Drying dissipative structures of nonionic surfactants in aqueous solution

Macroscopic and microscopic dissipative structural patterns form in the course of drying a series of aqueous solutions of polyoxyethylenealkyl ethers. The shift from the single round hill with accumulated surfactant molecules to the broad ring patterns of the hill in a macroscopic scale occurs as the HLB (hydrophile-liophile balance) of the surfactant molecules increases. The patterns correlate intimately with the HLB values of the surfactants. Microscopic patterns of small blocks, starlike patterns, and branched strings are formed. The size and shape of the surfactant molecules themselves influence the drying patterns in part. The pattern area and the time to dryness have been discussed as a function of surfactant concentration and HLB of the surfactants. The convection flow of water accompanying the surfactant molecules, the change in the contact angles at the drying frontier between solution and substrate in the course of dryness, and interactions among the surfactants and substrate are important for the macroscopic pattern formation. Microscopic patterns are determined in part by the shape and size of the molecules, translational Brownian movement of the surfactant molecules, and the electrostatic and hydrophobic interactions between surfactants and/or between the surfactant and substrate in the course of solidification.     

Interaction behaviour in ultrafiltration of nonionic surfactants Part II. Static adsorption below CMC

Two homologous series of nonionic surfactants, namely Rhom and Haas' tritons (alkylphenol ethoxylates) and Shell dobanols (dobanol ethoxylates) were used to characterize surface properties of ultrafiltration membranes. Static adsorption experiments were carried out to reveal the interactions developed between the membrane and the nonionic surfactant. The surfactant adsorption on the membranes depends on the chemical composition and structure of both the membranes and the surfactants used, as both chemical composition and structure determine the type of interactions controlling this adsorption illustrated on the adsorption isotherms. Distinct different behaviour was exhibited by four types of membranes of the same nominal molecular weight cut-off. The influence of pH and ionic strength was studied also.     

Self-assembly of mixed anionic and nonionic surfactants in aqueous solution

We present the phase diagram and the microstructure of the binary surfactant mixture of AOT and C(12)E(4) in D(2)O as characterized by surface tension and small angle neutron scattering. The micellar region is considerably extended in composition and concentration compared to that observed for the pure surfactant systems, and two types of aggregates are formed. Spherical micelles are present for AOT-rich composition, whereas cylindrical micelles with a mean length between 80 and 300 ? are present in the nonionic-rich region. The size of the micelles depends on both concentration and molar ratio of the surfactant mixtures. At higher concentration, a swollen lamellar phase is formed, where electrostatic repulsions dominate over the Helfrich interaction in the mixed bilayers. At intermediate concentrations, a mixed micellar/lamellar phase exists.     

Removal of heavy metals from wastewater using micellar enhanced ultrafiltration technique: a review

Application of Micellar enhanced ultrafiltration (MEUF) for the removal of different heavy metals has been reviewed. It is considered an economical alternative available to the conventional membrane separation process, because it reduces the requirement of higher pressure and high membrane costs. MEUF is a separation processes which uses surfactants and ultrafiltration membranes to remove multivalent ions from wastewater with high percent rejection using electrostatic attraction between metals and micelles.     

Organolead chemistry : Part VI. Removal of methyllead compounds from aqueous solution by reaction with zinc

Trimethyllead chloride or dimethyllead dichloride in aqueous solution reacts with zinc to give ultimately methane, lead and zinc oxide and zinc chloride. The reactions proceed in two distinct stages, the first involving rapid removal of the organolead species from solution and the second leading to the final products. The intermediacy of organometallic compounds with lead-zinc bonds, which undergo 1,2-shift of methyl groups from lead to zinc followed by hydrolysis of the resulting methylzinc species, is suggested. The reactions have application in the treatment of effluents from the manufacture of tetramethyllead.     

A concentration polarization model for the ultrafiltration of nonionic surfactants

A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration. The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data.     

Application of micellar enhanced ultrafiltration for the removal of sunset yellow dye from aqueous media

In this article, we report the removal of a reactive dye, viz. sunset yellow, from the aqueous solution using micellar media of two cationic surfactants, viz. cetyltrimethylammonium bromide and ethyl hexadecyldimethyl ammonium bromide (. The values of rejection coefficient (R%) and permeate flux (J) have been calculated using membranes with different pore sizes, viz. 10,000 (10k) molecular weight cutoff (MWCO) and 30,000 (30k) MWCO at 1.5 bar transmembrane pressure. The membrane of 30k MWCO was found to be more suitable in order to retain the dye molecules incorporated in the micelles.     

