Cmc Of Sodium Dodecyl Sulfate Research Articles

Kinetic study of Ru(III) – catalyzed oxidation of L-phenylalanine by hexacyanoferrate(III) in an anionic surfactant medium

Abstract The kinetic investigation of Ru(III) promoted oxidation of L-phenylalanine (L-PheAla) by [Fe(CN)6]3− has been performed in anionic sodium dodecyl sulfate (SDS) micellar medium by recording the decrease in absorbance at 420 nm corresponding to [Fe(CN)6]3− using an UV–visible spectrophotometer. Using the pseudo-first-order condition, the course of the reaction was studied as a function of [Fe(CN)6 3−], ionic strength, [OH−], [SDS], [Ru3+], [L-PheAla] and temperature by changing one variable at a time. The results exhibit that [OH−], [SDS], and [L-PheAla] are the crucial parameters that have an appreciable influence on the reaction rate. The reaction exhibits first-order kinetics in concentration ranges of Ru(III), [Fe(CN)6]3− and at low [L-PheAla] and [OH−] concentrations. The incremental trend observed in the reaction rate with electrolyte concentration shows a positive salt effect. The reaction rate is almost 10 times faster in SDS micellar medium than in aqueous medium. [Fe(CN)6]3− has no appreciable effect on the CMC of SDS, since the polar head of SDS and [Fe(CN)6]3− are both negatively charged. The K+ obtained from K3[Fe(CN)6] and KNO3 decreases the repulsion between the negatively charged heads of the surfactant molecules, which decreases the CMC of SDS. The activation parameters also support the outer-sphere electron transfer mechanism.

Interaction of methylene blue with SDS in the premicellar solution of CPC in the aqueous and methanol-water system

Interactions between sodium dodecyl sulfate (SDS) and methylene blue (MB) have been studied in presence of cetylpyridinium chloride (CPC) in aqueous and methanol-water binary solvents via conductometric and tensiometric methods. The experiment was conducted to see the possibility of a synergistic effect of the SDS+CPC system and changes in the interactional behavior of SDS with MB in presence of CPC. The value of the molecular interaction parameter for micellization (βM) was found to be negative from the experimental results and the value of |βM| was found to be greater than ln(CMCSDS / CMCCPC), which didn’t describe synergism completely but indicated the strong striking interactions between the oppositely charged surfactants. However, the CMC of the SDS+CPC system was found to be very low as compared to the CMC of SDS alone. This result of CMC based on striking interactions between oppositely charged surfactants was used to calculate various parameters like Gibb’s free energy of micellization (∆Gmo), surface excess(Γmax), minimum surface area (Amin), surface pressure πCMC, standard free energy of adsorption (∆Gadso), pC20, minimum surface free energy (Gmins), packing parameter (P) and association equilibrium constant (K). The addition of methanol as a cosolvent enhances the CMC and α value of the SDS+CPC as well as the SDS+CPC-MB system. Correlation of ∆Gmo with different solvent parameters namely Gordon parameter (G), Reichardt's parameter (ET (30)), viscosity (ηo), and solvophobic parameter (SP) has also been evaluated.

Sodium dodecyl sulfate modulates the structure and rheological properties of Pluronic F108-poly(acrylic acid) coacervates).

Micelles formed within coacervate phases can impart functional properties, but it is unclear if this micellization provides mechanical reinforcement of the coacervate whereby the micelles act as high functionality crosslinkers. Here, we examine how sodium dodecyl sulfate (SDS) influences the structure and properties of Pluronic F108-polyacrylic acid (PAA) coacervates as SDS is known to decrease the aggregation number of Pluronic micelles. Increasing the SDS concentration leads to larger water content in the coacervate and an increase in the relative concentration of PAA to the other solids. Rheological characterization with small angle oscillatory shear (SAOS) demonstrates that these coacervates are viscoelastic liquids with the moduli decreasing with the addition of the SDS. The loss factor (tan δ) initially increases linearly with the addition of SDS, but a step function increase in the loss factor occurs near the reported CMC of SDS. However, this change in rheological properties does not appear to be correlated with any large scale structural differences in the coacervate as determined by small angle X-ray scattering (SAXS) with no signature of Pluronic micelles in the coacervate when SDS concentration is >4 mM during formation of the coacervate, which is less than that observed (6 mM SDS) in initial Pluronic F108 solution despite the higher polymer concentration in the coacervate. These results suggest that the mechanical properties of polyelectrolyte-non-ionic surfactant coacervates are driven by the efficicacy of binding between the complexing species driving the coacervate, which can be disrupted by competitive binding of the SDS to the Pluronic.

