Impact of Additive Hydrophilicity on Mixed Dye-Nonionic Surfactant Micelles: Micelle Morphology and Dye Localization

The nonionic surfactant pentaethylene glycol-monododecylether C12E5 forms micelles in aqueous solutions with a lower critical solution temperature. This characteristic solution behavior of C12E5 is independent of the pH. Such micelles are used to solubilize a large variety of active guest molecules like for instance dyestuffs. An example is an acidic azo dye termed Blue used as a hair colorant. Depending on the pH, Blue gradually changes its hydrophilicity from the protonated BlueH at pH = 2 to the bivalent anion Blue2- at pH = 13 while keeping the shape and size of Blue essentially unchanged. These features of C12E5 and Blue offer the unique chance to investigate the sole impact of a tunable hydrophilicity of a guest molecule on the solution behavior of mixed micelles of the guest and C12E5. Accordingly, the present work establishes a phase diagram of Blue-C12E5 micelles and analyzes their morphology including the spatial distribution of Blue in the micelles as a function of the hydrophilicity of Blue. Small angle neutron scattering reveals the size and shape of the micelles, and detailed contrast matching of the C12E5 supported by 1H NMR with NOESY provided insight into the localization of Blue within the micelles as its hydrophilicity changes.

SANS contrast matching for the unambiguous localization of anionic dye in cationic surfactant micelles

Contrast variation in small-angle neutron scattering (SANS) was successfully applied to localize the anionic azo dye Blue in co-assemblies with the cationic surfactant dodecyltrimethylammoniumbromide (DTAB). For this purpose, the scattering contrast between DTAB and the aqueous solvent was eliminated by SANS contrast matching, leaving only the scattering signal from Blue to be detected. Results obtained by contrast matching were confirmed by NOESY NMR-spectroscopy, showing that Blue interacts with the positively charged DTAB head groups and with up to the 4th neighbouring methylene group of the DTAB C12-alkyl chain. Its localization in the outer layer of the Blue-DTAB co-assembly explains the uniaxial growth of spheroidal DTAB micelles to wormlike micelles with increasing [Blue] : [DTAB] ratio from 0 : 1 to 1 : 3. This is in line with the concept of the packing parameter for amphiphilic substances.

The Effect of Electrolytes on the Interaction of C. I. Reactive Orange 16-Tetradecyltrimethylammonium Bromide

The aim of this study is to investigate the interaction of a cationic surfactant tetradecyltrimethyl ammonium bromide (TTAB) on the electronic absorption spectra of azo dye Reactive Orange 16 (RO16) and to observe the effects of the kind and concentration of electrolytes on these interactions by means of UV-Vis spectroscopy in submicellar and micellar concentration range at a certain temperature (303 K). TTAB affects the electronic absorption spectra of dye solution that is dye-surfactant interaction results into formation of complex and therefore, a decrease in maximum absorption spectra (1.577 at 494 nm). The electrolyte anions cause an increase on the absorbance of TTAB–RO16 ion-pair complex in the following order: Br– > Cl– > SO42– > NO3– > CN– and also for cations; Na+ > K+ > NH4+ > Mg2+. The increase or decrease on absorption spectra of RO16-TTAB solution depends on concentration range of the electrolyte added.

Reduction of Methylene Blue by Ascorbic Acid: Kinetic and Thermodynamic Aspects

This article reports the reduction of methylene blue (MB) by ascorbic acid (H2As) in basic aqueous and micellar solutions. Ascorbate ion (As2–) is found to be an effective reducing agent for the decolorization of methylene blue under ambient condition. Effects of salting-in and salting-out agents have been investigated for real-time application in the reduction process. The salting-in agent urea has been found to uniquely enhance the rate of the reduction of MB by As2– in the presence of micelles. Detailed kinetic and thermodynamic aspects have been considered to realize the interaction between methylene blue and ascorbate ion. Kinetic studies revealed that the reaction follows pseudo first order reaction kinetics.

Effects of Electrolytes on Interfacial and Micelle Properties of C.I. Reactive Orange 16 – Dodecylpyridinium Chloride Binary System

The effect of electrolytes on the interaction between the anionic dye C.I. Reactive Orange 16 and the cationic surfactant dodecylpyridinium chloride was investigated using surface tension measurement in a certain concentration range. The influence of the concentration of electrolyte on critical micelle concentration (CMC) values was observed in the following order; 0.1 M NaCl > 0.5 M NaCl > 1.0 M NaCl. Also, the influence of the electrolyte cations was observed as Na+ > Mg2+ > K+. An increase on CMC values of dye-surfactant solution with increasing electrolyte concentration is explained as charge screening and also the decrease in these values for higher concentration of electrolyte is attributed to the change of micelle shape. Furthermore this change is due to ionic polarizability, valency and hydrated radius. Using Rubingh's regular solution theory, the values of micellar interaction parameters (β), were found as negative in all studied mixtures.

