Review of the literature shows that the study of interaction of dye-surfactants and dye-amino acids provide useful important information about physiological systems because of its widespread applications and relatively complex behaviour. These investigations are important from point of view of technology of dyeing processes as well as for chemical researches, such as biochemistry, analytical chemistry, and photosensitization. Most of the work on amino acids and biomolecules have been carried out in pure and mixed aqueous solutions but the investigation of spectroscopic, tensiometric and thermodynamic properties of amino acids in aqueous dye solution has rarely been done. On the other hand although studies have been made involving dye–surfactant interactions, yet this particular field of research is still important for improvised dyeing process in terms of theoretical, technological, environmental as well as economic point of view [1]. The dye-surfactant interaction has importance in many areas such as the spectral behaviour of dye in microheterogenous systems, dye-sensitized solar cells, and photocatalysis like photocatalytic water splitting. It is important to understand how surfactants and dyes interact in aqueous solutions to clarify the mechanisms of dyeing and other finishing procedures. Hence the investigation of interaction between surfactants / amino acid in aqueous dye solution was undertaken using different useful techniques.
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Mata et. al [2] investigated the physicochemical properties of pure cationic surfactants (quaternary salts) in aqueous solution by means of surface tension (at 303.15 K), conductance (at 293.15–333.15 K), dye solubilization and viscosity measurements. From the results it appeared that changes in the nature of the surfactant (such as changes in chain length, polar head group or counter ion) have a severe effect on the subsequent self-assembly in water. The increase in hydrophobic character of the surfactant decreases the CMC, induces sphere-to-rod transition at lower concentration and increases the solubilizing power of surfactant towards orange OT. Viscosity results indicated that the size of the micelles is relatively small at CMC and grows longer with increasing surfactant concentration. The plots of differential conductivity, (dk/dc)T,P, versus the total surfactant concentration enables us to determine the CMC values more precisely.
The critical micelle concentration (cmc) and degree of ionization (β) of cationic surfactants, dodecyldimethylethylammonium bromide (DDAB) and dodecyltrimethylammonium chloride (DTAC) in aqueous media were determined by Mehta et. al [3] from the conductivity measurements at different temperatures. The cmc behavior of DDAB and DTAC was analyzed in comparison with the results of DTAB in terms of effect of counter ion and increase in alkyl chain. It was observed that by changing the counter ion from chloride (DTAC) to bromide along with the increase in alkyl chain on polar head group (DDAB), the cmc shows a decrease. Thermodynamics of the system reveals that at lower temperatures, the micellization in case of DDAB was found to be entropy-driven, while at higher temperatures it was enthalpy driven. In DTAC system only entropic effect dominates over the entire temperature range.
The aggregation properties of a cationic surfactant, DTAB, at different compositions in water-DMSO mixtures was studied by Véronique Peyre et. al [4] using combination of techniques such as SANS, conductivity, and density measurements. Different complementary approaches were used for the interpretations of data. This multi-technique study explains the reason for the decrease in ionization degree, role of solvation in micellization and emphasizing the dissymmetric solvation of the chain by DMSO and the head by water. The study is interesting from the point of view that micellization process has been described by using combined analysis from molecular to macroscopic scale.
Apparent and partial molar volumes of decyldimethylbenzylammonium chloride (C10DBACl) at (15, 25, and 35) °C have been calculated from results of density measurements by A. G. Perez et. al [4]. The specific conductivities of the solutions have been determined at the same temperatures. The results served for the estimation of critical micelle concentration, cmc, ionization degree, (β), and standard free energy of micellization, (∆G
), of the surfactant.
J. J. Galan, J. R. Rodrıguez [5] studied the molality dependence of specific conductivity of pentadecyl bromide, cetylpyridinium bromide and cetylpiridinium chloride in aqueous solutions in the temperature range of 30–45 â-‹C. The critical micelle concentration (cmc) and ionization degree of the micelles, β, were determined directly from the experimental data. Comparing our results for C16PBr and C16PCl water solutions, it can be observed that the substitution of the bromide anion by the more hydrophilic chloride leads to an increase in cmc by a factor of approximately 1.3.