Exploring the effect of hydrophobic ionic liquid on aggregation, micropolarity and microviscosity properties of aqueous SDS solutions

Ionic liquid (IL)-modified surfactant systems have versatile applications in several technological areas. Therefore, it is utmost need to achieve full understanding of interactions existing in such systems before their further uses. Here, the effects of IL, 1-ethyl-3-methylimidazolium hexafluorophospahte, [emim][PF6] on the physicochemical properties of aqueous sodium dodecyl sulfate (SDS) solutions has been studied using multi-technique approach. Various micellar parameters such as critical micelle con-centration (cmc), degree of counter ion dissociation (α), aggregation number (Nagg) as well as some thermodynamic parameters such as standard free energy of micellization (G°m), standard enthalpy of micellization (H°m) and standard entropy of micellization (S°m) and surface properties from surface tension measurement have been evaluated. A significant decrease in cmc, and increase in degree of counter ion dissociation along with increase in Nagg is observed. The aggregation behaviour of SDS is also studied in presence of ILs having different alkyl chain length in their imidazolium cations. A decrease in CMC of SDS observed, and trend of decrease in CMC is reported as [hmim][Cl] > [bmim][PF6] > [emim][PF6]. The micropolarity and microviscosity of micellar media are accessed with fluorescence probe studies. The effect of chain length of IL cation has been also explored on aggregation behaviour. The FTIR technique is employed to evaluate possible interactions between SDS and IL [emim][PF6] molecules, the information regarding size of SDS micelle in presence of IL [emim][PF6] has been explored by DLS technique.

Influence of ammonium salts on the interaction of fluoroquinolone antibiotic drug with sodium dodecyl sulfate at different temperatures and compositions

The interaction between sodium dodecyl sulfate (SDS) and an antibiotic drug, ciprofloxacin hydrochloride (CPFH) has been carried out by conductometric measurement at various temperatures from 298.15 K to 318.15 K. The critical micelle concentration (cmc) values of SDS/SDS+CPFH mixture were attained to be reduced in the electrolytes medium. The effect on the cmc reduction is higher in case of ammonium carbonate than ammonium chloride. The cmc values of SDS/SDS+CPFH mixture follow U-shaped behavior with temperature in water and ammonium chloride and reversed U-shaped in ammonium carbonate solution. In the existence of CPFH, the cmc of SDS reduces in aqueous medium but enhances in the electrolytes medium. The extent of micelle ionization (α) was found to be enhanced with the increase of concentration of CPFH in aqueous medium and in ammonium chloride medium at a lower temperature. The α values follow inverted U-shaped in ammonium carbonate medium. The estimated values of ΔGmo for distinct SDS, as well as SDS+CPFH mixtures, were obtained to be negative in entire cases illustrating the spontaneity of micellization. The magnitudes of ΔHmo, ΔSmo and thermodynamic parameters of transfer have been evaluated and discussed in details.

Critical Micelle Concentrations of Sodium Dodecyl Sulfate and Cetyltrimethylammonium Bromide Mixtures in Binary Mixtures of Various Salts at Different Temperatures and Compositions

By conductivity method were examined the aggregation behavior of cationic amphiphile–cetyltrimethylammonium bromide (CTAB) and anionic amphiphile–sodium dodecyl sulfate (SDS) mixtures in binary mixtures of various salts. The values of critical micelle concentration (cmc) of SDS–CTAB mixtures lie between the cmc values of the pure amphiphiles. With temperature increasing the cmc values decrease first and then enhance with further rise of the temperature. The observed cmc of the SDS–CTAB mixed systems in attendance of binary mixture of salts was obviously less as compared to aqueous solution. The degree of counterion dissociation along with cmc value was utilized to evaluate different thermodynamic parameters. The values of interaction parameters and excess free energy were found to be negative in all cases. All results obtained reveal the strong interaction between the studied amphiphiles.

