Increasing Surfactant Concentration Research Articles

Removal of Emulsified Oil from Aqueous Environment by Using Polyvinylpyrrolidone-Coated Magnetic Nanoparticles

In recent years, a large amount of emulsified oily wastewaters were produced from petroleum and food industries, resulting in severe environmental problems. In this study, a series of polyvinylpyrrolidone (PVP)-coated Fe3O4 magnetic nanoparticles (MNPs) were prepared via one-step solvothermal method by introducing various amounts or types of PVP. The synthesized MNPs were characterized by multiple techniques, and their demulsification performances were evaluated in petrochemical and vegetable oil wastewaters, respectively. Results showed that the introduction of PVP in solvothermal process could significantly enhance the demulsification efficiency of MNPs, although excessive addition of PVP could not further increase its efficiency. Moreover, the effects of pH, surfactant concentration of wastewater, and the recycle number of MNPs on the demulsification performance were investigated in detail. It was found that the demulsification efficiency decreased with the increase of pH and surfactant concentration, and the synthetic MNPs were still effective after being reused for 5 cycles under acidic and neutral conditions. It is expected that the development of the PVP-coated MNPs can provide a simple and powerful route for the oily wastewater treatment.

How small can poly(N-isopropylacrylamide) nanogels be prepared by controlling the size with surfactant?

Despite the increasing demand for ‘as small as possible’ responsive poly(N-isopropylacrylamide) (pNIPAm) nanogels with well-defined internal structure, up to date there is no systematic investigation to provide guidance what are the lower limits of nanogel size and what interactions limit its further decrease. In this work both classical batch precipitation polymerization (at 60, 70 and 80 °C) and monomer-feeding precipitation polymerization (at 80 °C) is used to determine how small pNIPAm particles could be prepared by surfactant addition. The collapsed particle size levels off with increasing surfactant concentration in each case but at a strongly temperature dependent value. The plateau values of the microgel size show non-monotonic temperature dependence. To gain deeper insight into the interactions controlling the variation of microgel size with surfactant concentration and temperature a simple model was developed and fitted to the experimental data. The model fitting clearly showed that microgel size is controlled by two key parameters: the underlying adsorption isotherm of surfactant adsorption on the collapsed microgel particles and the effective initiator concentration (the amount of initiator fragments providing surface charge for the precursor particles in unit volume of reaction mixture). The significance of the formation of carboxylic groups in the polymer network is also discussed.

A structural study of a polymer-surfactant system in dilute and entangled regime: Effect of high concentrations of surfactant and polymer molecular weight

In the polymer-surfactant system, increasing the concentration of surfactant leads to structural changes in surfactant micelles. This is expected to influence the polymer conformation in the dilute regime where polymer chains are singles and in the entangled regime where the polymer system is described by the blob concept. In this report, the effect of large Sodium bis(2-ethylhexyl) sulfosuccinate (AOT), surfactant concentrations on the conformation of two polyvinylpyrrolidone (PVP) molecular weight (Mw = 55000 g/mol and Mw = 360000 g/mol) was discussed. In the first part, in the dilute regime, CPVP≺C∗where polymer chains are considered isolated, the determination of PVP (Mw = 55000 g/mol and Mw = 360000 g/mol) intrinsic viscosity [η] showed a coil to globule transition with the increase of temperature. Electrical conductivity measurements have shown the morphological transition (sphere-cylinder) of surfactant micelles with the increase of surfactant concentrations. The addition of AOT wormlike micelles revealed the expansion of PVP chains for the two molecular weight. In the second part, in PVP entangled regime,CPVP≃16C∗ where overlapped polymer chains form molecular blobs, the addition of AOT wormlike micelles to PVP solutions doesn't affect the Newtonian behavior of PVP (Mw = 55000) and the pseudo-plastic behavior of PVP (Mw = 360000 g/mol). However, AOT surfactant reinforces significantly the dynamic viscosity of PVP,η for the two molecular weight. By fitting the PVP viscosity-temperature dependence with Fulcher-Tammann-Vogel law, the results showed that the more the surfactant is added, the stronger the PVP solution becomes, which proves that AOT cylindrical (wormlike) micelles presence enhances the solid character of PVP solutions.

