published_or_final_version / Electrical Engineering / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

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In the past decade, electrostatic layer-by-layer (LBL) assembly has gained attention because it is a facile and robust method to prepare thin polymer films. Due to the industrial importance and natural abundance of cellulose, its incorporation into LBL films is of particular interest. This thesis examines the use of nanocrystalline cellulose, prepared by sulfuric acid hydrolysis of cotton, in polyelectrolyte multilayer films. Conventional solution-dipping and a spin-coating variant of LBL assembly both resulted in chemically defined, reproducible, and smooth films with adjustable properties. Surface morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was monitored by X-ray photoelectron spectroscopy (XPS) and optical techniques. Orientation of the rod-like cellulose nanocrystals imparted anisotropic film properties, and birefringence was calculated from angle dependent and wavelength dependent optical reflectometry measurements. While spin-coating resulted in radial orientation of the nanocrystals, electrostatic adsorption in a magnetic field led to linear alignment. The internal structure, surface orientation and wettability of these materials were investigated. The attractive and repulsive forces acting close to the surface of the multilayer films in aqueous media were measured by colloid-probe AFM and the interaction forces between the film surfaces and charged colloidal-probes were compared to the predictions of the DLVO theory. The applications and advantages of polyelectrolyte multilayers containing nanocrystalline cellulose and their potential as model cellulose surfaces are discussed.

This thesis investigates the application of low energy electron irradiation to 1,3,5-trimethylbenzene films to test whether site-selective C–H bond cleavage can be achieved in a molecule presenting both aliphatic and aromatic target sites. IRRAS was used to characterize the orientation of vapour-deposited 1,3,5-trimethylbenzene on Au(111) and alkanethiolated gold under UHV and cryogenic conditions. On both substrates, the disordered as-deposited films were transformed by thermal treatment, producing two film structures – within the first 4-monolayers, aromatic rings lie nearly parallel to the metal surface, while molecules in additional layers are more upright. Low energy electron irradiation (0-10 eV) produced no dissociations in 1,3,5-trimethylbenzene; however, low energy electron transmission spectra indicate charge accumulates at interstitial sites in the mesitylene film, decelerating subsequent incident electrons. These decelerated electrons traverse the charged film and are reaccelerated, inducing dissociations in the underlying SAM. Contrary to literature claims, 1,3,5-trimethylbezene is a poor molecule for adsorption studies such as BET as the initial adsorption is disordered and thermodynamically unstable.

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