Role of ammonium ion on the aggregation and adsorption properties of sodium dodecylsulfate

ABSTRACTThe role of mixed counterion toward the aggregation behavior of sodium dodecylsulfate (SDS) is quantified by determining the critical micelle concentration (cmc) of SDS micelle in the presence of added NH4Cl salt. The dependence of cmc of SDS on added salt is explained in the light of the modified Corrin–Harkins equation and the nonlinearity of this plot is shown due to the exchange of Na+ ion by added ion. The aggregation number (N) of SDS micelle is also calculated using the steady-state fluorescence method, where sudden change in N value was observed in two different concentration regions of the modified CH plot. Furthermore, the hydrodynamic diameter (dH) of dodecyl sulfate micelles was determined using the dynamic light scattering method. In scattering studies, a sharp change in the value of dH occurred at around 50 mM of added salt, which might hint toward the shape change of dodecyl sulfate micelle. The surface excess values of SDS in the presence of mixed inorganic counterion are also calculated in the light of the Gibbs adsorption isotherm.

A novel approach for methylene blue removal by calcium dodecyl sulfate enhanced precipitation and microbial flocculant GA1 flocculation

A novel approach was proposed for the removal of methylene blue (MB), a soluble cationic dye, from aqueous solution by calcium dodecyl sulfate (Ca(DS)2) enhanced precipitation which was based on the solubilization of sodium dodecyl sulfate (SDS) on MB and Ca2+ effect on SDS micelles, and microbial flocculant GA1 (MBFGA1) flocculation. The independent and interactive effects of factors, such as SDS, Ca2+ and MBFGA1 dosages, on the MB removal and interaction between SDS and Ca2+ were investigated. The response surface methodology (RSM), environmental scanning electron microscope (ESEM) and energy dispersive spectrometer (EDS) analysis were employed to discuss the interaction mechanism between SDS and Ca2+, and MB removal mechanism. The results showed that MB and SDS removal efficiency could reach 98.63% and 88.97%, respectively, with pH (10), MB (50mg/L), SDS (8mM), Ca2+ (5mM) and MBFGA1 (4mL/L). Under the optimal conditions, residual SDS and Ca2+ concentrations in the upper phase were 0.88mM and 1.27mM, respectively, which reached the Ksp of Ca(DS)2. The concentration consumption ratio between SDS and Ca2+ was 2.0. The interaction between SDS and Ca2+ was depended on the SDS-Ca2+ concentration ratio in aqueous solution rather than the CMC of SDS. When Ca2+ concentration was relatively sufficient, SDS micelles containing the solubilized MB (SDS-MB micelles) would disassemble to generate MB loaded Ca(DS)2 particles (CDS-MB particles) which would be flocculated by MBFGA1. Whereas, when SDS concentration was superfluous relatively, SDS micelles formed in the upper phase would redissolve the CDS-MB particles in flocs.

Preparation, Characterization and Measurement of CMC of SDS, CTAB and Tween 80 Based Self-Assembled Aggregates in W/O and O/W Microemulsions as Systems for Preparing Nanomaterials

