Aggregation of Azo Dyes with Cationic Amphiphiles at Low Concentrations in Aqueous Solution

Abstract

The aggregation of a series of n-alkyltrimethylammonium bromide (C n TAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (C m pyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in the spectra of the dyes. Precipitates formed in aqueous solutions from the cationic surfactants and MO and pMR are C n TA−MO, C n TA−pMR, and C m py−MO salts and consist of an equimolar ratio of surfactant and dye. In similar experiments with EO, MR, MY, or ABS as the solvatochromic dye molecules, no precipitation occurred, although surfactant−EO salts precipitated at high EO concentration. Dye−surfactant salts formed from C n TAB and MO were found to form myelins in phase penetration experiments. Temperatures at which myelins start to form increase upon increasing alkyl chain length of the surfactant as revealed by optical microscopy. The formation of vesicles from C10TA−MO and from C12TA−MO crystals was indicated by electron microscopy. The presence and position of the ionic group in the dye molecule is important in determining the association. The importance of hydrophobic interactions is revealed by the chain length dependence on the aggregation process and the observation that interactions are absent in ethanol. Electrostatic interactions also play an important role, as shown by the effect of NaCl on the binding process.

Interactions of gemini cationic surfactants with anionic azo dyes and their inhibited effects on dyeability of cotton fabric

“…The nature of spacers has also a large influence on the aggregation of geminis. But, it has been reported that the spacer length hardly affects dyeesurfactant aggregation for 12-s-12, s Z 4,8,12 [5]. Regardless of the effect of different pH and measuring method, it can be concluded that in geminis with two methylene groups in their spacer, the aggregation with anionic dyes such as MO is higher than in other species.…”

“…In the case of 12-s-12 geminis, short spacers (s Z 2,3) induce the formation of wormlike micelles; geminis with intermediate spacers (s Z 4e12) form spheroidal micelles and vesicles are formed when s Z 16,20 [5]. hypsochromic shift which is about 45e55 nm is in the presence of DTAB.…”

“…So, the hydrophobicity increase of the surfactant or the dye, increases the binding energy [8]. It has been reported that the type of head group of surfactants has no large influence on the aggregation process [5,6].…”

“…There are strong indications that the dye molecules are arranged in a parallel way (H-type aggregation). It means the complex is a monomer involving electrostatic interaction between the positive charge of cationic surfactant and negatively charged sulphonate group, with the alkyl chain of cationic surfactant in close contact with the rest of the dye molecule and, particularly, the azo group (the chromophoric unit)[5,14]. Some of these complexes can aggregate and precipitate in the solution which is in equilibrium with the precipitates.…”

Synthesis and Surface Active Properties of Gemini Cationic Surfactants and Interaction with Anionic Azo Dye (AR52)

“…Surfactants are used as auxiliaries in most textile finishing processes such as washing, wetting, dispersing, dyeing and finishing. Also, the interaction between dyes and surfactants have been studied to provide some insight into small molecule-macromolecule interactions, which is of major importance in biochemistry [14].…”