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

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.     

Surface tension study of the interaction between two nonionic surfactants and two direct dyes

The complex-forming interaction between two direct dyes, CI Yellow 106 and CI Blue 78, and two nonionic surfactants, namely, polyoxyethylene nonyl phenyl ether (NP-12) and polyoxyethylene stearylamine (R-11), in aqueous solutions was studied. The estimation was made by measuring surface tension and critical micelle concentration (CMC) changes as a function of dye concentration. A decrease of NP-12 surface tension at low concentration and an increase of R-11 surface tension in the presence of both dyes were observed along with a significant decrease of NP-12 CMC values. A difference in the spectrophotometric absorbance of dye solutions in the presence of both surfactants, indicating a change in the environment of the dye chromophore, was also visible. These results confirm the formation of hydrophobic complexes of NP-12 and hydrophilic complexes of R-11 with both dyes.     

Solubilisation of dyes by surfactant micelles. Part 1; Molecular interactions of azo dyes with nonionic and anionic surfactants

An ultraviolet-visible spectroscopic investigation has been made of the interactions of a specially synthesised series of substituted, model arylazonaphthol dyes with nonionic and anionic surfactants. Changes in spectral features were recorded above the critical micelle concentrations, suggesting specific interactions of dyes with micelles of the respective surfactants. The affinity of the dye for the surfactant micelles increased when various p -substituent were incorporated in to the dyes. Similarly, there was a shift in azo–hydrazone tautomeric equilibria and an increase in measured dye p K _a values. Models are proposed for the location of dyes in nonionic or anionic micelles. Unlike earlier studies, it is concluded that the solubilised dye experiences only one environment in nonionic micelles but the specific location, i.e. whether preferentially incorporated in the hydrophobic micellar interior or in the more hydrophilic, outer polyoxyethylene layer, depends upon the nature of the substituent.     

Structural and Physicochemical Properties of a Polymerizable Surfactant Synthesized from <Emphasis Type="Italic">N</Emphasis>-Methylol Acrylamide

A new polymerizable nonionic surfactant with reactive vinyl groups has been synthesized from N‐methylol acrylamide using a two‐step procedure. The structure of the surfactant molecule was characterized by Fourier transform infrared, ¹H nuclear magnetic resonance and mass spectroscopy. The surface active properties alongside its self‐assembly properties were investigated by surface tension, electrical conductivity, and fluorescence spectroscopy measurements. As compared with other nonionic surfactants, this study showed that this polymerizable surfactant possesses slightly a higher critical micelle concentration (CMC) value and the surface tension value at CMC. The obtained CMC values were compatible among measurements, ca. 0.02–0.038 M. The evidence of micelle formation also provided by the zeta potential measurements and the obtained zeta potential values showed that the polymerizable surfactant solutions had limited stability. The hydrolysis stability and solubility of the polymerizable surfactant were also investigated. The solubility results have shown that it was soluble in polar solvents while insoluble in nonpolar solvents both at room temperature and 40 °C. The acidic and basic hydrolysis of the surfactant increased as the temperature increased and the hydrolysis stability was 180 min (basic medium) and 55 min (acidic medium) at 80 °C.     

Solubilisation of dyes by surfactant micelles. Part 2; Molecular interactions of azo dyes with cationic and zwitterionic surfactants

A UV–vis spectroscopic investigation has been made of the interactions of a specially synthesised series of o - and p -substituted, model arylazonaphthol dyes with the cationic and zwitterionic surfactants above and below their critical micelle concentrations at pH 10. Spectra of dyes incorporated in micelles of zwitterionic surfactant or cationic surfactant at pHs < 8 are similar to those found in nonionic micelles, i.e. dye substituents control its location similarly for all the micelle types. However, the common anion is selectively favoured in cationic micelle solutions at pH 10, due to electrostatic interactions within the micellar surface. Introduction of polar groups at either end of the molecule confines the dyes to the surface of either zwitterionic or cationic micelles and are characterised by atypical p K _A shifts. Electrostatic complexes between dyes and cationic or zwitterionic surfactants were formed in sub-micellar regions, those with cationic surfactant being sparingly soluble.     

Solubilisation study of water‐insoluble dye in cationic single/dimeric surfactant micelles: effect of headgroup,non‐polar tail,and spacer chain in aqueous and salt solution

The solubilisation of hydrophobic azo dye Orange OT in aqueous/salt solution in several cationic surfactant micelles was studied using UV‐vis spectroscopy. An attempt was made to correlate dye solubilising strength with adsorption/micellar characteristics. In our experiments we determined the change in solubilisation of hydrophobic dye when added to an aqueous solution of oppositely charged quaternary‐salt‐based cationic surfactants (conventional and gemini) and remarked on the probable location of the solubilised dye in the surfactant micelle. Results highlight the onset of dye solubilisation around the critical micelle concentration of each surfactant, which is influenced by the non‐polar tail, spacer, and polar headgroup, while no dye could be solubilised at concentrations below the critical micelle concentration. Orange OT solubilised almost linearly with increase in surfactant concentration at and above the critical micelle concentration. The change in colour intensity of the dye (darker below the critical micelle concentration, lighter at and above the critical micelle concentration) could be attributed to dye–surfactant interactions. Further dye solubilisation was observed in the presence of salt.     

