Function Of Surfactant Concentration Research Articles

Thermodynamic investigation of the systems poly(ethylene glycol) + sodium pentane-1-sulfonate + water and poly(vinyl pyrrolidone) + sodium pentane-1-sulfonate + water

Thermodynamic properties for aqueous solutions containing sodium pentane-1-sulfonate (C 5SO 3Na) in the absence and presence of poly(ethyleneglycol) (PEG) or poly(vinylpyrrolidone) (PVP) determined as a function of surfactant concentration from the density, sound velocity, viscosity, conductivity and vapor–liquid equilibria data, are reported here. Densities and sound velocities, allowing for the determination of apparent molar volumes and compressibilities, were measured at 288.15–313.15 K. Changes in the apparent molar properties upon micellization were derived using a pseudo-phase-transition approach and the infinite dilution apparent molar volumes and compressibilities of the monomer and micellar state of C 5SO 3Na in the investigated solutions were determined. The values of the infinite dilution apparent molar properties of micellar states of C 5SO 3Na in aqueous polymer solutions are larger than those in pure water. Vapor–liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method at 298.15 K. The variations of the critical micelle concentration (CMC) of C 5SO 3Na in water and in aqueous PEG and PVP solutions with temperature were obtained and a comparison between the CMC of C 5SO 3Na obtained from different thermodynamic properties was also made.

Surfactant mediated phase transformation of CdS nanoparticles

In this paper, we report an observation of phase transition of CdS nanoparticles as a function of surfactant concentration. We used different concentrations of a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) to monitor phase change in CdS nanoparticles. The effect of surfactant on phase transition was investigated by several characterization techniques. To investigate the structural properties we employed X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman techniques. XRD spectrum exhibited the phase transition from hexagonal to mixed cubical phase with increasing surfactant concentration. This was also accompanied by a reduction in particle size. Raman spectra indicated blue shift in fundamental optical phonon mode (1LO) as well as increase in full width at half maxima (FWHM) corresponding to 1LO with decreasing particle size. Intensity ratio of 2LO mode of phonon to the 1LO phonon mode ( I 2LO/ I 1LO) was also found to be sensitive to particle size. UV–visible (UV–vis) absorption spectra showed the blue shift in absorption edge with increasing surfactant concentration. Photoluminescence (PL) spectra were recorded to investigate the presence of interstitial sulphur ( I S) as well as interstitial cadmium ( I Cd) in our samples.

Modulated photophysics of 2-anthracene sulphonate in micellar assembly

The association of a non-ionic surfactant of polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether (Triton X) series with 2-AS in aqueous solution has been studied by means of steady-state, time-resolved fluorescence and fluorescence anisotropy techniques. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. The association constant of the probe molecule with the non-ionic micelles of Triton X (TX), location of the probe in the micellar environment, have been determined from the change in emission characteristics of the probe as a function of surfactant concentration. The rate constant of quenching and mode of quenching of probe in micellar media have been ascertained. Quantitative estimates of the micropolarity at the binding sites of the probe molecule have been determined. Some of the environment-dependent relevant fluorescence parameters, fluorescence anisotropy ( r), have been monitored for exploring the imposed motional restriction of the microenvironment around the probe. An attempt has been made to correlate the steady-state results with time resolved study.

Tetrakis(dimethylamino)ethylene Chemiluminescence (TDE CL) Characterization of the CMC and the Viscosity of Reversed Microemulsions

A new technique for the characterization of reversed microemulsions based on tetrakis(dimethylamino)ethylene (TDE) chemiluminescence (CL) has been explored. This method is based on the transport of quenching species from the continuous nonpolar phase to the interior of micelles. The emission intensity of TDE chemiluminescence was measured as a function of time for different concentrations of surfactant. These data were fit as an exponential decay, and the decay constant, k, was found. When k was plotted as a function of surfactant concentration, there was a clear change in the trend with surfactant concentration at a certain concentration; the concentration where this change occurred was concluded to be the critical micelle concentration (CMC). Using this method, the CMC of doctyl sulfosuccinate sodium salt (AOT) was evaluated in short-chain alkanes (including n-dodecane, n-decane, n-octane, n-heptane, and isooctane), cyclohexane, and mineral oil (light), while the CMCs of sodium dodecylbenzenesulfonate (NaDDBs) and Triton X-100 (X-100) were detected in cyclohexane. The CMC values were found to range from 0.61 to 2.10 mM, and they decreased with the carbon chain length of the alkane solvent. In addition, it was found that the emission intensity of TDE chemiluminescence is sensitive to variations in solvent viscosity. TDE CL is suggested as a fluorescent molecular rotor for measuring the viscosity of the system which is nanosized.

