Aqueous Solutions Of Anionic Surfactants Research Articles

Investigation on Washing Effects for Nano-Bubble/Surfactant Mixtures in an Alternating Flow

Laundry wastewater is known to contribute to water pollution, and the need to reduce the amount of detergents used is recognized. Extensive research has focused on the washing effects of micro-bubbles and nano-bubbles, and mechanical work has been found to account for 50% of the washing effect. In the present research, a water/nano-bubble mixture and several types of surfactants were investigated in an alternating flow system. The nano-bubble water achieved a washing rate of about 5% greater than that of ion exchanged water. In addition, nano-bubbles mixed with an aqueous solution of surfactant exhibited a washing rate that depended on the ionization of the surfactant: the mixture of nano-bubbles and anionic surfactant exhibited a washing rate that was 10% higher than that of aqueous anionic surfactant solution without nano-bubbles. As measured by the du Nouy method, the surface tension of nano-bubble water and anionic surfactant/nano-bubble mixtures were lower than that of water and aqueous anionic surfactant solution, respectively. These results provide evidence of an enhanced washing effect for nano-bubble mixtures.

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.

Novel Counter Anion Effects of Added [Co(NH3)6]X3 (X− = Cl−, Br−, I−, or ClO4−) on Surface Tension Reduction in Aqueous Solutions of Anionic Surfactants

Abstract Surface tension of anionic surfactant solutions, sodium dodecyl sulfate (SDS) or sodium dodecylbenzenesulfonate (SBS) decreases remarkably in the presence of [Co(NH3)6]X3 (2.50 mM) (X− = Cl−, Br−, I−, or ClO4−) at 298 K, depending on the kind of counter anion X−. The magnitude of reduction is in the order ClO4− ≥ I− > Br− > Cl− for SDS solutions and ClO4− > Cl− > Br− > I− for SBS solutions at 0.03 mM surfactant concentrations.

Premicellar and micelle formation behavior of aqueous anionic surfactants in the presence of triphenylmethane dyes: protonation of dye in ion pair micelles

AbstractThe premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye–surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air–water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMCIP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye–surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air–water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.

Ultrathin Nanofibrous Films Prepared from Cadmium Hydroxide Nanostrands and Anionic Surfactants

We developed a simple fabrication method of ultrathin nanofibrous films from the dispersion of cadmium hydroxide nanostrands and anionic surfactants. The nanostrands were prepared in a dilute aqueous solution of cadmium chloride by using 2-aminoethanol. They were highly positively charged and gave bundlelike fibers upon mixing an aqueous solution of anionic surfactant. The nanostrand/surfactant composite fibers were filtered on an inorganic membrane filter. The resultant nanofibrous film was very uniform in the area of a few centimeters square when the thickness was not less than 60 nm. The films obtained with sodium tetradecyl sulfate (STS) had a composition close to the electroneutral complex, [Cd37(OH)68(H2O)n] x 6(STS), as confirmed by energy dispersive X-ray analysis. They were water-repellent with a contact angle of 117 degrees, and the value slightly decreased with the alkyl chain length of anionic surfactants. Ultrathin nanofibrous films were stable enough to be used for ultrafiltration at pressure difference of 90 kPa. We could effectively separate Au nanoparticles of 40 nm at an extremely high filtration rate of 14000 L/(h m2 bar).

Thermodynamic Properties of Micellization of Sodium Dodecylbenzene Sulfonate in the Aqueous-Rich Region of 1-Pentanol and 1-Hexanol

Apparent molar volumes, Φv, and isentropic compressibilities, κs, of the aqueous solutions of anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), have been derived from experimental densities, ρ, and speed of sound, u, data measured below 0.40 mol·kg−1 at T = (298.15, 303.15, 308.15, and 313.15) K using an Anton Paar densimeter (DSA-5000). Conductance measurements were also made for aqueous solutions of SDBS to obtain critical micelle concentration at the above temperatures. Apparent molar volumes and isentropic compressibilities of 1-pentanol and 1-hexanol dissolved in aqueous micellar solutions of SDBS were determined as a function of molalities of surfactant (0.05 and 0.1) mol·kg−1 and alcohols at T = (298.15 and 308.15) K. The standard partial molar volumes, Φov, and transfer volume, Φov(tr), have been calculated for rationalizing various interactions in the studied solutions. Viscosity measurements were made for the above-mentioned alcohols in aqueous solutions of SDBS to obtain relative visc...

