Studies in the physical state of dyestuffs

Shah, Navinchandra Bhogilal (1965) Studies in the physical state of dyestuffs. MSc(R) thesis, University of Glasgow.

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The first part of this thesis deals with a statistical survey of the colour Index data or fastness properties of dyes and its relation to their molecular constitution. Both washfastness and resistance to migration of a groan of acid dyes on wool rise directly with the molecular weight of the dye. Chrome mordant dyes, which may be regarded as forming 1,1 - or 2,1 - dye met complex on the wool fibre, also display a similar tread. This may be attributed either to an increase in moleoular weight by the formation of the dye-metal complex, or to the formation of firmer dye-fibre bonds through chelation with chromium. Various attempts were made to correlate light-fastness with washfastness of acid dyes on wool and of direct dyes on cotton, but the results were not significant. There is, however, a relation between lightfastness and anionic weight for a group of acid dyes. There is an inverse relation between molecular axial ratio and lightfastress of arthraquinone vat dyes or cotton; lightfastness decreases with increase in the ratio of molecular length to width. The molecular geometry o acid and direct dyes does not vary enough for significant trends trends to be revealed. There is, however, a significant correlation between molecular axial ratio aid the proportion of fading caused by the visible spectral region (McLaren's data). Both these results are attributed to the formation of more stable aggregates with decrease in molecular axial ratio, though the result may be influenced chemical factors. The second part of the thesis deals with studies in the association of dyes at inorganic surfaces. Theories of solution adsorption have been applied to interpret the adsorption results. The concept of 'coverage factor' has been fully developed and a direct relation between (log10) coverage and (log10) ionic weight of fully conjugated dyes has been found. This relation may be used to find the suitability of a dye for specific surface area measurement. Unconjugated or imperfectly conjugated dyes do not appear to obey the relation. r empirical approach has, however, been sought to fit them to the relation and it has been how, that the size of the micelles may be governed by the average size of the individual conjugated systems in a dye molecule. These experiments have revealed that "coated" titania. (i.e. titania treated in manufacture with silica and (v) and alumina) appears to lose its surface area and its hydrogen bonding capacity for some dyes, or ageing at room temperature. Uncoated titania does rot do so. Furthermore the ageing effect on coated titania appears to be partly reversible and a port of the lost surface area can be recovered or heath r the sample. Basic triphenylmethane dyes display an endothermic adsorption effect on alumina. This anomalous effect has been explained on the basis of the theory of resonance. The amount of a dye adsorbed at room temperature is governed by its ionic weight, but at higher temperature it may be governed by the Lumber of resonating forms by which it car be represented. The aggregates of dye molecules formed on the substrate surface at a higher temperature are supposed to he of different structure from those formed at room temperature. It is attested that at higher temperatures the reaggregation of dye molecules or the substrate surface occurs so as to reduce the free energy to a minimum. This favours the building up of larger and more stable aggregates.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: C H Giles
Keywords: Textile research
Date of Award: 1965
Depositing User: Enlighten Team
Unique ID: glathesis:1965-72185
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 12:37
Last Modified: 17 May 2019 12:37

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