Effect of tartrazine dye on micellisation of cationic surfactants: conductometric,spectrophotometric, and tensiometric studies

The interactions between anionic dye (tartrazine) and cationic surfactants (dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide) have been studied by conductometric, spectrophotometric, and tensiometric techniques. The conductance and surface tension of dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide in pure water as well as in aqueous tartrazine when plotted with surfactant concentration gave values of the critical micelle concentration at different temperatures. As well as increasing the length of the carbon chain of surfactants, the presence of tartrazine reduces the critical micelle concentration. From specific conductivity data, the counterion dissociation constant, standard free energy, enthalpy, entropy of micellisation, surface excess concentration, surface tension at critical micelle concentration, minimum area per molecule, surface pressure at critical micelle concentration, and Gibbs energy of adsorption were evaluated. Spectroscopic studies reveal that the binding of dye to micelles brings a bathochromic shift in dye absorption spectra that indicates dye–surfactant interaction.     

A spectroscopic and modelling study of polymer/dye interactions†

A spectroscopic study has been made of the comparative effectiveness of nonionic, zwitterionic and cationic polymers in binding model dyes. Addition of polymer produces smaller changes in the UV–vis spectra than observed in micellar solutions. Upon binding to polymers, the measured pK_A values of the model dyes decrease. The results of modelling and spectroscopic studies of the interaction between the model arylazonaphthol dyes are discussed in this paper. Addition of anionic surfactants, e.g. SDS, below their critical micelle concentrations disrupts polymer/dye binding, resulting in relocation of model dye to new sites formed from polymer/surfactant interactions. These sites are more apolar and produce spectra similar to those in corresponding micelles but with higher dye pK_A values and binding affinities. For the previous paper in this series see page 140; for parts 1 and 2 see refs 1 and 2, respectively.     

Decolorisation of reactive dye wastewater and the effect of surfactants using laccase

Laccase (benzenediol, oxidoreducase; Enzyme Commission Number) is a multi‐copper oxidase from biomass. Laccase enzyme recycling on molecular oxygen as an electron acceptor can be applied for the decolorisation of synthetic dyes. The decolorisation of 49 commercial reactive dyes using laccase was investigated. The effects of diverse structure surfactants on decolorisation are discussed. The absorption spectra of reactive dyes after a laccase biodegradable reaction were analysed. Reactive dyes based on anthraquinone and azo structures could be decolorised using the enzyme and their chemical structures broken. Reactive dyes based on an anthraquinone structure were easier to decolorise than those based on an azo structure. Surfactants could affect the decolorisation of dyes with an enzyme. The effect of nonionic surfactant on the decolorisation of anthraquinone dyes was the reverse. The cationic surfactant could improve the decolorisation rate of diazo dye. The effect of the anionic surfactant on dye decolorisation was small. Most commercial reactive dyes could be decolorised and biodegraded using a laccase enzyme under mild conditions. Laccase enzyme biotechnology has potential applications in the decolorisation of reactive dye wastewater.     

Adsorption and fixation behaviour of CI Reactive Red 195 on cotton woven fabric in a nonionic surfactant Triton X‐100 reverse micelle

To achieve the goals of saving water and being salt‐free in the coloration of cotton fabric with reactive dye, nonionic reverse micelles were prepared and optimised with a surfactant, Triton X‐100, n‐octanol and isooctane by injecting a small amount of CI Reactive Red 195 aqueous solution. The adsorption, diffusion and fixation of this dye on cotton fabric in Triton X‐100 reverse micelle and bulk water were then investigated. The equilibrium and kinetic data of the dye adsorption process were evaluated. The colour strength and fixation rate of cotton fabrics dyed in the micelle and in bulk water were also examined and compared. The results indicated that the amount of dye adsorbed increased with the increasing temperature and the initial dye concentration. The dye adsorption process could be described using the Langmuir isotherm and pseudo‐second‐order kinetic equations. It was found that CI Reactive Red 195 showed a stronger adsorption property on cotton fabric in Triton X‐100 reverse micelle than in bulk water without the addition of sodium chloride. Using Triton X‐100 reverse micelle as the dyeing medium offered the reactive dye better diffusion performance within the cotton fibre as compared with bulk water. Moreover, higher fixation of the dyes absorbed on the cotton fibre was achieved when the optimum concentration of sodium carbonate was used as the alkali agent in Triton X‐100 reverse micelle.     