Surface tension reduction (STR) in aqueous solutions of anionic surfactants with cobalt(III) complexes

It has been observed that, at 25.0 ± 0.1 ° C , [Co(NH 3) 6](ClO 4) 3, [Co(en) 3](ClO 4) 3, [Co(bpy) 3](ClO 4) 3, and [Co(phen) 3](ClO 4) 3 in the regions of 1.25–5.00 mM aqueous solutions cause a significant surface tension reduction (STR) of water by the surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SBS), suggesting the formation of the 1:1 and 1:2 association complexes, {[complex] 3+(S −)} 2+ and {[complex] 3+(S −) 2} + where [complex] 3+ = [Co(NH 3) 6] 3+, [Co(en) 3] 3+, [Co(bpy) 3] 3+, or [Co(phen) 3] 3+, S − = DS − or BS −. The effect of [Co(en) 3] 3+ on STR in SDS–water system is the largest due to a strong hydrophilic interaction between amino protons of [Co(en) 3] 3+ and sulfate oxygen atoms of DS −. The effects of [Co(en) 3] 3+, [Co(bpy) 3] 3+, and [Co(phen) 3] 3+ on STR in SBS–water system are significant and almost same, meaning that the hydrophilic interaction between [Co(en) 3] 3+ and the sulfonate group is comparable to the hydrophobic interaction between [Co(bpy) 3] 3+ or [Co(phen) 3] 3+ and the phenyl group of BS −. The Co(III) complexes of 1.25–5.00 mM are precipitated as {[complex] 3+(S −) 3} at 0.0295–0.173 mM of S −. The precipitates, {[Co(bpy) 3] 3+(S −) 3} and {[Co(phen) 3] 3+(S −) 3} can be dissolved at higher molar ratio of [S −]/[complex 3+] than 3.5 for SDS and 4.0 for SBS. This observation suggests that the aggregated premicelle [Co(bpy or phen) 3] 2(DS) − 7 or aggregated premicelle [Co(bpy or phen) 3](BS) − 4 is formed.

Soil flushing by surfactant solution: Pilot-scale demonstration of complete technology

This paper mainly relates to the real polychlorinated biphenyl (PCB)-contaminated soil flushing process, in which an aqueous solution of anionic surfactant was passed through sandy soil having an average concentration 34.3 mg/kg of dry matter. The goal of the treatment was to decrease the PCB concentration in the soil to less than 10 mg/kg, which is a limiting value if the soil is to be used in the field of civil engineering. The laboratory part was focused on the demonstration of the suggested method for estimating the CMC value of the surfactant used for leaching the PCBs from the soil to the solution. The estimate was based on a set of batch experiments carried out with the same soil as the soil used for the pilot-scale experiments. Theoretically, all effects affecting the CMC should be considered in an estimated value. The experimental facility used for the pilot-scale demonstration consisted of a steel column (3 m in length, 1.5 m in diameter) containing 1.7 m 3 of polluted soil and a liquid circulation system, by which an aqueous solution of a surfactant was supplied to the soil. Spolapon AOS 146 (anionic surfactant) solution (40 g/L) was passing through the soil column for 2.5 months. The concentration of the surfactant and PCBs in the aqueous soil extract was monitored during this time period. The final PCB concentration profile in the soil was determined after stopping the liquid flow. After passing through the soil, the PCBs containing the aqueous extract was pumped out from the steel column bottom to a treatment unit, where it was processed by coagulation. The final PCB concentration profile in the soil was compared with the results of the theoretical model, which is also described in the paper. The time necessary to reach the limit demanded was estimated to move within the range from 6 to 12 months.