Interaction of Azo Dye with Cationic Surfactant Under Different pH Conditions

AbstractThe aggregation induced by Alizarin Yellow R (AYR) in the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was investigated by measuring their UV–visible absorption spectra. Conductance measurements as a function of surfactant concentration below and above the critical micelle concentration (CMC) were studied. CTAB aggregation takes place at the concentration far below its normal CMC in the presence of AYR. Both hydrophobic and electrostatic interactions affect the aggregation process in aqueous solution. The dye effect on the CMC of CTAB was noted by a specific conductivity method as well. AYR–CTAB binding constant (Ks) and water–micelle partition co‐efficient (Kx) were quantified with the help of mathematical models employed to determine the partitioning of organic additives in the micellar phase. The number of dye molecules per micelle was estimated at particular CTAB concentrations above CMC, during this study.

Variations in mechanical and thermal properties of mesoporous alumina thin films due to porosity and ordered pore structure

Ordered mesoporous aluminum oxide films with porosity ranging between 5% and 37% were synthesized by evaporation-induced self-assembly (EISA) using surfactant templating. To investigate the effects of mesoporous structure on thermal properties, changes in pore structure including pore size, pore distribution, and porosity were monitored as a function of surfactant concentration (Pluronic P-123, poly(ethylene oxide) 20–poly(propylene oxide) 70–poly(ethylene oxide) 20). The ordered mesoporous alumina films were then examined to determine how their morphology influences their thermal properties. These alumina films had a body-centered cubic pore structure or a random-oriented pore structure, depending on the surfactant concentration used, and superior thermal properties were obtained by controlling porosity and pore structure. Therefore, the ordered mesoporous alumina films synthesized in this study can be used as high-temperature thermo-isolating materials.

Conductometric studies of micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) in water and water–organic solvent mixed media

The micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) has been investigated in water and water–organic solvent mixed media (organic solvents used: 1,4-dioxane (DO), dimethylformamide (DMF), ethylene glycol (EG)). The conductivity in water and in mixed media (water + organic solvent) as a function of surfactant concentration was measured at different temperatures and the data were used to find critical micelle concentration (cmc) and degree of counterion dissociation ( α) of the micelle. From the study, it is observed that the micellization tendency of the surfactant decreases in the presence of organic solvents and the increase in the cmc values is comparatively less below 20% (v/v) of organic solvents showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values. The standard free energy of micellization was found to be negative in all the cases that became less negative with the increase in the cosolvent content.

Behavior of Asphaltene Model Compounds at W/O Interfaces

Asphaltenes, present in significant amounts in heavy crude oil, contains subfractions capable of stabilizing water-in-oil emulsions. Still, the composition of these subfractions is not known in detail, and the actual mechanism behind emulsion stability is dependent on perceived interfacial concentrations and compositions. This study aims at utilizing polyaromatic surfactants which contains an acidic moiety as model compounds for the surface-active subfraction of asphaltenes. A modified pulse-field gradient (PFG) NMR method has been used to study droplet sizes and stability of emulsions prepared with asphaltene model compounds. The method has been compared to the standard microscopy droplet counting method. Arithmetic and volumetric mean droplet sizes as a function of surfactant concentration and water content clearly showed that the interfacial area was dependent on the available surfactant at the emulsion interface. Adsorption of the model compounds onto hydrophilic silica has been investigated by UV depletion, and minor differences in the chemical structure of the model compounds caused significant differences in the affinity toward this highly polar surface. The cross-sectional areas obtained have been compared to areas from the surface-to-volume ratio found by NMR and gave similar results for one of the two model compounds. The mean molecular area for this compound suggested a tilted geometry of the aromatic core with respect to the interface, which has also been proposed for real asphaltenic samples. The film behavior was further investigated using a liquid-liquid Langmuir trough supporting the ability to form stable interfacial films. This study supports that acidic, or strong hydrogen-bonding fractions, can promote stable water-in-oil emulsion. The use of model compounds opens up for studying emulsion behavior and demulsifier efficiency based on true interfacial concentrations rather than perceived interfaces.

