Masaru Mitsuishi

Effects of hydrating water molecules on the aggregation behavior of azo dyes in aqueous solutions

Abstract The aggregation behavior of three sulfonated monoazo dyes (C.I. Acid Red 88, C.I. Acid Red 13 and C.I. Acid Red 27) was investigated by means of visible absorption spectroscopy to elucidate the effects of the sulfonate groups. The aggregation numbers of the three dyes were estimated as two. The aggregation constant K Agg of the dye containing two sulfonate groups was the largest. This result is inconsistent with that expected from the electrostatic repulsion between the sulfonate groups in the dyes, suggesting that the other effects are dominant. The thermodynamic parameters determined from the temperature dependence of K Agg indicates that Hydrophobie interaction is involved in the aggregation reaction. From this, it is concluded that the hydrating water molecules around the dyes play an important role in the aggregation process. Furthermore, the effects of urea were investigated to clarify the influence of cosolutes on the aggregation behavior.

Aggregation behaviour of an azo dye containing a trifluoromethyl group on poly(vinylpyrrolidone)

The aggregation behaviour of an azo dye containing a trifluoromethyl group (p-FTS) in aqueous solutions has been investigated by means of visible absorption measurements. The thermodynamic parameters for aggregation were calculated from the dependence of the aggregation constants on temperature. The thermodynamic parameters for the corresponding dye containing a methyl group (p-TS) were different from those of p-FTS, suggesting that the fluorine atoms of the dye molecule affect its aggregation behaviour. To elucidate the effects of poly(vinylpyrrolidone), the binding constants of the dyes with the polymer were determined. Furthermore, considering the binding constants, the aggregation constants on the polymer chains were estimated. The thermodynamic parameters determined for the aggregation on the polymer chains were different from those for the aggregation in water, indicating that the aggregation mechanism on the polymer chains is different from that in water. From this result, some models of the dye aggregates are proposed.

Degradation of an azo dye by sodium hypochlorite in aqueous surfactant solutions

Abstract The degradation behaviour of sodium 1-(2-methylphenylazo)-2-hydroxy-3,6-naphthalenedisulphonate (o-TR) by sodium hypochlorite solution in the presence of three kinds of surfactants, viz. dodecytrimethylammonium bromide (DTAB), sodium dodecylsulphate (SDS), and sodium 2-(dodecylmethylamino)-ethane-1-sulphonate (SDAS) was investigated by means of visible absorption spectrum measurements. The degradation rate of o-TR was markedly dependent on the head groups of the surfactants. DTAB containing a quaternary ammonium head group significantly enhanced the degradation rate. SDS containing a sulphate head group enhanced the rate below the critical micelle concentration (CMC), whereas it did not change above CMC. SDAS containing a tertiary amino and suphonate group immediately degraded the dye existing outside of the micelle formed by SDAS, while the dye solubilized into the micelle remained without degradation.

New procedure to calculate the aggregation constants of dyes

Abstract A new procedure to calculate the aggregation constants of dyes is proposed. This procedure can determine not only the aggregation constants but also the extinction coefficients of dye monomers. It is therefore of particular value in the case of dyes which form aggregates even at low concentration. The aggregation constants for the dyes studied were calculated using the present procedure and compared with the previous values. From the results, factors pertinent to the estimation of the aggregation constants are discussed.

Effects of bolaform electrolytes on the interaction between a water-soluble polymer and sulphonated monoazo dyes: Part 2: Aromatic bolaform electrolytes

Abstract The effect of aromatic bolaform electrolytes which contain two quaternized amino groups and two phenyl rings on the interaction between sulphonated monoazo dyes and poly (vinylpyrrolidone) was investigated using visible absorption spectrum measurements. Since the aromatic bolaform electrolytes aggregated in a higher concentration range, the formation of complexes between the dyes and the bolaform electrolytes was investigated in the concentration range where no aggregate was formed. An equation based on the equilibria in the ternary systems containing the dyes, the bolaform electrolytes and poly (vinylpyrrolidone) was used to estimate the first binding constants of the dye/bolaform electrolyte complexes with poly (vinylpyrro-lidone); the values were smaller than those of the dyes themselves. The effect of the aromatic bolaform electrolytes on the interaction between the dyes and poly (vinylpyrrolidone) is discussed, as compared with that of aliphatic bolaform electrolytes, by using thermodynamic parameters calculated from the temperature dependence of the first binding constants.