Rheological properties of wormlike micelles formed in the sodium oleate/trisodium phosphate aqueous solution

Aqueous solution of anionic surfactant, sodium oleate (NaOA), was studied by means of steady-state shear rheology and dynamic oscillatory technique. The system of NaOA/Na 3PO 4 showed high viscosity, strong viscoelasticity and good ability of countering Ca 2+, Mg 2+. The Maxwell model and Cole–Cole plot were applied to study the dynamic viscoelasticity of wormlike micelles. The microstructures of the wormlike micelles were characterized by FF-TEM.

Surfactant‐Enhanced Carbon Regeneration in a Vapor‐Phase Application

Coal‐based granular activated carbon (GAC) is saturated with trichloroethylene (TCE) by passing air through a fix bed adsorber. In surfactant‐enhanced carbon regeneration, an aqueous solution of anionic surfactant, sodium dodecyl sulfate (SDS), is passed through the bed to induce desorption of TCE. More than 95% of the sorbed TCE was removed in the desorption operation with a 0.1 M SDS solution at a superficial flow rate of 1 cm/min. The desorption rate of TCE from pores of GAC is limited by pore diffusion and not significantly affected by either the concentration of SDS in the regenerant (when well above the critical micelle concentration) or its flow rate. From the breakthrough curve of a subsequent adsorption cycle without a flushing step following the desorption, only 7% of the virgin carbon effective adsorption capacity is observed for the regenerated carbon. With a water flushing step following the regeneration step, the effective adsorption capacity is significantly improved to about 15% of that of virgin carbon. Increased temperature of the flushing water also enhances the effective adsorption capacity of the regenerated GAC. Separate batch adsorption‐desorption isotherms of SDS on GAC support the enhanced desorption of SDS at elevated temperatures. The drastic reduction in the effective adsorption capacity of regenerated GAC results from the residual SDS remaining in the pores of GAC as confirmed by thermal gravimetric analysis. Both the regeneration and water flush steps are rate limited under conditionsused here.

Rheological properties of wormlike micelles in sodium oleate solution induced by sodium ion

Aqueous solutions of anionic surfactant, sodium oleate (NaOA), have been studied by means of steady-state shear rheology and dynamic oscillatory technique. The micellar structure can be changed upon the addition of NaCl, Na 2CO 3 and NaCl/NaOH while NaOA concentration is maintained at 0.060 M. These systems except NaOA/NaCl show high viscosity and strong viscoelasticity. The hydroxide ion is very important for the formation of wormlike micelles. The anions of salts also have effect on the rheological properties of wormlike micelles. Three parameters: intersection frequency ω i, plateau modulus G 0 and relaxation time τ are also discussed. The Maxwell model and Cole-Cole plot are applied to investigate the dynamic viscoelasticity of wormlike micelles. Variation in surfactant packing parameter R P can be used to explain the change of rheology and microstructure of the micelles.

Detachment of Oil Drops from Solid Surfaces in Surfactant Solutions: Molecular Mechanisms at a Moving Contact Line

Here, we present experimental data and a theoretical model for the dynamics of detachment of hexadecane drops from a solid substrate (glass plate) in aqueous solutions of anionic surfactant and salt, at various temperatures. The influence of the experimental conditions on the motion of the three-phase contact line is investigated. We found indications that water molecules can propagate by lateral diffusion in a thin layer on the surface of the solid plate. The driving force of the detachment process, viz., the imbalance of the interfacial tensions at the contact line, is engendered by the water penetration, while the line friction force compensates this imbalance and determines the stationary speed. Excellent agreement between theory and experiment is achieved. The present study specifies the parameters that can be used to quantitatively characterize the rate of drop detachment, determines the values of these parameters at various experimental conditions, and indicates tools for control of the investigated spontaneous process.