Effect of Inorganic Additives on a Conventional Anionic–Nonionic Mixed Surfactants System in Aqueous Solution

The interaction between an anionic surfactant (sodium dodecyl sulfate) and a nonionic surfactant [polyoxyethylene (9.5) octyl phenyl ether] in aqueous salt solution was investigated using the surface tension method. The critical micelle concentration values were determined for the individual surfactants and their corresponding mixtures. The interaction parameter between the surfactants in the mixed micelles, the activity and activity coefficients in the mixed micelles, and the thermodynamic parameters were calculated using various approaches, viz., Clint, Rubingh, and Maeda models. It was observed that the critical micelle concentration of the mixed surfactants system reveals little deviation from ideality.     

Aggregation and Phase Separation Phenomenon of Amitriptyline Hydrochloride Under the Influence of Pharmaceutical Excipients

The interaction between the amphiphilic drug amitriptyline hydrochloride (AMT) and the nonionic surfactants used in drug delivery has been investigated. Herein, we report the micellization behavior of AMT in presence of ethoxylated alkyl phenols in aqueous medium and the clouding phenomenon in the absence and presence of different nonionic surfactants in buffer solution. The values of critical micelle concentration (CMC) of AMT obtained using the conductivity method, decrease as nonionic surfactant concentration increases. With an increase in temperature, the CMC first increases and then decreases. At 303.15 K, the maximum CMC values were obtained with or without nonionic surfactant. The results obtained indicate attractive interactions (synergism) between the two mixing amphiphiles in solution. The experimentally obtained critical micelle concentration (CMC) values are always lower than ideal CMC values. Micellar mole fraction (X₁) values, calculated by different proposed models, show the contribution of nonionic surfactant concentration. At a fixed drug concentration (50 mmol kg^?1) and pH (=6.7) nonionic surfactants show continuous increase in cloud point (CP). Increase in drug concentration and pH, in the presence of fixed amounts of nonionic surfactant, increases and decreases the CP, respectively.     

Dye–surfactant interaction in aqueous solutions

The interaction of four ionic dyes, C.I. Mordant Black 11, C.I. Mordant Black 17, C.I. Direct Yellow 50 and C.I. Basic Blue 9, with cationic and anionic surfactants was studied by absorption spectroscopy. The dyes interact strongly with oppositely charged surfactant in the premicellar concentration range and the appropriate values of constant of dye–surfactant complex formation were estimated. In addition, the most important factor affecting the number of dye particles solubilized in the surfactant micelle was its molecular mass.     

Synthesis and chemical hydrolysis of surface-active esters

A series of four homologous pure nonionic surfactants, all monoesters of tetra(ethylene glycol), were synthesized. The ester surfactants varied in the degree of substitution on the α-carbon of the acyl chain, from no substitution to 2-methyl, to 2-ethyl, and on to 2,2-dimethyl. All surfactants were based on C₈-acids except the 2-methyl-substituted, which was based on a C₇-acid. The ester surfactants were characterized by critical micelle concentration (CMC) and cloud point. Base-catalyzed hydrolysis was investigated by using ¹H NMR and tensiometry. The surfactants showed a pronounced difference in hydrolytic reactivity; the nonsubstituted surfactant was 90 times more reactive than the disubstituted, and the reactivity of the methyl-substituted surfactant was 14 times more reactive than the ethyl-substituted. Hydrolysis studies above the CMC revealed that the ester bond of the aggregated surfactant is protected from attack by hydroxide ions; thus, only surfactants in monomeric form are being cleaved.     

Natural dye–surfactant interactions: thermodynamic and surface parameters

The interaction of two Indian natural dyes, namely madder (Rubia cordifolia) and mallow (Punica granatum), with cationic surfactant cetyl trimethyl ammonium bromide and anionic surfactant sodium lauryl sulphate, has been studied. Spectrophotometric data showed a strong interaction between the natural dyes and the surfactants. The critical micelle concentration of the surfactants, determined by measurement of specific conductance and surface tension, was found to decrease on the addition of natural dyes in an aqueous solution of surfactants. The thermodynamic and surface parameters for the interaction have been evaluated.     

