Solubilisation of dyes by surfactant micelles. Part 3; A spectroscopic study of azo dyes in surfactant solutions†

Abstract

A spectroscopic study (UV–vis and adsorption) has been made of the interactions of select model azo dyes with a range of surfactant types or their mixtures both above and below their respective critical micelle concentrations. All surfactants inhibit adsorption of the dyes to cotton above their critical micelle concentrations due to incorporation in micelles. However, formation of 1;1 complexes between dyes and cationic or zwitterionic surfactants in sub‐micellar regions results in enhanced deposition on cotton. It is shown that attractive or repulsive electrostatic interactions play a key role in dye binding to micelles. Unusually, spectra of complexes formed between the dye and cationic surfactant are typical of those of the azo tautomeric form as opposed to the hydrazone form that is prevalent in aqueous media. Addition of anionic surfactant to micellar solutions of nonionic or zwitterionic surfactants results in successive displacement of dye from the respective micelles, i.e. binding is competitive.

Adsorption of dyes to cotton and inhibition by surfactants, polymers and surfactant–polymer mixtures

“…The efficacy of the cationic and zwitterionic surfactants in inhibiting adsorption is consistent with earlier findings that electrostatic interactions play a key role in binding [3]. That the zwitterionic surfactant is more effective than the cationic surfactant is also consistent with earlier studies; its lower CMC means that the solution is richer in micelles [2,3]. As these dyes are larger and contain many more sulphonate groups compared to earlier studies, the implication is that these dyes bind at the surface of micelles, with the sulphonate groups forming multi-anchor points with oppositely charged micellar groups.…”

“…The zwitterionic surfactant has a modest influence on dye binding, particularly evident with the model dye (Figure 9a). Nonionic surfactant at submicellar levels is ineffective at competing with polymer for the dye; however, at micellar concentrations nonionic surfactant can augment polymer [3].…”

“…Earlier papers in this series focused upon the interactions of a specially synthesised series of substituted model azo dyes with: (i) anionic, nonionic, zwitterionic and cationic surfactants in both micellar and sub-micellar regions [1][2][3]; and (ii) non-ionic, zwitterionic and cationic polymers [4,5]. The zwitterionic surfactant was found to be most effective in binding model dyes; key factors were its low critical micelle concentration (CMC) and electrostatic interactions.…”

Potentiometric study of cetylpyridinium chloride cooperative binding to anionic azo-dyes

“…[5][6][7][8][9][10][11][12][13][14] In recent years these interactions have been studied, mostly spectroscopically. 4,10,12 These researchers have detected spectral changes of ionic dyes when the oppositely-charged or nonionic surfactants are added to aqueous dye solutions. The change in absorption band accompanied by the change of the color of the dye can be explained as the result of dye-surfactant interactions.…”

Solubilisation of dyes by surfactant micelles. Part 4: Influence of dye fixatives

“…Previous studies have reported fundamental molecular interactions between dyes and surfactants in solution [1][2][3]. An understanding of such interactions is valuable in understanding the role played by surfactants in modern domestic laundering, in particular the transfer of dyes from coloured fabrics to white materials.…”