Thermodynamic Model of Surfactant Adsorption on Soft Liquid Crystal Interfaces

The Gibbs adsorption isotherm for planar liquid crystal/fluid interfaces is derived using the anisotropic Gibbs-Duhem equation. The Gibbs adsorption isotherm for planar interfaces is used to analyze the adsorption-driven orientation transition in aqueous solutions of anionic surfactants in contact with rodlike uniaxial nematic liquid crystal films. In qualitative agreement with experiments, the model predicts that, as the surfactant concentration increases, the tangential (planar) average molecular orientation of the liquid crystal with respect to the interface undergoes a transition to a normal (homeotropic) orientation. The anchoring coefficient or strength of anisotropic component of the interfacial tension is shown to depend on the surfactant's concentration. Analyzing the response to addition of a co-cation, the model reveals that, as the fractional coverage of the surfactant's chains increases, the interpenetration of liquid crystal molecules between the adsorbed surfactant tails promotes the orientation transition; at even higher surfactant chain concentrations, interpenetration is hindered because of lack of available space and a random surface orientation emerges. Thus, for aqueous surfactant solutions in contact with nematic liquid crystals, increasing the surfactant concentration leads to the following interfacial liquid crystal orientation transition cascade, planar orientation --> homeotropic orientation --> random orientation, which can lead to new sensor capabilities and surface structuring processes.

Heat Capacity of Transfer of (Ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 from Water to the Aqueous Anionic Surfactant Solutions at 298 K. A Quantitative Treatment

Heat capacities of transfer (DeltaCpt) of unimeric (ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 from water to the aqueous surfactant solutions as functions of the surfactant concentrations (mS) were determined at 298 K. The surfactants investigated are sodium hexanoate, sodium heptanoate, sodium octanoate, sodium undecanoate, and sodium dodecanoate. For short alkyl chain surfactants, the profiles of the DeltaCpt versus mS curves show maxima and minima; for long alkyl chain surfactants, the maximum becomes sharper and moved to lower mS values whereas the minimum tends to disappear. These experimental trends are different from those of the enthalpy in agreement with the fact that heat capacity, being the derivative of enthalpy with respect to temperature, reflects additional terms generated by temperature change on the equilibria in solution. On the basis of a thermodynamic model recently proposed by us for properties first derivatives of Gibbs free energy, a quantitative treatment of the experimental data was done. Such an approach assumes that even in the dilute surfactant region monomers of surfactant associate with unimeric copolymer generating surfactant-copolymer aggregation complexes and, whenever the surfactant achieves the conditions for the micellization, the formation of copolymer-micelle mixed aggregates takes place. The equation derived for the heat capacity of transfer is more complex than that for the enthalpy because it contains five additional terms due to the shift of the equilibria induced by the temperature change. It turned out that these contributions, evaluated by using the equilibrium constants and the associated enthalpies, cannot be neglected for a quantitative treatment of the experimental data. The minimizing procedure provided the heat capacity changes for the formation of the surfactant-copolymer aggregation complexes and the copolymer-micelle mixed aggregates.

Dewetting behavior of aqueous cationic surfactant solutions on liquid films.

Previous experimental work has shown that the spreading of a drop of aqueous anionic surfactant solution on a liquid film supported by a negatively charged solid substrate may give rise to a fingering instability (Afsar-Siddiqui, A. B.; Luckham P, F.; Matar, O. K. Langmuir 2003, 19, 703-708). However, upon deposition of a cationic surfactant on a similarly charged support, the surfactant will adsorb onto the solid-liquid interface rendering it hydrophobic. Water is then expelled from the hydrophobic regions, causing film rupture and dewetting. In this paper, experimental results are presented showing how the surfactant concentration and film thickness affect the dewetting behavior of aqueous dodecyltrimethylammonium bromide solutions. At low surfactant concentrations and large film thicknesses, the film ruptures at a point from which dewetting proceeds. At higher concentrations and smaller film thicknesses, the ruptured region is annular in shape and fluid moves away from this region. At still higher concentrations and smaller film thicknesses, the deposited surfactant forms a cap at the point of deposition that neither spreads nor retracts. This variation in dewetting mode is explained by considering the relative Marangoni and bulk diffusion time scales as well as the mode of assembly of the surfactant adsorbed on the solid surface.