Experimental Study of CMC Evaluation in Single and Mixed Surfactant Systems, Using the UV–Vis Spectroscopic Method

In this study, the critical micellar concentration (CMC) of anionic, cationic and nonionic surfactants was determined using the UV–Vis spectroscopic method. Sodium lauryl sulfate (SDS) as anionic, hexadecyl-trimethyl-ammonium bromide as cationic, tert-octylphenol ethoxylates TOPEON (with N = 9.5, 7.5 and 35) and lauryl alcohol ethoxylate (23EO) as nonionic surfactants have been used. Concentration of surfactants varies both from below and above the CMC value in the pyrene solution. In addition, the amount of the CMC was determined using the values from the data obtained from the graph of absorbance versus concentration of surfactants. A comparative study was conducted between the results of the present study and the literature which shows a good agreement, in particular for TOPEO9.5 and LAEO23. Furthermore, the CMC value of SDS (as an ionic surfactant) in the presence of nonionic surfactants was also examined. The result reveals that with addition of small amount of nonionic surfactant to the anionic SDS surfactant, a decline in the CMC value of the anionic–nonionic system relative to the CMC of pure anionic surfactant was observed. In addition and for the first time, the effect of UV irradiation on the size of the micelle formations was studied. It was found that UV irradiation causes the formation of smaller micelles which is of prime concern in membrane technology.     

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

Dye loss from unfixed dyed fabrics has been found to be insensitive to change in surfactant type or concentration. There was accompanying dye transfer to white fabric but this was reduced by Synperonic A7 in the case of fabrics dyed with CI Direct Green 26, due to solubilisation of the dye in nonionic micelles. The anionic surfactant, SDS, selectively displaced dye from fixed dyed fabrics, paralleling its behaviour with water soluble polymers. Similarly, dye loss was related to concentration of surfactant monomer, the effect increasing with SDS concentration up to its critical micelle concentration. Other anionic surfactants have been found to exhibit a similar trend, the effect increasing with their increasing surface activity. The commercial polymeric fixatives, Tinofix ECO and Indosol E50, were the most effective of those studied and the single-chain cationic surfactant, CTAB, was the least effective.     

Ein Beitrag zur Messung der kritischen Micellkonzentration in nichtwäßrigen Lösungsmitteln

A Contribution on the Measurement of Critical Micelle Concentration in Non-Aqueous Solvents According to the known concepts, many surfactants form micelles even in organic solvents. A simple method for the determination of critical micelle concentration is based on the fact that dyes, when held in surfactant micelles, exhibit colour changes which can be measured conveniently by photometry. The critical micelle concentration of lauryl alcoholpolyglycolether(7) in dioxane, benzene, 1,2,4-trichlorobenzene and in carbon tetrachloride is in the region of 200-250 mg/l. The observed values are independent of the nature of dye (iodine, fluorescein and eosine). Traces of water increase the value. In aqueous solutions of surfactants the method based on the measurement of surface tension and the method employing a dye yield comparable values of critical micelle concentration which are in the region of 50 mg/l.     

Influence of mixed-surfactant on reductive dechlorination of trichloroethylene by zero-valent iron

Mixed nonionic and cationic surfactants were used to enhance the reductive dechlorination rate of trichloroethylene (TCE) with zero valent iron (ZVI). Among tested combinations of four cationic and three nonionic surfactants, a mixed surfactant system of hexadecyl-trimethyl ammonium (CTAB) and Brij30 at a mixing ratio of 1: 1 with 0.5 critical micelle concentration (CMC) exhibited the highest reaction rate constant, 0.0269 h⁻¹; the dechlorination rate constant of TCE with ZVI in the absence of surfactant was 0.0206 h⁻¹. The effect of this mixed surfactant on the reductive dechlorination of TCE was investigated using ZVI in a column to simulate field conditions. Unlike batch tests, column tests of the mixed surfactant system exhibited higher and lower TCE removal as compared to a nonionic and a cationic surfactant system, respectively. Consequently, if surfactants are applied for surfactant-enhanced aquifer remediation (SEAR), the performance of a permeable reactive barrier (PRB) system using ZVI to remove the residual TCE in groundwater might be affected by surfactant types; thus, the application should be carefully considered.     

Foulant interaction and RO productivity in textile wastewater reclamation plant

Foulant interaction and productivity of reverse osmosis (RO) membrane during textile wastewater reclamation were studied. Synthetic textile wastewater composed of salt, surfactant and reactive dye was used in the experiment. RO productivity was assessed using cross-flow membrane filtration unit. The result revealed that surfactant was the major cause of membrane fouling. When the surfactant concentration maintains lower than the critical micelle concentration (CMC), RO productivity was influenced by the concentration of surfactant. Therefore, lowest productivity was observed when the surfactant concentration approached CMC. When the concentration level rose above CMC, the surfactant micelle was formed within the bulk solution and this subsequently yielded an increase in RO productivity. The formed micelle decreased the adsorption capacity of surfactant monomer. Moreover, the appearance of aggregation between surfactant and reactive dye lowered the fouling potential of the mixtures especially when compared to the wastewater containing only surfactant at a higher concentration than CMC.