Quantifying the hydrophobic effect. 2. A computer simulation-molecular-thermodynamic model for the micellization of nonionic surfactants in aqueous solution

In this article, the validity and accuracy of the CS-MT model is evaluated by using it to model the micellization behavior of seven nonionic surfactants in aqueous solution. Detailed information about the changes in hydration that occur upon the self-assembly of the surfactants into micelles was obtained through molecular dynamics simulation and subsequently used to compute the hydrophobic driving force for micelle formation. This information has also been used to test, for the first time, approximations made in traditional molecular-thermodynamic modeling. In the CS-MT model, two separate free-energy contributions to the hydrophobic driving force are computed. The first contribution, gdehydr, is the free-energy change associated with the dehydration of each surfactant group upon micelle formation. The second contribution, ghydr, is the change in the hydration free energy of each surfactant group upon micelle formation. To enable the straightforward estimation of gdehydr and ghydr in the case of nonionic surfactants, a number of simplifying approximations were made. Although the CS-MT model can be used to predict a variety of micellar solution properties including the micelle shape, size, and composition, the critical micelle concentration (CMC) was selected for prediction and comparison with experimental CMC data because it depends exponentially on the free energy of micelle formation, and as such, it provides a stringent quantitative test with which to evaluate the predictive accuracy of the CS-MT model. Reasonable agreement between the CMCs predicted by the CS-MT model and the experimental CMCs was obtained for octyl glucoside (OG), dodecyl maltoside (DM), octyl sulfinyl ethanol (OSE), decyl methyl sulfoxide (C10SO), decyl dimethyl phosphine oxide (C10PO), and decanoyl-n-methylglucamide (MEGA-10). For five of these surfactants, the CMCs predicted using the CS-MT model were closer to the experimental CMCs than the CMCs predicted using the traditional molecular-thermodynamic (MT) model. In addition, CMCs predicted for mixtures of C10PO and C10SO using the CS-MT model were significantly closer to the experimental CMCs than those predicted using the traditional MT model. For dodecyl octa(ethylene oxide) (C12E8), the CMC predicted by the CS-MT model was not in good agreement with the experimental CMC and with the CMC predicted by the traditional MT model, because the simplifying approximations made to estimate gdehydr and ghydr in this case were not sufficiently accurate. Consequently, we recommend that these simplifying approximations only be used for nonionic surfactants possessing relatively small, non-polymeric heads. For MEGA-10, which is the most structurally complex of the seven nonionic surfactants modeled, the CMC predicted by the CS-MT model (6.55 mM) was found to be in much closer agreement with the experimental CMC (5 mM) than the CMC predicted by the traditional MT model (43.3 mM). Our results suggest that, for complex, small-head nonionic surfactants where it is difficult to accurately quantify the hydrophobic driving force for micelle formation using the traditional MT modeling approach, the CS-MT model is capable of making reasonable predictions of aqueous micellization behavior.     

Dimeric and oligomeric surfactants. Behavior at interfaces and in aqueous solution: a review

Dimeric and oligomeric surfactants are novel surfactants that are presently attracting considerable interest in the academic and industrial communities working on surfactants. This paper first presents a number of chemical structures that have been reported for ionic, amphoteric and nonionic dimeric and oligomeric surfactants. The following aspects of these surfactants are then successively reviewed the state of dimeric and oligomeric surfactants in aqueous solutions at concentration below the critical micellization concentration (cmc); their behavior at the air/solution and solid/solution interfaces; their solubility in water, cmc and thermodynamics of micellization; the properties of the aqueous micelles of dimeric and oligomeric surfactants (ionization degree, size, shape, micropolarity and microviscosity, solution microstructure, solution rheology, micelle dynamics, micellar solubilization, interaction between dimeric surfactants and water-soluble polymers); the mixed micellization of dimeric surfactants with various conventional surfactants; the phase behavior of dimeric surfactants and the applications of these novel surfactants.     