Phase Transition in Salt-Free Catanionic Surfactant Mixtures Induced by Temperature

Aggregate transitions in salt-free catanionic surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/fatty acid were investigated as a function of surfactant concentration and temperature. Lauric acid (LA), myristic acid (MA), and palmitic acid (PA) were chosen for the current study. The TTAOH/LA mixture exhibited rich phase behavior at room temperature. With increasing total surfactant concentration (c(T)), a bluish vesicular (L(alphav)) phase, an isotropic micellar (L(1)) phase, and a birefringent lamellar (L(alpha)) phase were observed. Between the L(alphav) phase and the L(1) phase, a narrow L(alpha)'/L(1) two-phase region was determined. With increasing temperature, a transition from the L(alpha) phase to the L(1) phase was induced at higher c(T) whereas at lower c(T) an opposite transition from the L(1) phase to the L(alphav) phase was noticed. Thus surprisingly, we observed bilayer-to-micelle and micelle-to-bilayer transitions in the same catanionic surfactant system, both induced by the temperature increase. Replacing LA by MA and PA caused a continuous increase in the average Krafft point of the mixture. The L(alphav)-phase region and phase-separated region become larger. Moreover, a single L(1)-phase region was absent within the investigated temperature range.

Study of Micellar Behavior of Crown Ether and Tetraethylammonium Bromide in Aqueous Media

Conductivity measurements have been carried out to study the micellar behavior of tetraethylammonium bromide in presence of 15‐crown‐5 in aqueous media. The measurements were carried out at 298.15 K as a function of surfactant concentration with varying concentrations of crown ether. The influence of this association on the micellar parameters, such as the cmc (critical micellization concentration) and β (degree of counterion dissociation) have been analyzed. Thermodynamics of the systems were discussed in terms of the change in free energy of micellisation, ΔG0m by applying the charged pseudo‐phase separation model. The trend shows that the micellization becomes less spontaneous in presence of crown ether. The influence of the presence of the inclusion complex on the micellization process of the surfactant has been studied.

Aqueous Solution of Anionic Surfactants Mixed with Soils Show a Synergistic Reduction in Surface Tension

Water retention and transport in soils is dependent upon the surface tension of the aqueous phase. Surfactants present in aqueous solution reduce the surface tension of aqueous phase. In soil–water systems, this can result in water drainage and reductions in field capacity and hydraulic conductivity. In this investigation, the surface tension of surfactant solutions mixed with soil—in a constant fixed ratio—was measured as a function of surfactant concentration. Two anionic surfactants were used: sodium dodecyl sulphate and sodium bis (2-ethylhexyl) sulfosuccinate. Two soils were also used—a clay soil and a sandy soil. The key observation made by this investigation was that the addition of soil to the surfactant solution provided a further component of surface tension reduction. Neither soil sample reduced the surface tension of water when surfactant was absent from the aqueous phase, though both soils released soil organic matter at low surfactant concentrations as shown by measurement of the chemical oxygen demand of the supernatant solutions. Furthermore, both surfactants were shown to be weakly adsorbed by soil as shown by the use of a methylene blue assay. It is therefore proposed that the additional reduction in surface tension arises from synergistic interactions between the surfactants and dissolved soil organic matter.

Calculation of contact angles from surfactant adsorption isotherms

Wetting in the system hematite–water–diisobutyl ketone was studied in the presence of an anionic surfactant, hexadecyl sulfonic acid. Adsorption isotherms of surfactant on hematite powder were measured separately at the interfaces between hematite–water and hematite–ketone, and the interfacial tension of the water–ketone interface was determined as a function of surfactant concentration. The Gibbs and Young’s equations were used to calculate contact angles from the adsorption data. For comparison, contact angles were measured as a function of surfactant concentration on the face of a hematite crystal selected from the same supply of specular hematite used for preparing the hematite powder. Overall, contact angles calculated from the equations correlate closely with measured contact angles.

Aqueous foam stabilized by hydrophobically modified cellulose and alkyl polyoxyethyl sulfate complex in the presence and absence of electrolytes

The foam prepared by sodium dodecyl polyoxyethyl sulfate (AES) with hydrophobically modified cellulose (HMHEC) solution in the presence and absence of electrolytes (NaCl, CaCl 2) is evaluated by foam stability (drainage half-life) and the configuration variations of AES–HMHEC complexes at the air/water interface. The configurations of the surfactant–polymer complexes at the air/water interface as a function of surfactant concentration are speculated by the surface tension isotherm and dilatational viscoelastic behavior. It is concluded that the configuration of AES–HMHEC complexes significantly affects drainage half-life and foam decay. When the surfactant concentration is lower than the critical aggregation concentration (CAC), the surfactant molecules are dispersed in the bulk solution but they are gradually associated at the air/water interface of the foam film which contributes to retard the foam decay. With the further increase of surfactant concentration (between CAC and the saturation concentration of surfactant associated with polymer), the association of surfactants with polymers improves the foam stability and the stability of adsorbed surfactant–polymer complexes layer. When the surfactant concentration is higher than the saturated concentration, the air/water interface is mainly covered by the surfactants rather than the surfactant–polymer complexes and hence the stability of adsorbed surfactants layer decreases. In addition, the stability of adsorbed surfactant–polymer complexes layer is enhanced by the addition of electrolytes due to the screening effects. Furthermore, compared with monovalent ions (Na +), the solution containing higher valent ions (divalent Ca 2+) stabilizes the foam film more efficiently due to the higher packing density of the complex at the air/water interface.