Series of water in oil (w/o) composition of microemulsions were prepared from systems with sodium dodecyl sulphate (SDS), 1-butanol, cyclohexane, water; tween 80, 1-butanol, cyclohexane, water and cetyltrimethylammonium bromide (CTAB), 1-butanol, cyclohexane, water; at varying water to surfactant mole ratio, w0 and oil in water (o/w) composition of SDS and CTAB based microemulsions were made at reconcile with composition of w/o microemulsions. Micelles and reverse micelles are dominant form of self-assembled aggregates in o/w microemulsions and w/o microemulsions respectively. The ability of these aggregates to solubilize water had been employed for the detection of the critical micellization concentration, cmc for micelles and reverse cmc for reverse micelles. The reverse cmc values are smaller (0.204-0.293M) than the micellar cmc (0.4605-0.607M) was observed.1-butanol as a stabilizer provided information of the systems to give thermodynamically stable transparent w/o and o/w microemulsion due to its low linear thickness. Specific conductance, density and aggregation number had been used to characterize SDS and CTAB based microemulsions and the microemulsions prepared by non-ionic surfactant, tween 80 were characterized by only density measurement. Lower conductance and density are characteristics for w/o microemulsions having high 1-butanol content while in o/w microemulsions leads higher conductance and density. Steady-State Fluorescence Quenching method had been employed to determine the aggregation number, N of the organized self-assembled aggregates. The aggregation number of the aggregates in the microemulsions varied with composition of the microemulsions and depends only on the concentration of surfactant present in the systems. Aggregation number had been found to increase as the number of micellar aggregates increases. However, an increase in the number of reverse micellar aggregates in the system brought about gradual decrease of the aggregation number. As the quenching process of SDS based aggregates was very effective, however that of CTAB was less pronounced, the aggregation number of SDS based aggregates had been found to be comparatively lower than that of CTAB under similar experimental conditions. The results obtained show that N values which range 78–101 for SDS based aggregates and range 99-160 for CTAB based aggregates show a linear relationship with the concentration of surfactant. Detailed analysis of the conductivity, density and aggregation number, it can be tuned by changing composition of microemulsions and suitable compositions of microemulsions must be employed for the preparation of nanomaterials.

Solubilization of 1-hexanol in aqueous solutions of sodium dodecyl sulfate at pressures up to 140 MPa: partial molar volumes, compressibilities, and partition coefficients.

Partial molar volumes and partial molar compressibilities of aqueous solutions of sodium dodecyl sulfate (SDS) and 1-hexanol at pressure up to 140 MPa have been determined. For aqueous SDS solutions the partial molar compressibility increases with pressure below the cmc and decreases with pressure above the cmc. The partial molar compressibility of aqueous 1-hexanol increases with pressure. The increased partial molar compressibility reflects that the structure of water is gradually broken down by increased pressure. Thus, the negative effect of electrostriction around the charged parts of SDS decreases as do the effects of hydrophobic hydration around the CH2 groups. In the micellar state the compressibility of the aggregate is the main factor, becoming less compressible as pressure increases. The cmc of SDS, as determined by speed of sound measurements, increases with pressure and goes through a shallow maximum at about 110 MPa. When 1-hexanol is added to SDS solutions, it will be partitioned between the aqueous and micellar (pseudo) phases. The partition coefficient has been determined from partial molar compressibilites, and it appears to decrease with pressure, reach a minimum around 80 MPa, and then increase, though the change with pressure is small.

Micellization behaviour of sodium dodecyl sulphate in presence and absence of sodium sulphate and zinc sulphate in distilled water by surface tension measurement

The accurate measurements of surface tension of sodium dodecyl sulphate (SDS) in distilled water and in presence of 0.01M Na2SO4 and 0.01M ZnSO4 at room temperature were reported by drop weight method using a stalagmometer. The critical micelle concentration (cmc) of sodium dodecyl sulphate (SDS) in distilled water was obtained higher than in presence of Na2SO4 and ZnSO4. The decrease of cmc of sodium dodecyl sulphate in the presence of salts has been discussed. DOI: http://dx.doi.org/10.3126/bibechana.v11i0.10383 BIBECHANA 11(1) (2014) 79-85