Formulation induces direct DNA UVA photooxidation. Part I. Role of the formulating cationic surfactant

Cetyltriethylammonium bromide (CTEAB) was considered as a cationic surfactant to form lipoplexes with DNA. In TRIS/HCl buffer, CTEAB self-assembles above its critical micelle concentration (CMC = 0.15 mM) into small spherical micelles as determined by complementary scattering techniques. This surfactant readily interacts with the supercoiled plasmid DNA pBR322 via electrostatics and hydrophobic interactions. Upon increasing surfactant concentration, successive phase transitions are observed from partial neutralization to full compaction of DNA as evidenced by agarose gel electrophoresis, tensiometry, pyrene fluorescence, UV–Vis absorbance and circular dichroism measurements. Under UVA radiation (λ ≥ 335 nm), we show that the presence of the surfactant increases photooxidized damage on DNA especially in the compacted state. A mechanistic study using selective scavengers shows the involvement of singlet oxygen in these oxidative processes due to the direct UVA absorption of DNA itself.

A mesoscopic DPD simulation study on long chain quaternary ammonium gemini surfactant solution

Dissipative particle dynamics (DPD) simulation method is applied to study the aggregation process of quaternary ammonium gemini surfactants in three systems including pure water, water-ethanol and water-oil mixture solution. The results show that DPD simulation can directly observe the formation and evolution of spherical surfactant clusters. In pure water system, higher surfactant concentration leads to form large spherical cluster. In water-ethanol system, additional ethanol molecules can destroy the stable structure of the hydrophobic radical and inhibit the aggregation of surfactant. In water-oil mixture, we find that gemini surfactants distribute in the oil-water interface, and the interfacial tension reduces as surfactant concentration increases. We studied the effect of temperature on critical micelle concentration (CMC) as well as the distribution of surfactants micelle at water-oil interface.

Effect of Ion Pairs on Nonlinear Optical Properties of Crystal Violet: Surfactants, Nano-droplets, and In Vitro Culture Conditions

Crystal violet (CV) has nonlinear optical (NLO) properties that make it suitable for photodynamic therapy. In this respect, Z-scan technique is applied to find the influence of surfactants and nano-droplets on NLO properties of CV. Nonlinear absorption coefficient and nonlinear refractive index can be further determined. The NLO parameters are also enhanced by the increase in anionic surfactant concentrations, while they remain constant with the rise in cationic ones. Moreover, the NLO parameters are extremely improved in dye-doped water droplets prepared with anionic surfactant and a continuous phase of low-polarity oils. It has been demonstrated that the interaction of ion pairs can change linear optical and NLO properties of CV that in turn can change the charge density distribution. To study the behavior of dye during in vitro culture conditions, the effect of cell culture media and fetal bovine serum on NLO properties of CV was examined.

Supramolecular gels of cholesterol-modified gellan gum with disc-like and worm-like micelles

The association between a hydrophobically modified polysaccharide, gellan gum, with micelles based on a surfactant bearing the same hydrophobic tail as pendant groups was investigated by rheology and small-angle neutron scattering (SANS). Gellan gum grafted with cholesterol groups (20% mol/mol tetrasaccharide unit), GeCh, was mixed with polyoxyethylene cholesteryl ether (ChEO10), which comprises a cholesterol group as the tail linked to a small polyoxyethylene headgroup, and self-assembles into micelles with an unusual disc-like morphology. The addition of 0.5% polymer to solutions of ChEO10 induced a remarkable transition from a Newtonian fluid to a predominantly solid-like viscoelastic behaviour, leading to a ×105 increase in zero-shear viscosity (with 5% ChEO10). Increasing surfactant concentration led to an enhancement of the viscoelasticity, but the elastic modulus G′ reached a plateau around 15% surfactant, attributed to a saturation of the sticker groups. The effect of micellar morphology on the network was studied by adding a small headgroup co-surfactant, triethylene glycol monododecyl ether, to ChEO10 micelles, which drives their elongation into wormlike micelles. Networks obtained with the long, flexible micelles displayed enhanced solid-like behaviour, with no cross-over between G′ and G″ over the measured range of frequencies, reflecting relaxation times of the order of minutes or hours. The morphology of the gels studied by SANS revealed a scattering dominated by strongly interacting micelles (described by discs of 140 Å diameter and a hydrated ∼38 Å PEO corona) and the presence of micellar clusters induced by the presence of the polymer. The scattering data therefore confirm that the onset of gelation is due to surfactant micelles acting as junction points for the network.

Kinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic CTAB surfactant

AbstractKinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic cetyltrimethylammonium bromide (CTAB) surfactant have been executed in CH3COOH‐CH3COONa buffers of pH 5.0. Spectrophotometric as well as conductometric techniques were employed to carry out the study at experimental temperature. The values of rate constant (kobs in aqueous and kψ in CTAB surfactant) and binding parameters (KB for [Zn (II)‐Trp]+ and KN for ninhydrin) have been determined by the means of a computer program referred to as linear least squares technique. Fractional‐ and first‐order kinetics were found in ninhydrin and [Zn (II)‐Trp]+, respectively, in aqueous and cationic CTAB. Study was catalyzed and accelerated by CTAB surfactant. An increase in CTAB surfactant concentration from 0 to 45 mmol kg−1 resulted to an increase in kψ from 2.5 × 10−5 s−1 to 22.7 × 10−5 s−1. Surfactant concentration beyond 45 mmol kg−1 had a slow decreasing effect in kψ. In order to elucidate CTAB effect on kψ, a pseudo‐phase model of micelles was applied.

Modeling and optimization of the niosome nanovesicles using response surface methodology for delivery of insulin

Niosome is a drug carrier with high stability and biocompatibility that provides higher drug availability, which results in improved therapeutic performance. Despite some promises that show the potential of using niosome for oral delivery of insulin, the effect of multiple factors such as the concentration of the ingredients, mechanical forces, and experimental conditions on final products make the synthesis of insulin-loaded niosomal particle with the proper characteristics very challenging. In this study, the effects of different factors including the concentration of cholesterol and surfactant, as well as duration of sonication, on zeta-potential, polydispersity index (PDI), and entrapment efficiency (EE%) of the insulin-loaded niosomal vesicles were evaluated and optimum condition was assessed in terms of cytocompatibility and in vitro drug release. The results show that the cholesterol concentration and sonication time have a significant influence on the zeta-potential, whereas the surfactant concentration plays no role. In addition, PDI increased with an increase in cholesterol and surfactant concentration but decreased with increase in the duration of sonication. Furthermore, increasing cholesterol concentration increased EE and increasing the duration of sonication decreased EE. Considering the effect of different factors, the optimum condition, which is defined as minimum PDI, maximum EE, and zeta potential >±30 mV, occurred while the concentration of the cholesterol and surfactant was 1 M and sonication time was 10 min. The zeta potential, PDI, and EE of the optimum insulin-loaded niosomal vesicles were 36.23 ± 1.04 mV, 0.53 ± 0.07 and 79 ± 2%, which were very close to the predicted values, with the prediction error below 5%. Finally, the optimum insulin-loaded niosomal vesicles were characterized in different aspects. They displayed a spherical morphology with a low tendency to be aggregated. In addition, they showed good biocompatibility with Caco-2 cells and slow release in simulated intestinal fluid.

Effect of surface charge screening on critical magnetic fields during field induced structural transitions in magnetic fluids

The field induced anisotropic structure formation in magnetic fluids (popularly known as ferrofluids) is exploited in several applications such as optoelectronic devices, sensors, heat transfer, and biomedicine. We study the role of surface charge screening on critical magnetic fields associated with field induced structural formation in a charged magnetic nanofluid of hydrodynamic diameter ∼200 nm, containing superparamagnetic iron-oxide nanoparticles of diameter ∼10 nm. Three distinct critical magnetic fields are identified from the drastic changes in transmitted forward scattering light intensity. The first critical field occurs at the commencement of small aggregate formation, the second one on completion of linear aggregation process before the commencement of lateral coalescence of individual chains, and the third one occurs when the densely packed columnar solidlike structures are formed through zippering of individual chains. During the structural transitions, the transmitted light spot is transformed into a diffused ring, with distinct speckle characteristics, due to scattering from self-assembled linear aggregates. The speckle pattern was fully reversible, and the aggregation rate was found to increase linearly with increasing surfactant concentration. The experimentally observed critical fields were in good agreement with theoretical predictions at lower surfactant concentrations. These results provide better insights into the field induced structure formation useful in designing magnetic fluidic based optical devices such as tunable filters and optical switches.