Micelle Formation Effect on Electroacoustics in an Aqueous Surfactant Solution: Colloid Vibration Current and Ion Vibration Current

We measured the ultrasonic vibration current of aqueous solution of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) as a function of surfactant concentration at 298.15 K under atmospheric pressure. The dependence of vibration current on the surfactant concentration exhibited a break point around the critical micelle concentration (CMC) in the DTAB system, whereas no break point was observed in the DTAC system. Taking account of the theory for vibration current, this suggests that the vibration current in the concentration regime higher than CMC depends on the electrostatic properties of micelle surface. From the difference in the slope of vibration current versus molarity curve above CMC, it was found that the zeta-potential of DTAC micelle is larger than that of DTAB micelle. This can be explained by the dissociation degree of counterions from the micelle surface. In addition, the theoretical equation of vibration current enabled us to estimate the partial molar volume of surfactant ions from the different behavior of vibration current in the concentration regime lower than CMC.

Characterization and micellization of rhamnolipidic fractions and crude extracts produced by Pseudomonas aeruginosa mutant MIG-N146

Two representative rhamnolipidic fractions, RL-F1 and RL-F2, produced by the P. aeruginosa mutant strain MIG-N146, were separated and chemically characterized by TLC, HPLC-MS, and FTIR. The RL-F1 fraction is predominantly mono-rhamnolipid homologues with a high content of one or two fatty acid moieties. The RL-F2 fraction is mainly composed of di-rhamnosyl moieties with two hydrophobic tails. Micellization behavior was investigated to assess the physicochemical properties of the surfactants, RL-F1, RL-F2, and crude rhamnolipidic extracts. The variations in morphology of micelle formation and growth were examined by dynamic light scattering measurements as a function of surfactant concentration. Critical micelle concentration (CMC), average minimal surface tension ( γ CMC ), saturated surface excess ( Γ m ), mean surface area per molecule ( S), and adsorption efficiency ( pC 20) were determined from the surface tension profiles and compared for the three surfactant systems. It was found that micelle growth was significantly enhanced by increasing rhamnolipid bulk concentration, which was most probably accompanied with an aggregate shape transition. Well-separated multi- or bi-modal distributions of particle size were observed in RL-F2 and the crude extracts solutions. The results of this study demonstrate that molecular architecture of different surfactant compositions profoundly influences the performance of rhamnolipidic surfactants.

Photophysics of the phenoxazine dyes resazurin and resorufin in direct and reverse micelles

The photophysics of the phenoxazin-3-one dyes resazurin and resorufin was studied in a micellar solution of cetyltrimethylammonium chloride and in reverse micelles of 1,4-bis(2-ethylhexyl)sulfosuccinate and benzylhexadecyldimethylammonium chloride. Absorption and fluorescence emission spectra, as well as fluorescence lifetimes and T–T transient absorption spectra were determined as a function of surfactant concentration. In the presence of direct micelles of cetyltrimethylammonium chloride, both dyes displayed red shifts in the absorption and fluorescence spectra together with a simultaneous fluorescence lifetime increase. The electrostatic attraction between the anionic dyes and the positive micellar interface favors the location of the dyes closer to the head groups of the surfactant molecules. In reverse micellar systems the spectral properties depended upon the charge of the surfactant and water content. In the case of 1,4-bis(2-ethylhexyl)sulfosuccinate, at low water content both dyes were incorporated into the interface; as the water content increased their spectral properties tended to those in pure water. In contrast, in the case of cationic surfactant, the dyes were located in the interfacial pseudophase as a result of electrostatic interactions.