Spectroscopic studies of interactions between C.I. Reactive Orange 16 with alkyltrimethylammonium bromide surfactants

In the present study, the influence of surfactants on spectral properties of an azo dye in aqueous solutions has been investigated by means of UV-vis spectroscopy in submicellar and micellar concentration range. The spectral signature of the polarity of the azo dye C.I. Reactive Orange 16 (RO16) exhibits sensitivity to the polarity of the dye's environment. This dependence of absorption on microenvironment was used to investigate the ion pair complex formed from electrostatic interaction of a series of alkyltrimethylammonium bromide surfactants (CmTAB, m=12, 14, 16 and 18) with the anionic azo dye RO16. It was observed that the aggregation of surfactant and dye takes place at surfactant concentration far below the critical micelle concentration of the individual surfactant. Aggregation is reflected by the appearance of a new absorption band in the spectrum of the dye. Spectral behavior of dye-surfactant solution with varying concentration of surfactant confirms that electrostatic interaction between dye and surfactant occurs up to a certain level. Beyond this concentration, with addition of surfactant, micelles occur and all dye molecules are accommodated into a normal micelle as monomeric molecules. The short-range hydro phobic interactions are very important factors as the long-range electrostatic forces on the dye-surfactant aggregation in aqueous solution. The effect of the length of the alkyl chain of the surfactant on the complex formation between cationic surfactant and reactive dye was that the hydrophobicity of alkyl chains plays an important role in complex formation. Going from less hydrophobic solution to the more hydrophobic micellar environment, the occurrence of complex is found at lower surfactant concentration. Because the CMC values of dye-surfactant solution are decreased with increasing alkyl chain length.

C.I. Reactive Orange 16-dodecylpyridinium chloride interactions in electrolytic solutions

The effect of electrolytes on the interaction between an anionic dye and a cationic surfactant was investigated spectrophotometrically in submicellar concentration range at certain temperature. The spectral change of the azo dye C.I. Reactive Orange 16 (RO16) exhibits a high sensitivity to the polarity of dye's environment. Dodecylpyridinium chloride (DPC) affects the electronic absorption spectra of dye solution that is dye-surfactant interaction results formation of complex and therefore a decrease in maximum absorption spectra (1.577 at 494 nm). The electrolyte cations cause an increase of the absorbance of DPC-RO16 ion-pair complex in the following order: Ca(2+)>Na(+)>NH(4)(+)>K(+)>Mg(2+), also for electrolyte anions Br(-)>Cl(-)>SO(4)(2-). Furthermore, this order can be changeable with increasing electrolyte concentration. The increase on absorbance value with increasing electrolyte concentration is explained as charge screening. The increase or decrease on absorption spectra of RO16-DPC solution depends on concentration range of the electrolyte added. As an increase on absorbance value with increasing electrolyte concentration is explained as charge screening, a decrease in this value for higher concentration of electrolyte is attributed as the charge of micelle shape.

Tetraiodophenolsulfonphthalein as a spectral substitute to characterize the complexation between cationic and anionic surfactant

The complexation of cetyltrimethylammonium bromide (CTAB) with sodium dodecyl sulfate (SDS) with sodium dodecyl benzene sulfonate (SDBS), with tetraiodophenolsulfonphthalein (TIPST) as a spectral substitute was investigated at pH 5.89 and 8.30 by the microsurface adsorption--spectral correction (MSASC) technique. The aggregations of TIPST, SDS, and SDBS on CTAB obeyed the Langmuir isothermal adsorption. The aggregates TIPST-CTAB, TIPST2-CTAB3, SDS3-CTAB2, and SDBS3-CTAB2 were formed at 20 degrees C and the binding constants of all the aggregates were determined. The replacement of TIPST-binding CTAB monomer with SDS or SDBS at pH 5.89 was applied to the quantitative determination of anionic detergent (AD) in water with satisfactory recovery.

Interaction of Epirubicin HCl with Surfactants: Effect of NaCl and Glucose

The interaction of an antitumoural drug, Epirubicin HCl, with anionic (sodiumdodecylsulfate; SDS), cationic (cetyltrimethylammonium bromide; CTAB), and nonionic (t-octylphenoxypolyethoxyethanol; TX-100, polyoxyethylenesorbitanmonolaurate; Tween 20) surfactants has been studied by absorption spectra as a function of surfactant concentration ranging from the premicellar to postmicellar region. At the concentrations below the critical micelle concentration (CMC), the equilibrium complex formation constant between Epirubicin cations and SDS anions has been determined by Job's method. Above the CMC, binding constant (K(b)) of Epirubicin to various types of micelles has been calculated by means of the Benesi-Hildebrand Equation. The nonionic surfactant micelles showed stronger interaction than the ionic SDS micelles, and the binding tendency of Epirubicin followed the order: Tween 20 > TX-100 > SDS. Binding of Epirubicin also has been studied in the presence of NaCl and glucose because it is administered to patients intravenously in 0.9% NaCl or 5% glucose solution. The additives have been observed to affect the CMC of the surfactants and the Epirubicin-micelle binding constant appreciably. The presence of NaCl and glucose lowered the CMC of all the surfactants studied. The binding constant of Epirubicin decreased in the presence of NaCl but increased in the presence of glucose. The equilibrium complex formation constant between Epirubicin and SDS decreased in the presence of NaCl compared with purely aqueous media.

Interaction of surfactants and aminoindophenol dye

The interaction of dye and surfactants was studied by their spectroscopic and surface properties. Large bathochromic shift (15 nm) in the absorption spectrum was found for aminoindophenol dye at high pH in cationic surfactant, while there is no significant shift in anionic, zwitterionic and nonionic surfactant solutions. The static and dynamic surface properties show there is strong interaction in mixture of cationic surfactant and aminoindophenol dye. Interaction of dye and surfactants on surface and in solution is correlated to the intensity of dye deposition on fiber. The charge complex formation between cationic surfactant and aminoindophenolic dye delays the dye diffusion into keratin fiber. The stronger is the dye/surfactant interaction, the lower dye deposition and diffusion become.