Strong competition between adsorption and aggregation of surfactant in nanoscale systems

HypothesisThe size-dependent behavior including surface tension, surface density (Γ), and critical micelle concentration (CMC) of a nanoscale liquid film containing surfactant has not been investigated until now. ExperimentsStrong competition between surface adsorption and bulk aggregation of surfactant in nanoscale systems was explored by Many-body Dissipative Particle Dynamics simulations. FindingsIn nanoscale systems, as the surfactant concentration increases, Γ continues rising even after CMC is exceeded. The saturation level of Γ is achieved only when the surfactant bulk concentration is over ten times of CMC. Moreover, both surface micelles formed by adsorbed surfactant and the sublayer below the adsorbed layer are clearly identified. The former can reduce the contacts of adsorbed surfactant with water, while the latter has the surfactant concentration significantly higher than that in bulk. The strong coupling between adsorption and micellization is attributed to large surface-to-volume ratio compared to macroscopic systems, and can be simply realized by the fact that the ratio of the numbers of surfactant distributed in bulk (nbulk) and at interface (nads) is always less than unity (nbulk/nads < 1) in nanoscale systems.

Effect of different concentrations of surfactant on the wettability of coal by molecular dynamics simulation

Anionic surfactant sodium dodecyl benzene sulfonate (SDBS) at varying concentrations was selected to investigate the influence on the wettability of Zhaozhuang Coal by molecular dynamics simulation. Six groups of water/surfactant/coal systems with different concentrations were constructed. The influence of surfactant with different concentrations on the wettability of coal was concluded by analyzing various properties from the energetic behaviors to the dynamic characteristics. The results show that the interfacial tension decreases sharply and then rises slowly with the increase of SDBS surfactant concentration, obtaining that surfactants can obviously reduce the interfacial tension. The surfactant molecules could be detected at the water/coal interface through analyzing the system’s relative concentration distribution. In addition, the difference in the wettability of surfactants on coal surfaces is caused by the spatial distribution differences of alkyl chains and the benzene ring of the surfactant molecules. And the negative interaction energy between SDBS and the coal surface indicates that adsorption process is spontaneous. Furthermore, it is of great practical significance for improving the dust reduction effect and reducing the disaster of coal dust by exploring the effects of surfactant molecules on the wettability of coal.

Structure of polyvinylpyrrolidone aqueous solution in semi-dilute regime: Roles of polymer-surfactant complexation

The effect of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) addition on the structure of polyvinylpyrrolidone (PVP) aqueous solution, in dilute and semi-dilute regimes, has been investigated at 25 °C. The intrinsic viscosity, Huggins constant, Flory exponent and the Mark-Houwink-Sakurada coefficient were deduced by viscosimetry. The structure of PVP (MW = 40.000 g/mol) aqueous solution in semi-dilute regime was described according the blob model. The monomer size, the density of monomer, the correlation length and the number of monomer in each blob were determined. The PVP-AOT interaction in water was studied in dilute and semi-dilute concentration regime of the polymer by electrical conductivity. A complexation occurs between polymer and surfactant independently on the concentration regime, where the complex nature depends on surfactant concentration. The overlapping concentration of PVP-AOT aqueous solution increases with increasing AOT concentration from 0 to 0.6 g/dl. The Flory exponent decreases from 0.545 to 0.509 and the Mark-Houwink-Sakurada coefficient decreases from 0.636 to 0.528 g/dl. The effect of AOT complexation with PVP in water was also discussed according the blob model. At the overlapping concentration, the density of monomers and the correlation length decrease with increasing surfactant concentration. The density of monomers increases from its value at the overlapping concentration as the polymer concentration increases at the semi-dilute regime. However, the monomer size, the correlation length and the number of monomer in each blob decrease from their values at the overlapping concentration as the polymer concentration increases.