THERMODYNAMIC STUDY OF THE AGGREGATION OF AZO DYES CONTAINING TWO TRIFLUOROMETHYL GROUPS IN AQUEOUS SOLUTIONS

The aggregation behaviour of azo dyes containing two trifluoromethyl groups, sodium 5-(3,5-bistrifluoromethyl-phenylazo)-6-hydroxynaphthalene-2-sulfonate, 1, and disodium 4-(3,5-bistrifluoromethylphenylazo)-3-hydroxy-naphthalene-2,7-disulfonate, 3, in aqueous solutions has been investigated by 19F NMR and visible absorption spectroscopy. The visible absorption spectra of the corresponding azo dyes containing two methyl groups, sodium 5-(3,5-dimethylphenylazo)-6-hydroxynaphthalene-2-sulfonate, 2, and disodium 4-(3,5-dimethylphenylazo)-3-hydroxynaphthalene-2,7-disulfonate, 4, in aqueous solutions have also been measured. From the visible absorption spectra, the aggregation number has been estimated to be 2 for all the dyes in the concentration region under examination (1 × 10–5 to 1 × 10–3 mol dm–3) and the aggregation constants have been calculated, the temperature dependence of which led to the determination of the thermodynamic parameters. Consequently, the substituents in the dyes affected entropically the aggregation processes. The aqueous solutions of 1 at concentrations greater than 5 × 10–3 mol dm–3 became gelatinous while those of 2, 3 and 4 did not. 19F NMR spectra have been recorded to elucidate the behaviour of 1 and 3 at the higher concentrations. The 19F NMR spectra of both dyes consisted of one singlet whose shapes did not change with dye concentration. The fluorine signals exhibited a progressive shift to higher and lower magnetic field with increasing dye concentration for 1 and 3, respectively. From this concentration dependence, the aggregation constants and the differences in the chemical shifts between the dye monomers and aggregates have been estimated. The aggregation constants determined by 19F NMR were in fair agreement with those calculated using visible absorption spectra. Furthermore, the differences in the chemical shifts between the dye monomers and aggregates have given important information concerning the relative spatial location between a fluorine atom and an adjacent aromatic ring.

Relationship between aggregation and degradation of an azo dye in aqueous solutions

Abstract The degradation behaviour of sodium 1-(2-methylphenylazo)-2-hydroxy-3,6-naphthalenedisulphonate (o-TR) by sodium hypochlorite solution in the presence of ionenes was investigated by means of visible absorption spectrum measurements. The degradation rate of o-TR markedly changed with the ionene concentration. The visible absorption spectra of the aqueous dye solutions in the presence of the ionenes were measured to clarify the situation of o-TR in the ionene solutions. It was found that dye o-TR aggregated in a solution with a certain ionene concentration, this concentration being consistent with the concentration at which the degradation rate became the slowest. It is therefore concluded that the degradation rate of the dye aggregate is significantly slower than that of the dye monomer.

Effects of bolaform electrolytes on the interaction between a water-soluble polymer and sulphonated monoazo dyes. Part 3: Dyes containing two naphthalene rings

Abstract The effects of bolaform electrolytes containing two quaternized amino groups on the interaction between poly(vinylpyrrolidone) and sulphonated monoazo dyes containing two naphthalene rings were investigated using visible absorption spectrum measurements. Several kinds of complex between the dye containing two sulphonate groups and an aromatic bolaform electrolyte were formed. The first binding constants of the dyes containing two naphthalene rings with the polymer were much larger than those of the dyes containing one benzene and one naphthalene ring. An equation based on the equilibria in the ternary systems containing the dyes, the bolaform electrolytes and poly(vinylpyrrolidone) was used to estimate the first binding constants of the dye/bolaform electrolyte complexes with the polymer. In the case of the dyes containing two naphthalene rings, aliphatic bolaform electrolytes enhanced the first binding constants just as in the case of the dyes having one benzene and one naphthalene ring. However, the degree of the enhancement for the former was much larger than that for the latter. The influence of the bolaform electrolytes on the thermodynamic parameters for the binding was dependent on the number of the sulphonate groups in the dyes. This is explained by the difference in the structure of the dye/bolaform electrolyte complexes formed.

Effects of bolaform electrolytes on the interaction between a water-soluble polymer and sulphonated monoazo dyes. Part 4: Dyes containing two sulphonate groups and aromatic bolaform electrolytes with different chain length of the spacer groups

Abstract The effects of aromatic bolaform electrolytes containing two quaternized amino groups, two phenyl groups and different chain lengths of the spacer groups on the interaction between poly(vinylpyrrolidone) and sulphonated monoazo dyes containing two sulphonate groups were investigated using visible absorption spectrum measurements. Several kinds of complexes between the dye containing two sulphonate groups and aromatic bolaform electrolytes could be formed, with dye:bolyte ratios of 1:1 or 1:2. The 1:2 complex is, however, not likely to be formed due to steric hindrance and its low solubility, so that the preferential formation of the 1:1 complexes is assumed. The binding constants of the dye with the aromatic bolaform electrolytes calculated, under this assumption, were found to be dependent on the chain length of the spacer groups. Furthermore, the thermodynamic parameters for the binding were smallest when the number of carbon atoms in the spacer groups was six. This result can be explained by the structure of the complexes. An equation based on the equilibria in the ternary system containing the dyes, the bolaform electrolytes and poly(vinylpyrrolidone) was used to estimate the first binding constants of the dye/bolaform electrolyte complexes with the polymer. In all cases of the aromatic bolaform electrolytes, their addition reduced the binding constants of the dye with the polymer, but the manner of the reduction was dependent on the length of the spacer methylene chains.

Sorption behaviour of fluorinated azo sulphonated dyes by silk fibre

Abstract The sorption behaviour of sodium 1-phenylazo-2-hydroxy-6-naphthalenesulphonate and its derivatives containing a trifluoromethyl or methyl group by silk fibre under acidic conditions was investigated. For all the dyes the equilibrium sorption was established after the silk fibre was immersed in the aqueous dye solutions for 24 h. The sorption isotherms obtained were explained on the basis of the single Langmuir type sorption mechanism or the dual sorption mechanism formulated by the sum of Langmuir and partition type sorption. The number of binding sites for Langmuir type sorption was consistent with the content of amino groups in the silk fibre indicating the stoichiometric binding of the anionic dyes with the positively charged amino groups. The thermodynamic parameters calculated from the temperature dependence of the intrinsic binding constants for Langmuir type sorption were greatly affected by the introduction of a trifluoromethyl or methyl group into the dye molecule. On the basis of these results the effects of the substituents are discussed.