Liquid crystalline thennosets (Lt.Ts) are a special class of materials which generated significant interest since they demonstrated the combination of the anisotropic physical properties of the mesophase and the specific properties of thennosets. Among them, the water barrier property of LeTs makes them very promismg materials for the potential applications in electronics and coatings. Liquid crystalline monomer, 4, 4'-diglycidyloxy-a-methylstilbene (DOMS), was synthesized and cured with different crosslinking agents, such as sulphanilamide, diaminodiphenylsulfone, diaminodiphenylmethane, and 2,4-Diaminotoluene. LeTs with different liquid crystalline structures were produced and their structural, dynamic mechanical and permeability properties are characterised. The conventional epoxy monomer, diglycidyl ether of bisphenol-A (BADGE) is also involved in our study and resins formed by BADGE and curing agents are used as comparisons to the DOMS LeT systems. Polarized optical microscopic tests were used to form time-temperature-transition (TTT) diagrams for different systems, which provide important information about the curing process of Lf.Ts. Relationships between curing conditions, structure and properties are created by TTT diagrams and microscopic observations. Differential scanning calorimetry and wide angle X-ray scattering tests demonstrated the typical smectic features of LeTs systems. In the dynamic vapour sorption tests, the extraordinary water barrier property of smectic LeT is revealed. The water permeability of LeT was reduced by 74.6% at 65 'C and by 63.7% at 85'C in comparison with the conventional thermoset. Smectic Le structure was proven useful in reducing the water permeation in epoxy thennosets. Dynamic mechanical analysis combined with computer modelling was employed to investigate the correlation between water permeation and inner structure of materials to clarify the mechanism of moisture diffusion and sorption in LCTs. The information and results obtained in this work would be of great importance for the potential industrial applications of LeTs. - i -
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:574560 |
| Date | January 2011 |
| Creators | Nie, Lei |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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