Aggregation of sodium dodecylsulfate in aqueous nitric acid medium

Nitric acid medium is invariably used for nitration of organic molecules. Although surfactants are known to influence reaction rates, little is known about the aggregation behavior of surfactants in nitric acid medium. Micellization characteristics of sodium dodecylsulfate (SDS) in aqueous nitric acid are investigated in this work by using the conductance method. The critical micelle concentration (cmc) and the aggregation number were also determined by the surface tension and the steady-state fluorescence methods, respectively. This study reveals that in acidic medium SDS exhibits both normal and unusual conductivity behaviors. Equations developed on the basis of the mixed electrolyte model, Debye–Hückel–Onsager approach, and the pseudophase ion-exchange model successfully simulate the conductivity data. The exchange of sodium and hydrogen counterions at the micellar surface has no significant effect on the cmc of SDS. Acid concentration, surfactant concentration, and cmc control the competitive binding of sodium and hydrogen counterions. Analysis of conductivity data revealed hydrolysis of about 12% SDS when [HNO3]⩾0.02moldm−3. Hydrolysis of SDS has been confirmed by nitrating some of the substituted phenols. It has been predicted that SDS+aqueous HNO3 medium with [HNO3]⩾0.02moldm−3 may be used as a green medium for nitration.

Effect of Pharmaceutically Important Cosolvents on the Interaction of Promethazine and Trifluopromazine Hydrochloride with Sodium Dodecyl Sulfate Micelles

The present study is an attempt to gain a better understanding of the characteristics of binding of phenothiazine drugs; promethazine hydrochloride, and triflupromazine hydrochloride to sodium dodecyl sulfate micellar system in the presence of pharmaceutically important cosolvents, such as ethanol, ethyleneglycol, and propyleneglycol. The interactions of promethazine and triflupromazine hydrochloride with anionic surfactant sodium dodecyl sulfate in the absence and presence of various concentrations of cosolvents have been studied by absorption spectroscopy as a function of surfactant concentration ranging from the premicellar to postmicellar region at 298 K. The binding tendency of promethazine and triflupromazine hydrochloride to sodium dodecyl sulfate micelles decreased with the concentration of cosolvents increased. The addition of cosolvents increased the CMC of sodium dodecyl sulfate and at a certain concentration totally inhibited the micellization. The inhibitory effect of cosolvents on binding of promethazine and triflupromazine hydrochloride to micelles followed the order as; water > ethyleneglycol > propyleneglycol > ethanol. Polarity of the micellar microenvironment and probable location of promethazine and triflupromazine hydrochloride were also discussed in different micellar media.

Suppression and Regeneration of Camphor-Driven Marangoni Flow with the Addition of Sodium Dodecyl Sulfate

We investigated the Marangoni flow around a camphor disk on water with the addition of sodium dodecyl sulfate (SDS). The flow velocity decreased with an increase in the concentration of SDS in the aqueous phase, and flow was hardly observed around the critical micelle concentration (cmc), because SDS reduced the driving force of Marangoni flow. However, the flow velocity increased with a further increase in the concentration of SDS. Thus, the Marangoni flow is maximally inhibited around the cmc of SDS. In this paper, we concluded that the regeneration of Marangoni flow originates from an increase in the dissolution rate of camphor into the SDS aqueous solution.

Manipulation of Concentration-Conductivity Data of Sodium Dodecyl Sulphate and Sodium Dodecylbenzene Sulphonate in KCl Solution in Relation to Micellisation Parameters

The conductivity of sodium dodecyl sulphate (SDS) and sodium dodecylbenzenesulphonate (SDBS) has been studied in varying concentrations (0-5 mM) of aqueous KCl solution at 25oC. Data analysis was based on the conventional treatment of conductivity-concentration data, differential, and integration methods with the aim of knowing the best method. As expected, the conductivity increased with an increase in surfactant concentration; the plot of which showed a kink at critical micelle concentration, cmc (i.e. point of aggregation). The results showed no apparent relationship between the degree of counterion binding, β and [KCl]; and an inverse relationship between the cmc values and [KCl]. β was within 0.4-0.6 for SDS and 0.1-0.3 for SDBS. The cmc of SDS decreased from ca. 8 to 6 mM and that of SDBS from ca. 2 to 1 mM as the [KCl] increased from 0-5 mM. These values are in mutual agreement irrespective of the method used. It was confirmed that in the absence of KCl, values obtained from the integration method were more consistent with those reported in the literature; therefore this method is recommended as the best method for determination of micellisation parameters provided the process is followed by conductivity measurements.