Electro-rheological investigation on W/O emulsions morphology under electric fields

Five w/o model emulsions were produced using mineral oil, deionized water and Span 80. The samples of higher stability and smaller mean droplet size were produced by increasing surfactant concentration. Critical electric field stability tests were conducted, both using electrocoalescence and electrorheology, to confirm that critical field increases with decreasing droplet size. As direct current field increases, measurements of G'/G" have shown an intersection between these moduli, from which emulsions presented a predominantly elastic behavior. Optical microscopy tests suggested that such crossing point is related to a minimum electric field in which an emulsion effectively undergoes structural changes due to droplets alignment. This minimum alignment field seems to be correlated with the critical electric field once it is approximately half of critical electric field value.

Physicochemical and conformational studies on interaction of myoglobin with an amino-acid based anionic surfactant, sodium N-dodecanoyl sarcosinate (SDDS)

Physicochemical and conformational studies on the interaction between horse myoglobin, a monomeric water soluble heme protein and sodium N-dodecanoyl sarcosinate (SDDS), an amino-acid based anionic surfactant have been performed at different pHs using surface tension, viscosity, UV–vis and fluorescence spectroscopy, circular dichroism, isothermal titration calorimetry and differential scanning calorimetry. Myoglobin shows surface activity, according to the surface tension measurement. Protein forms aggregates with surfactant molecules and becomes unfolded with increasing SDDS concentration. Again, when concentration of myoglobin increases, the binding ratio decreases; whereas heme changes its spin and coordination number with increasing surfactant concentration. α-Helicity of myoglobin decreases with increase in concentration of surfactant, while β-sheet and random coil appear. The temperature of transition of myoglobin and the enthalpy of thermal denaturation also change at higher concentration of SDDS. The myoglobin-SDDS interaction at different pH, ranging from 5 to 8 has been studied and it shows that pH has very little effect on the conformational change of the myoglobin-SDDS system.

Phase diagram and surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide in a binary surfactant-water system

Phase diagram provides valuable information to describe the phase and aggregation behavior of surfactants. In this study, surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide (BDHAB) surfactant in water and their phase formations have been explored. The formation of lyotropic liquid crystalline (LLC) phases in the binary surfactant–water system was analyzed by polarized light microscopy (PLM). A comprehensive phase diagram was established presenting the existence of LLC phases as a function of surfactant concentration and temperature. The observed PLM images reveal that the BDHAB–H2O system exhibits isotropic (L1), hexagonal liquid crystalline (H1), cubic (V1), and lamellar (L∞) phases in a sequential pattern with the increase of surfactant concentration. The recorded LLC phases for bi-tail BDHAB–H2O system have also been compared with the phase diagram of single tail cetyl trimethyl ammonium bromide (CTAB)–H2O system. The present study evidence that the surfactant morphology (i.e., alkyl chain length and surfactant head-group area) has a significant influence on the formation of micellar aggregates. In addition, surface tension measurements were also performed to observe the surface adsorption behavior of BDHAB surfactant. This study will be beneficial in understanding the micelle formation and solubilization behavior of bi-tailed quaternary ammonium cationic surfactants to optimize its colloidal formulations.

Effect of Charge and Dielectric Constant on Linear and Nonlinear Optical Properties of Two Dyes

The enhancement of nonlinear optical properties of dye with surfactant can be applied in photodynamic therapy and medicine. The nonlinear optical properties of alizarin red S and rhodamine B mixed with cationic and anionic surfactant are studied by Z-scan technique. The nonlinear absorption coefficient values of cationic dye (rhodamine B) in aqueous solution are reduced with the increase of anionic surfactant concentration, while the nonlinear absorption coefficient values are enhanced by the interaction between anionic dye (alizarin red S) with anionic surfactant. The nonlinear refractive index (n2) of cationic and anionic dye is reduced with an increase of surfactant concentration. The nonlinear absorption coefficient values of a rhodamine B-doped droplet is reduced by the increase of cationic surfactant in the water droplet. In general, the nonlinear absorption coefficient values are reduced with an increase of dye solubility, and the value of n2 is reduced with an increase of dye solubility in solution. The fluorescence intensity is higher when dye and surfactant have the same charge. This effect can be due to the increase of solubility of cationic (anionic) dye with an increase of anionic (cationic) surfactant in the solution. The reduction of nonlinear absorption coefficient values with an increase of droplet size can be due to the change of rhodamine B solubility in microemulsion.