Chanchal Das and Bijan Das [6] have studied the micellization behavior of three cationic surfactants, viz., hexadecyl-, tetradecyl-, and dodecyltrimethylammonium bromide (CTAB, TTAB, and DTAB, respectively) in ethylene glycol (EG) (1) + water (2) mixed solvent media with varying mass fractions of EG (w1) by means of electrical conductivity and surface tension measurements. Temperature dependence of the critical micelle concentrations was also investigated to understand the micellar thermodynamics of these systems. From the study of the temperature dependence of the cmc of these surfactants in the EG (1) + water (2) mixture with w1 ) 0.30, they had demonstrated that the micellization was mainly governed by an enthalpy-entropy compensation effect. Data on the thermodynamics of adsorption demonstrate that the surface activity of these surfactant decreases with the addition of EG to water at a given temperature and that the adsorption of surfactant at the air/mixture interface takes place spontaneously.
The micellisation behaviour of cetyltrimethylammonium bromide (CTABr) in different mass fraction (17–47) of ethylene glycol (EG), dimethylsulfoxide (DMSO), and dimethylformamide (DMF)–water mixed solvents, was studied by Olaseni et. al [7] using electrical conductivity measurement at different temperatures (293.1–313.1 K). The results of the thermodynamic analysis showed that addition of organic solvents, which are principally located in the bulk phase made the micellisation process less spontaneous. The London-dispersion interaction represented the major attraction force for micellisation and micellisation proceeded via an exothermic process.
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Sar Santosh K and Rathod Nutan [8] evaluated cmc, α value and the thermodynamic parameters of the process of micellization for alkyl (C12, C14, and C16) trimethylammonium bromide systems in presence of water-dimethylformamide (5-20 % v/v) binary mixtures over a temperature range of 298-318 K. It was observed that both the cmc and α value were dependent upon the (v/v %) of solvent and temperature and the micellization tendency of cationic surfactant decreases in the presence of solvents. It was also observed that the micellization is favored in general by entropy and enthalpy at higher temperatures, whereas it is favored mainly by entropy at low temperatures.
A. Ali et. al [9] have studied the thermodynamic properties of sodium dodecyl sulphate in micellar solution of L-serine and L-threonine by fluorescence spectroscopy and dynamic light scattering techniques. They observed a decrease in cmc of SDS in Thr solutions as compared to that in Ser. The determined values of ∆G become increasingly negative in the order: water > Ser >Thr, suggesting that the formation of micelles is more favorable in presence of amino acids than in pure water. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. On the basis of dynamic light scattering it was suggested that the size of SDS micelles was influenced by the presence of amino acids.
F. Jalali and A. Gerandaneh [10] computed the critical micelle concentration (cmc) of cetyltrimethylammonium bromide (CTAB) conductometrically in binary mixtures of water + cosolvent at various temperatures and in the presence of potassium bromide (2.0 – 14 X10-3 M). Dioxane and acetonitrile were used as cosolvents added to water. Addition of organic solvents to water increased the cmc value of CTAB, but the presence of KBr lowered cmc. Thermodynamic parameters of micellization, were evaluated for each solution according to the pseudo-phase model, and the changes observed in these parameters were related to the presence of KBr and cosolvents in aqueous solution.
The conductivity of (cosolvent C water) in the presence of increasing concentration of 1-hexadecylpyridinium bromide was measured at various temperatures by F. Jalali et al. [11]. Acetonitrile, dimethylformamide, dimethylsulfoxide, dioxane and ethylene glycol were used as cosolvents. From the conductivity data, the critical micelle concentration c.m.c., and the effective degree of counter ion dissociation α, were obtained at various temperatures. In all the cases studied, a linear relationship between ([c.m.c] / mol . dm-3) and the mass fraction of cosolvent in solvent mixtures was observed. The thermodynamic properties ∆Hand ∆Swere evaluated from the temperature dependence of the equilibrium constants for micellization of the surfactant. While the micellization process in pure water is both enthalpy and entropy stabilized, it becomes entropy destabilized in all solvent mixtures used; the values of ∆S being more negative with increase in the cosolvent content of the solvent mixtures. The resulting ∆H against T∆S plot showed a fairly good linear correlation, indicating the existence of an enthalpy–entropy compensation in the micellization process.
The effect of the simultaneous presence of an electrolyte (NaBr) and nonelectrolyte species (DMSO and AN) in aqueous solution on the micellization of HDPB was studied by F. Jalali and A. Shaeghi Rad [12]. They concluded that the presence of NaBr favors the micellization of HDPB mainly due to a decrease in repulsions between micelle head groups. Adding a cosolvent, such as DMSO or AN, to water inhibits the formation of micelles because of the increase in hydrophobic character of the mixed solvent, which increases the attraction of surfactant monomers toward the solvent.
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