Experimental and molecular dynamics investigation into the amphiphilic nature of sulforhodamine B.

Sulforhodamine B (SRB), a common fluorescent dye, is often considered to be a purely hydrophilic molecule, having no impact on bulk or interfacial properties of aqueous solutions. This assumption is due to the high water solubility of SRB relative to most fluorescent probes. However, in the present study, we demonstrate that SRB is in fact an amphiphile, with the ability to adsorb at an air/water interface and to incorporate into sodium dodecyl sulfate (SDS) micelles. In fact, SRB reduces the surface tension of water by up to 23 mN/m, and the addition of SRB to an aqueous SDS solution induces a significant decrease in the cmc of SDS. Molecular dynamics simulations were conducted to gain a deeper understanding of these findings. The simulations revealed that SRB has defined polar "head" and nonpolar "tail" regions when adsorbed at the air/water interface as a monomer. In contrast, when incorporated into SDS micelles, only the sulfonate groups were found to be highly hydrated, suggesting that the majority of the SRB molecule penetrates into the micelle. To illustrate the implications of the amphiphilic nature of SRB, an interesting case study involving the effect of SRB on ultrasound-mediated transdermal drug delivery is presented.

Physicochemical and Conformational Studies on BSA−Surfactant Interaction in Aqueous Medium

In this paper, results of physicochemical studies on the interaction of bovine serum albumin (BSA) with alkyltrimethylammonium bromide (ATAB), pentaethylene glycol mono-n-dodecyl ether (C12E5), and sodium dodecyl sulfate (SDS) under the experimental conditions of phosphate buffer at pH 7 in the presence of 10 mM sodium bromide (NaBr), maintaining the ionic strength of the overall solution at micro = 0.015 M, have been presented and discussed. Here, BSA-ATAB corresponds to a polyion-surfactant system bearing opposite charges. BSA precipitated out of the solution on addition of ATAB solution over a certain range of ATAB concentration, the concentration range being dependent on the particular member of the ATAB family. In our earlier reports on the precipitation of oppositely charged polymer-surfactant, the tensiometric profile for surfactant addition in polymer solution differed significantly from that expected from addition of surfactant in the dispersion medium. In the present study, the precipitation process could hardly affect the smoothness of the tensiometric profile. This indicates the interaction process is operative in bulk solution. Microcalorimetric profiles also evidenced an extra hump in the interaction profile at lower surfactant concentrations, without much affecting the dilution enthalpograms beyond micellization. This interaction appeared unimodal and the extent of interaction increased with increasing tail length of ATAB, evidencing the hydrophobic effect to be an important factor. Addition of salt (NaBr) also affected the nature of interaction: at lower concentration of NaBr, the interaction was mildly assisted, whereas 50 mM NaBr fairly assisted the interaction. The nonionic surfactant C12E5 modestly interacted with BSA. The anionic amphiphile SDS, on the other hand, interacted with BSA in two distinctly different stages, as evidenced from the tensiometric profile. The complexity of the BSA-SDS tensiometric isotherm compared to that of BSA-ATAB arose from the presence of cationic binding sites adjacent to hydrophobic patches of BSA in its native state, so that electrostatic and hydrophobic interactions can cooperatively operate side by side. The interfacial saturation occurred at a lower concentration in the presence of BSA compared to the normal cmc of SDS under identical solution conditions in the absence of BSA, which was slightly delayed for nonionic C12E5. The multitechnique approach evidenced that different experimental techniques probe different physicochemical phenomena and an attempt to show the concurrence of the break points in different techniques is only diluting the essence of this area.

