabling the nanocomposite to acquire self-adaptive capabilities. The nanocomposite with a 5% volume fraction of GO exhibits superior nonlinear electrical behaviour with a switching field strength of 0.7 kV/mm, a nonlinear coefficient of 4.7, which are much better than those of traditional GO blended composites with a switching field strength of 8.5 kV/mm, a nonlinear coefficient of 2.3. The significantly improved nonlinear characteristic including the switching field strength and the nonlinear coefficient of the grafted nanocomposite is mainly attributed to the tailored interface between GO and PU matrix with considerably lowered interfacial energy barrier, as confirmed by quantum chemical calculations, nanoscale Kelvin probe force microscopy (KPFM) and macroscopic thermally stimulated current. The application of this grafted GO/PU nanocomposite exhibited excellent self-adaptive field grading capability at typical triple junction with field distortion. The grafted GO/PU nanocomposites reveal repeatable self-healing capabilities under the stimulation both of light irradiation and heating, involving the recovery of its novel nonlinear electrical properties and structural restoration. This versatile grafted GO/PU nanocomposite is expected to be promising for next-generation electrical insulation.
Advisor / supervisor
  • Liggat, John J.
  • Given, Martin J.
  • Siew, Wah Hoon
Resource Type
DOI
Date Created
  • 2023

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