The Behaviour of Dyes in Aqueous Solutions. Part I – The Influence of Chemical Structure on Dye Aggregation – A Polarographic Study

Polarography has been used to measure the extent of aggregation of a number of monazo acid dyes in aqueous solution. The effects of increasing hydrophobic character and the number and position of the hydrophilic sulphonate groups have been investigated. Increasing length of alkyl chain promotes aggregation particularly when this reaches four carbon atoms. The effect of increasing degree of sulphonation depends upon the positions in the dye molecule into which additional groups are introduced. The state of aggregation could not be completely explained in terms of a simple monomer-dimer equilibrium