Spectroscopic properties of polycyclic aromatic compounds Part 6. The nitromethane selective quenching rule visited in aqueous micellar zwitterionic surfactant solvent media

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 58 representative PAH solutes dissolved in micellar N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and in micellar N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate solvent media. Results of measurements show that zwitterionic surfactants can be considered, for the most part, as providing a polar solubilizing media as far as the nitromethane selective quenching rule is concerned. Nonalternant PAHs that contain electron donating methoxy- and hydroxy-functional groups (and methyl-groups to a much lesser extent) are noted exceptions.     

The modification of the triple helical structure of gelatin in aqueous solution 3. The influence of nonionic surfactants

Using CD-measurements the influence of nonionic surfactants (dodecyl polyoxyethylene, ethoxylated para tert. octyl phenol, commercial nonionic WON 100 and octyl diethyl phosphinoxid) on the secondary structure of gelatin in aqueous solutions was investigated. At surfactant concentrations smaller than the c.m.c. the triple helical content of the gelatin is increased. At concentrations exceeding the c.m.c. the triple helical content decreases. Chain reversals of the peptide chains after the destruction of the triple helical structure were shown to appear in acidic environment at 298 K. This destruction is reversible by rechilling the solution.     

Tuning J-aggregates of tetra(p-hydroxyphenyl)porphyrin by the headgroups of ionic surfactants in acidic nonionic micellar solution

J-aggregates of the diacid form of tetra(p-hydroxyphenyl)porphyrin (THPP) were found to be stable in nonionic micellar solution in the presence of trace ionic surfactant with an oxyacid headgroup. The excitation energy of exciton coupling depends systematically on the headgroups of the ionic surfactant, by which strong and weak coupling can be accomplished in the J-aggregates. The J-aggregates have two strong exciton bands corresponding to the B- and Q-bands of the protonated monomers. The total fluorescence of THPP is quenched through aggregate formation. A strong and sharply peaked resonance light-scattering signal that suggests a delocalized excitonic state was observed just slightly to the red of the absorption maximum of the J-aggregates. The overall resonance Raman intensities appeared to be stronger in the aggregates than in the monomers. In the kinetics of aggregation induced by sodium dodecyl sulfate (SDS), no characteristics of autocatalyzed reactions were observed, and there was only a logarithmic phase that lasted only several seconds.     

Simple determination of nonionic surfactants in highly-polluted aqueous samples

This study examined the direct spectrometric method for determining non-ionic surfactants in highly-polluted samples (i.e., soil leachates) containing high concentrations of humic acids. Meso-tetra-(3,5-dibromo-4-hydrooxyphenyl)-porphyrin served as a coloration agent. The method was tested by use of two polyethoxylate/polypropoxylate — based non-ionic surfactants: Triton CF-21 containing aromatic groups in the structure and Novanik 1047A containing only linear hydrocarbon chains. The main goal was to quantify the influence of interfering species to the results. A test for coincidence of regression lines was employed for objective evaluation of the humic acid influence on the determination. It was observed that for linear surfactant Novanik 1047 A the method provides reliable result and thus, can serve for routine analyses. Regarding Triton CF-21, an interfering effect of humic acids was observed; however, after sufficient dilution of the samples, the method can be used as well. Finally, the method can be used for simple analyses of problematic samples without complicated sample-pretreatment.      

Chlorination of aromatic compounds in micellar media: regioselectivity

Chlorination of phenol and ortho-chlorophenol was studied in micellar media in order to observe the effect on regioselectivity. Hydrogen peroxide/hydrochloric acid-aqueous system, which is environmentally a safer route was employed for chlorination. Selectivity ratio was found to be dependent on the nature and concentration of the surfactant. Ortho/para selectivity ratio up to 12 was realized for the chlorination of phenol. 2,6-/2,4-dichlorophenol ratio up to 1.01 was realized for the chlorination of ortho-chlorophenol.     

Removal of tetramethyl ammonium hydroxide from synthetic liquid wastes of electronic industry through micellar enhanced ultrafiltration

In this paper, the separation of tetramethyl ammonium hydroxide (TMAH) from synthetic liquid wastes of electronic industry is carried out by using a micellar enhanced ultrafiltration (MEUF) process. This treatment represents the first step of an integrated process, aimed at the recovery of TMAH and surfactant and water reuse. The laboratory tests are carried out with an ultrafiltration module using initial solutions having a concentration of pollutant equal to 2?g/L and by adding sodium dodecyl sulfate as a surfactant, at a concentration in the range 4–10?mM/L, that is, under and above its critical micellar concentration (CMC). The experiments have been carried out at a fixed temperature of 25°C. The obtained results showed that very good percentage removals of TMAH are achieved (99%), especially when the surfactant was above the CMC.     

