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Title: Studies in monolayer adsorption
Author: Cameron, Angus
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1957
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The spreading properties of various sulphonated dyes containing alkyl chains have been studied, in monolayers on water. It is found that when spread on water partial or complete solution of the monolayer occurs. On decreasing the solubility of the dyes, however, by spreading on concentrated solutions of inorganic salts condensed films are obtained for all dyes with a chain length of 12 carbons or over. Dyes containing short alkyl chains (i.e. C4 and under) generally do not form surface films, though with the larger sized molecules gaseous films are formed. Mixing of cetyltrimethy lammonium brouide with the before spreading causes most of the short chain dyes, which do not form monolayers by themselves, to form a stable mixed film. It has been found that dyes which are surface-active (i.e. those dyes which form films without the aid of cetyltrimethylammonium bromide) are often less fast to light than non-surface active dyes. The inference is that the dyes which form stable monolayers at the air-liquid interface also form monolayers when ads bed on a substrate. Those dyes which do not form surface films, on the other hand, are believed to form a gregates in the substrate. The monolayer-forming dyes then expose a much larger solid-to-air surface in the substrate, resulting in a decrease in light fastness. Thus the light fastness of a series of dyes depends to some extent upon their surface activity; those which form monolayers are often the most fugitive. Cetyl acetate and methyl- and ethylstearyl ketones have been spread on aqueous solutions of various solutes. It is found that large dye molecules and medium-sized bifunetional molecules expand films of cetyl acetate, whereas the ketone films remain relatively unaffected. The dyes are believed to be bonded by both Van der Waals and polar forces whereas the bifunctional molecules are bonded mainly by polar forces and each molecule cross-links two film molecules. Cellulose triacetate films have also been studied. It is believed that when these are spread on water incomplete breakdown of the micelles occurs and aggregates as well as a monolayer are formed. The dyes are found to expand these partially spread films, and it is believed that the dyes have sufficient affinity to form comletes with the monolayer, but not enough to penetrate the micelles or aggregates by breaking the inter-chain bonds. Substances which are strongly bonded to cellulose triacetate, e.g. urea, can penetrate the micelles by breaking interchain bonds therein. The attachment of the non-ionic so-called 'disperse' dyes to cellulose triacetate has been studied by similar methods. A typical dye of this class, which is readily adsorbed by cellulose triacetate, when mixed with cellulose triacetate and spread as a mixed film gives no increase in the area of the film. It is suggested that the dye is oriented along the underside of the polymeric chains by polar and perhaps also by non-polar attraction. The effect of dyes on protein films was next studied. Acid dyes in acid solution expand these films but the expansion decreases with increase in pH and at pH 7.0 it approaches zero. These results were compared with the known adsorption properties of these dyes on wool, and it was found that the effect of pH is similar in both cases.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available