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Title: Sum-frequency spectroscopy of monolayers adsorbed on hydrophobic and hydrophilic solid substrates
Author: Briggs, A. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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The technique of infrared-visible sum-frequency spectroscopy (SFS) has been used to investigate surfactants and self-assembled monolayers (SAMs) adsorbed on solid surfaces. In Chapter 1, the technique of SFS is introduced in terms of its general application and theory with comparisons drawn to other interface sensitive techniques. The experimental methodology and analytical approach are described in Chapter 2. While references are made to surfactants in Chapters 1 and 2, discussion of surfactant behaviour per-se is postponed until Chapter 3. In this chapter, in-situ investigations of surfactant adsorption from aqueous solution onto model hydrophobic substrates of octadecanethiol (ODT) are detailed. The focus is on the behaviour of novel sugar-based surfactants as a function of chain length, solution concentration and temperature. Monolayers of decanol and DDAB are studied at the same interface by way of comparison. Chapter 4 is the central chapter in terms of technique development, describing the extension of SES to monolayers on hydrophilic surfaces, principally mica. A novel experimental configuration is employed where the mica is back-coated with gold. This variant of SFS has been called the displaced metal surface or DIMS method to highlight the fact that interpretation requires careful consideration of the mica thickness. SAMs formed from octadecyltrichloro-silane (OTS) are used to aid the development of the DIMS method. The self-assembly process is then investigated for alkylsilanes with focus on reproducibility in monolayer preparation and water stability. OTS was also adsorbed directly on bare gold and studied by conventional SFS, highlighting the insensitivity of monolayer structure to the type of hydrophilic substrate and serving as a reference for the DIMS spectra. In Chapter 5, feasibility studies are described using SFS in non-aqueous environments. The solid/toluene interface is probed by DIMS SFS using an OTS monolayer, and by conventional SFS using a partially fluorinated substrate. Deuterated toluene was used in this work to allow transmission of the IR beam.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available