Unstable Spreading of Aqueous Anionic Surfactant Solutions on Liquid Films. Part 1. Sparingly Soluble Surfactant

Experimental work has shown that the spreading of aqueous surfactant solutions on a thin liquid film may be accompanied by a fingering instability, the characteristics of which are dependent on the initial film thickness and surfactant concentration. Experimental results are presented showing how these parameters affect the fingering instability for a sparingly soluble anionic surfactant, sodium di-2-ethyl-hexyl sulfosuccinate. It is found that at surfactant concentrations well below the critical micelle concentration (cmc) stable spreading occurs but at concentrations in the vicinity of the cmc fingering develops behind the spreading front on water films as thick as 100 μm. At surfactant concentrations greater than the cmc, there is stable spreading with the formation of a central “disk” at lower thicknesses while fingering is observed at a higher thickness. Increasing the initial film thickness results in greater instability onset times and wider fingers, whereas increasing surfactant concentration give...

Unstable Spreading of Aqueous Anionic Surfactant Solutions on Liquid Films. 2. Highly Soluble Surfactant

The spreading of a surfactant solution across a thin water film may be accompanied by a fingering instability developing behind the spreading front. In this paper, the role of solubility on this instability is investigated by conducting spreading experiments using highly soluble surfactant solutions of sodium dodecyl sulfate over a range of concentrations on water films ranging from 25 to 100 μm in thickness. It is found that at surfactant concentrations up to and around the critical micelle concentration, spreading is largely accompanied by fingers upstream of the spreading front. In comparison with sparingly soluble AOT solutions (sodium di-2-ethylhexyl sulfosuccinate) studied in part 1 of this series, the instability becomes apparent sooner and the fingers are more pronounced and branched. Above the cmc, the instability takes a different form on thinner films, which was not noted in the sparingly soluble case, while fingering develops on thicker films.

Influence of the structure of amphiphilic anions on the Krafft temperature of micellar solutions of anionic surfactants

The influence of the structure of surfactants on the Krafft temperature Tk was studied for aqueous solutions of anionic surfactants containing the sulfate and sulfonate head groups, the hydrophilic (H) and lipophilic (L) fragments in amphiphilic anions, and various polar and C8—C18 hydrocarbon groups. The best statistical quality was obtained for the model with separate account of the effect of the H and L structural fragments on the Tk value.

Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach

On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid–liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0–10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed.

A criterion for buoyancy induced drop detachment based on an analytical approximation of the drop shape

The detachment of small oil drops from metal surfaces placed in an aqueous medium is examined. It is observed that buoyancy induced drop break-up and not ‘roll-up’ is responsible for most of the oil removal. The aqueous phases used in this study are concentrated aqueous solutions of anionic surfactants and the oils used are lighter than water. Roll-up occurs but is not able to cause detachment of the oil drop completely on its own. A quantitative view of the above system is developed leading to a stability criterion. This stability criterion can be used to predict buoyancy induced partial drop detachment. The quantitative criterion is developed using an analytical approximation for the pendant drop profile. This approximation results in much smaller errors as compared with the ‘spherical cap’ assumption. The quantitative criterion is used to predict interfacial tensions (IFT), density differences and three phase contact angles that are required to induce partial drop removal from solid surfaces. Predictions from the equations match the observations. The above criterion is used to compute the stability boundaries for different drop volumes in the space defined by the above variables.