Viscoelastic micellar solutions in a mixed nonionic fluorinated surfactants system and the effect of oils

Formation and rheological behavior of viscoelastic wormlike micelles in aqueous solution of a mixed system of nonionic fluorinated surfactants, perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)nH (abbreviated as C8F17EOn) was studied. In the water-surfactant binary system C8F17EO20 forms an isotropic micellar solution over wide concentration range (>85 wt %) at 25 degrees C. With successive addition of C8F17EO1 to the aqueous C8F17EO20 solution, viscosity of the solution increases swiftly, and a viscoelastic solution is formed. The oscillatory rheological behavior of the viscoelastic solution can be described by Maxwell model at low-frequency region, which is typical of wormlike micelles. With further addition of C8F17EO1, the viscosity decreases after a maximum and phase separation occurs. Addition of a small amount of fluorinated oils to the wormlike micellar solution disrupts the network structure and decreases the viscosity sharply. It is found that polymeric oil, PFP (F-(C3F6O)nCF2CF2COOH), decreases the viscosity more effectively than the perfluorodecalin (PFD). The difference in the effect of oil on rheological properties is explained in terms of the solubilization site of the oils in the hydrophobic interior of the cylindrical aggregates, and their ability to induce rod-sphere transition.     

Emission behavior of 1-methylaminopyrene in aqueous solution of anionic surfactants

A new fluorescent probe, methylamino derivative of pyrene, has been considered to characterize the concentration dependent emission behavior of an aqueous solution of anionic surfactants, viz., SDS, DSS, and SDBS. It was found that the emission of the probe is uniquely sensitive to the changes in surfactant (anionic) concentration due to the functional group effect of the probe over the parent moiety, pyrene. Here, 1-methylaminopyrene (MAP) showed significant quenching of emission well below the critical micellar concentration (cmc) of the surfactant. Excimer emission of the probe due to the formation of premicellar aggregates of the surfactant solutions at a concentration close to but below the cmc and again an enhanced emission of the probe above the cmc were observed as a consequence of definite MAP-surfactant interactions. These observations assisted the possible quantification ofsurfactant concentrations and their chain length dependent premicellar aggregate formations. Significant monomer emission in relation to probe distribution in micelle was analytically authenticated. Dynamic light scattering (DLS) studies revealed the incorporation of the probe molecules in the micellar core. The fluorophore emission showed nonlinear behavior when the surfactant concentration was far above the cmc. Abrupt changes in the emission characteristics in relation to the micellar concentration led to the determination of the cmc of the surfactants.     

On the calculation of diffusion coefficients and aggregation numbers of nonionic surfactants in micellar solutions

The calculation of the diffusion coefficients of nonionic surfactants as functions of their concentrations in micellar solutions has been analyzed within the framework of the quasi-chemical version of the law of mass action. The methods of the introduction of initial calculation parameters, calculation scheme for an ideal mixture of monomeric molecules and micelles, and corrections for varying solution viscosity have been considered. Numerical estimations have been performed using aqueous tetraoxyethylene octyl ether, pentaoxyethylene hexyl ether, and octyl-β-D-glucopyranoside solutions as examples.     

Resistance in series model for micellar enhanced ultrafiltration of eosin dye

A study has been performed to quantify the extent of flux decline during micellar enhanced ultrafiltration (MEUF) of an acid dye (eosin red) using hexadecyl (cetyl) pyridinium chloride as the cationic surfactant. Effects of the operating conditions, e.g., transmembrane pressure drop and feed-surfactant-to-dye ratio, on the permeate flux profile and observed retention have been investigated in an unstirred batch ultrafiltration (UF) cell. A simple resistance-in-series model has been used to quantify the flux decline. From the flux decline history, it has been found that the membrane permeability decreases rapidly due to reversible pore blocking and further flux decline is caused by the growth of a gel-type layer over the membrane surface. The different resistances and growth kinetics of the gel layer have been investigated as functions of the operating conditions.