Cationic Amphiphilic Polyelectrolytes and Oppositely Charged Surfactants at the Silica−Aqueous Interface

The influence of sodium dodecyl sulfate (SDS) on the interfacial behavior of two amphiphilic polyelectrolytes, which are copolymers of the cationic monomers triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride, at the silica-aqueous interface was studied. The fraction of amphiphilic monomers was varied, where 0DT, 40DT, and 80DT contained 0, 40, and 80 mol % monomers with dodecyl side chains, respectively. We used in situ ellipsometry to follow the kinetics of adsorption, in terms of adsorbed amount and adsorbed layer thickness, as well as the response of the adsorbed layers to changes in ionic strength and surfactant concentration. Different results were obtained when surfactant was added to the preadsorbed layers compared to the cases when complexes were preformed in the solution prior to the adsorption. In the whole range of concentrations studied, SDS interacts with 40DT and 80DT noncooperatively, whereas for 0DT cooperativity of binding is observed. The amount adsorbed increased significantly as the SDS concentration was close to the cmc. At high SDS concentrations, a lowering of the layer density was observed. For the amphiphilic polyelectrolytes, 40 DT and 80DT, no desorption from the interface was detected for the range of SDS concentrations studied, while 0DT features a maximum in adsorbed amount at concentrations close to the cmc of SDS. Adsorption of 40DT and 80DT from their mixtures with SDS is found to be path dependent with respect to the variation in SDS concentration, where the reversibility decreases with increasing SDS concentration above the expected charge neutralization point. The coadsorption of 80DT and SDS is highly irreversible with respect to changes in the ionic strength within the time scale of the experiment. In this study, we attempt to illustrate both general mechanisms and specific effects. With regard to the general behavior, it is important to note the charge regulation of both the silica surfaces and the polyion/surfactant complexes; an interplay between the two charge-regulating effects is the key to understanding our observations.

Removal of copper ions and dissolved phenol from water using micellar-enhanced ultrafiltration with mixed surfactants

A laboratory study was conducted to evaluate the effects of composition and concentration of mixed anionic/nonionic surfactants on the efficiency of a micellar-enhanced ultrafiltration (MEUF) operation in removing metal ions/organic solutes from aqueous solutions. Based on the analysis of surface tensions and micelle sizes, it was found that for mixed sodium dodecylsulfate (SDS)/Triton X-100 surfactants, the critical micelle concentration (cmc) was significantly lower than that of SDS and mixed micelles formed. The mixed surfactant system was then applied in a cross-flow mode of MEUF, in which the concentration polarization can be neglected, to remove Cu 2+ from aqueous solutions. With a surfactant concentration of 10 mM, the Cu 2+ rejection was negligible by using pure Triton X-100 and increased with increasing SDS mole fraction with a value as high as 85%, which suggests that the rejection of Cu 2+ was due to the electrostatic attraction between Cu 2+ and SDS. Furthermore, pronounced Cu 2+ rejection was obtained for a 5 mM SDS solution, which was attributable to a decrease in the cmc of SDS by the existence of Cu 2+. When the MEUF technique was applied to remove Cu 2+ and phenol simultaneously from aqueous solutions, the Cu 2+ rejection was slightly enhanced in the presence of phenol. However, the rejection of phenol was comparatively low, ∼27%, which may be caused by its relatively hydrophilic characteristic.

Swelling of poly(ethylene oxide) gel in aqueous solutions of sodium dodecyl sulfate with added sodium chloride

The swelling behavior of poly(ethylene oxide) (PEO) gels in aqueous solutions of sodium dodecyl sulfate (SDS) with and without NaCl was investigated. In the absence of NaCl, PEO gels with different degrees of cross-linking began to swell from a concentration lower than the critical micelle concentration (cmc) of SDS, then showed sigmoidal enhancements of swelling in a higher SDS concentration region until the degrees of swelling reached maximum values. The SDS concentration at which the swelling began to appear was in reasonable agreement with the critical aggregation concentration (cac) value reported for the aqueous PEO system. For the cases where NaCl was present, the swelling behavior of PEO gel was different from that when NaCl was absent in the following way. The concentrations where the swelling begins to appear, and hence those where the degree of swelling rises steeply, decreased with an increase in NaCl concentration. The ultimate degrees of swelling at higher concentration regions also decreased with an increase in the NaCl concentration. The lowering of the SDS concentrations at which the PEO gel began to swell is in line with the decreases in the cmc of SDS solutions containing NaCl and also with the decreases in the cac of PEO solution.