Studies on Monolayers

Neustadter, E. L (1952) Studies on Monolayers. PhD thesis, University of Glasgow.

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As a preliminary to the ultimate photochemical study of monolayers, aromatic azo-compounds (with one hydroxy-group either o- or p- to the azo-group in most cases) quinones, acid amides and a hydroquinone derivative have been examined for monomolecular film-forming properties on water by means of the Langmuir film balance. The largest group of compounds examined was that of the azo-compounds. These are found to form condensed films in all cases where a hydroxy-group is present and the alkyl chain has at least 16 C atoms; and also in many cases where the chain has only 12 C atoms. In absence of a hydroxy-group, at least two azo-groups appear to be required to give the necessary water attraction for film formation. The molecules appear to be oriented in the film with the plane of the aromatic nuclei vertical but the longer axis of this plane is in many cases tilted from the perpendicular at an angle depending on the nature and relative position of the various substituent groups. The azo-group appears to be at or near the water surface in all cases. The orientations of the other compounds were also studied and it was found the angles of orientation to the water surface seem to lie between 40 and 90. The tautomeric equilibrium of azo-compounds in monolayers has been studied by determining their apparent molecular areas and compressibilities on dilute acid and alkali. In accordance with published data, the p-hydroxy compounds appear to exist almost completely in the azo-form. The o-compounds contain much of the hydrazone form but the results do not give decisive evidence of the presence or absence of the azo-tautomer in this series, except in one case where an o:o'-dihydroxyazo-compound appears to contain the azo-form. One purpose of the work being the study of the photochemical decompositions of azo-compounds, which is believed to result in the formation of phenols, selected azo-compounds were examined by the film balance technique using solutions of various phenolic substances as substrates in place of water. By this means, azo-, hydroxy-, and quinone groups in monolayers of aromatic compounds were found to form hydrogen bonds with the hydroxy-groups in phenols. The increased water attraction imparted thus, e.g., to the azo-group, may cause an expansion of the film by a change in the angle of tilt of the molecules therein. Dihydric phenols in the substrate appear to behave in two ways: (a) If there are two suitably placed bonding groups in the monolayer molecule, a 1:1-complex may be formed, in which each group is bonded with one hydroxy-group in the solute molecule; two molecules probably stand parallel side by side and the area of the film increases slightly. (b) If the solute hydroxy-groups are too far apart for (a) to occur they may form cross-links between monolayer molecules leading/ leading to a considerable increase in film area and compressibility. These experiments were extended in order to study the combination between dyes and fibres, e.g., proteins, acetate rayon and cellulose, by the use of "model" compounds in the substrate. The hydrogen bond is found here to be of great importance, as has previously been suggested. In several cases the dependence of hydrogen bonding power on pH was demonstrated. Preliminary fading experiments were performed on azo-dye monolayers and other substances. These showed that fading in monolayers is slow and that powerful light sources will have to be employed for significant results to be obtained. A surface potential measuring apparatus was also constructed for future work on the irradiation of monolayers.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1952
Depositing User: Enlighten Team
Unique ID: glathesis:1952-78917
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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