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Title: Studies of the binding strengths and modes of action of organic ligands on aluminium trihydroxide surfaces
Author: Robertson, Johanna H.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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This thesis describes work aimed at identifying new treatments for aluminium(oxide) surfaces which are based on complex formation at the interface by relatively simple organic ligands. Such an approach offers a more benign alternative to the surface roughening or passivation by strongly acidic and/or oxidising treatments which are currently used commercially. A specific objective of interest to the organisation sponsoring the work (Alcan) was the development of new dispersants for aluminium trihydroxide (ATH) which is used as a flame retardant in organic polymers. On the basis of reports of earlier work undertaken in Zeneca Specialities polyphenolic ligands were selected as candidates for the ligating headgroups. The synthesis of a series of esters of gallic acid (3, 4, 5-trihydroxybenzoic acid) with varying lengths of alkyl group tails is reported in Chapter 2 together with an investigation of their strength of binding to high surface area ATH (superfine grade) by monitoring the uptake by uv-spectrometry from 95% methanol/water. Analysis of results based on Langmuir adsorption isotherm behaviour confirms the suitability of pyrogallol-based ligands for ATH since all of the ligands exhibit very strong binding. The tail group contributes in no part to the binding efficiencies. Furthermore, no insight into binding modes can be inferred from isotherm results and no differentiation can be made between the binding strengths of closely related ligands. In an attempt to understand the modes of attachment, integrated use of experimental adsorption isotherm results and molecular modelling techniques have been used in Chapter 3. Additional classes of ligands involving dihydroxybenzene and 3-methyl-4,5-dihydroxybenzene headgroups were synthesised and tested. The approach involves simulating the chemisorption of a monolayer of the organic ligand onto the aluminium metal oxide surface. The results suggest that the stabilites and structures of the interfacial complexes depend not only on metal-ligand coordinate bonds, but also on secondary bonding interactions. Trihydroxybenzene headgroups bind more strongly than dihydroxy which bind much more strongly than monohydroxy headgroups.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available