Nitrate removal from drinking water by PAN ultrafiltration assisted with cationic surfactants: evaluation of effective factors using response surface methodology

Polyacrylonitrile ultrafiltration membrane was used to remove nitrate from aqueous solution, assisted by variations in cationic surfactant type and structure [cetylpyridinium chloride (CPC) and hexadecyl trimethylammonium bromide (HTAB)]. This paper also studied the effects of membrane thickness (150, 200, 250 µm), nitrate concentration (40, 120, 200 ppm), and surfactant concentration (0.4, 5.2, 10 mM) on removal efficiency. To this end, the required experiments were designed through response surface methodology using design-expert 7.0.0 software. The results showed that CPC was generally more efficient than HTAB due to its hydrophilic head structure. Rejection was improved significantly by increasing surfactant concentration over critical micelle concentration (CMC), but a slight fall was observed for CPC at about 10 mM concentration of surfactant in all nitrate concentrations. The optimal condition was obtained at 8.18 mM CPC, 196.2 ppm nitrate and thickness of 160 µm, which resulted in rejection of 80.29% at 30th min of filtration with an average flux of 19.25 L/m2 h. Increasing pressure showed a positive effect on rejection. Also, modified PVP-optimal membranes (160 µm) associated with different polyvinyl pyrrolidone (PVP) percentages by weight showed higher flux compared to an unmodified optimal membrane. Porosity and water content of optimal membrane were 49.9% and 82.56%, respectively, and surfactants rejection was always close to 100% over CMC.

Adsorption and aggregation properties of alkoxy-group-modified homogeneous polyoxyethylene alkyl ether nonionic surfactants

The development of new surfactants with interesting properties and new functionalities that can be controlled in a simple manner is an important industrial objective. Herein, we report the synthesis of homogeneous polyoxyethylene (EO) alkyl ether nonionic surfactants modified with alkoxy groups (C12EO8OR, where C12 and EO8 are dodecyl and octaoxyethylene chains, respectively, and R = Me and Et) from a homogeneous EO-type hexaoxyethylene dodecyl ether (C12EO6) and diethylene glycol monomethyl ether or diethylene glycol monoethyl ether. The adsorption and aggregation properties of these surfactants were characterized through cloud point and surface tension measurements, and by small-angle X-ray scattering, polarization microscopy, and cryogenic transmission electron microscopy; these properties were compared to those of previously reported homogeneous EO-type (C12EO8) and polyoxypropylene-polyoxyethylene type surfactants (C12EO8POy, y = 1, 2, 3). The introduction of a methoxy or ethoxy group at the terminus of the EO chain in C12EO8 resulted in an increase in hydrophobicity and a greatly reduced cloud point. Substitution of the terminal hydroxy group of the EO chain in C12EO8 with methoxy and then ethoxy led to increasingly lower surface tensions in solution and more efficient air/water interfacial adsorption. C12EO8OR formed small micelles at low concentrations in solution, and the micelles of C12EO8OMe transformed to hexagonal liquid crystals with increasing surfactant concentration, whereas C12EO8OEt remained to form micelles even at high concentration; that is, the introduction of bulkier functional groups into the C12EO8 surfactant helps to control the formation of aggregates with higher-order structures.

Effect of number of oxypropylene on dynamic interfacial tensions of extended surfactants

Effect of the numbers of oxypropylene on dynamic interfacial tensions (IFT) of five extended surfactants C12-14PmE2S (m = 0, 3, 5, 8 and 12) were investigated. The effects of electrolyte (NaCl and CaCl2) concentration, salinity, surfactant concentration were studied in detail. The IFTs between C12-14PmE2S aqueous solutions and n-decane obtained ultralow range at optimum NaCl concentration expect C12-14E2S. The optimum salinity (S*) decreased with increase of number of oxypropylene. Also, the IFTs of C12-14P8E2S and C12-14P12E2S approached or obtained ultralow IFT in a wide range of CaCl2 concentrations. The IFTs between C12-14P12E2S aqueous solution and n-decane decreased as salinity increased. With increasing surfactant concentration, the values of IFT decreased initially and then increased.