Stability of Microbubble-Based Drilling Fluids Under Downhole Conditions

Abstract Colloidal gas aphrons (CGA) have the unique ability to form a bridge in the pores of reservoirs, which stops fluid invasion. Sizing microbubbles in accordance with the rock pore size distribution is imperative for effective sealing during drilling. The effects of time, temperature and pressure on the stability and size of the microbubbles needs to be better understood in order to design a fluid that will sufficiently block the pores of the formation for extended periods. In this study, the effects of time, pressure and temperature on the size of microbubbles and the stability of microbubble (CGA)-based drilling fluids were investigated. The change in the CGA diameter with time was determined by using a microscopic imaging technique. Effects of base fluid viscosity and surfactant concentration on the size and stability of the microbubbles were also investigated. Introduction CGA-based drilling fluids have been successfully used in high-angle and horizontal well drilling in highly depleted reservoirs(1). Microbubbles in CGA-based drilling fluids form a bridge in front of the pores of the rock. This bridge is believed to stabilize the rock while sustaining minimal damage to the formation. Stability of the microbubbles and how bubble size changes as a function of downhole conditions (i.e. temperature and pressure) are some of the major concerns associated with the application of CGA-based drilling fluids. A stable CGA structure requires maintaining an ideal film wall thickness of 4 to 10 microns(2). Another factor affecting CGA stability is the rate of transfer of the surfactant molecules between the viscous water shell and the bulk phase due to gravity drainage or temperature gradients. This leads to a surface tension gradient at the surface of the shell. As a result, the Marangoni Effect will counteract this deformation(3–4). Increasing the viscosity of the shell can help to minimize the transfer of surfactant molecules. Usually a biopolymer is added to adjust the shell viscosity(3). The third property that the CGA structure must have is low diffusivity, which is the ability of the air that is in the core to transfer to the aqueous shell. CGA bubble size and stability have been the subject of earlier studies(5–12). Longe(6) analyzed the bubble size distribution of CGAs for soil and groundwater decontamination applications. Longe's analyses included effects of surfactant concentration, surfactant type and electrolytes on the stability of the CGAs over the time. Jauregi et al.(7) also investigated the stability of CGAs as a function of surfactant concentration. Results from both studies indicated that the stability of CGAs increase with increasing surfactant concentration. Chaphalkar et al.(8) measured the size distribution of CGAs using a particle size analyzer. The CGAs were virtually non-existent after 20 minutes for three different types of surfactant. Roy et al.(9) reported similar results. Amiri and Woodburn(10) studied the rate of drainage, as well as the CGA bubble size, by recording the images of the CGAs over time. They reported that after 10 minutes, the bubble shape had changed from spheres to polyhedral structures.

Henry’s Law Constants for Fragrance and Organic Solvent Compounds in Aqueous Industrial Surfactants

Henry’s law constants (kH) were measured (at 30 °C) and modeled for a suite of fragrance and solvent compounds in aqueous solutions of three structurally diverse industrial surfactants: sodium dodecylbenzene sulfonate (NaDBS), tetradecylbenzyldimethyl ammonium chloride (TDBAC), and a linear alkyl ethoxylate, Neodol 1,9. kH values for limonene, β-pinene, toluene, and trichloroethene were examined as a function of surfactant concentration. When compared to TCE and toluene, the fragrances limonene and β-pinene with their larger values of molecular polarizability (ὰmol = (17.94 ± 0.5) A3and (17.34 ± 0.5) A3, respectively) and greater hydrophobic character exhibited greater affinity for micelles of the linear alkyl ethoxylate relative to those of NaDBS and TDBAC and greater selectivity overall in their interaction(s) with micelles of varying carbon content (Cn). Using a linear solvation energy relationship (LSER) of the form ln kH = C + sπ2* + aΣα2 + bΣβ2 (π2* = solute dipolarity/polarizability; Σα2 = overall ...

System peaks in micellar electrophoresis: I. Utilization of system peaks for determination of critical micelle concentration

A new way to determine the critical micelle concentration (CMC) based on the mobilities of system peaks is presented. A general approach for the CMC determination is based on the change of the slope or on finding the inflection point in the plot of a physical property of solution as a function of surfactant concentration. The determination of CMC by system peaks in CE utilizes a "jump" instead of a continuous change in the measured quantity. This phenomenon was predicted by the program PeakMaster, which was modified for simulation of micellar systems. The simulation of the steep change in mobilities of the anionic system peaks showing the CMC value was verified experimentally in a set of measurements, where the concentration of the surfactant was varied while the ionic strength was kept constant. The experimental work fully proved our model. A comparative electric current measurement was carried out. The proposed method seems to offer easier CMC determination as compared to the standard methods.

Surfactant Adsorption: A Revised Physical Chemistry Lab

Many physical chemistry lab courses include an experiment in which students measure surface tension as a function of surfactant concentration. In the traditional experiment, the data are fit to the Gibbs isotherm to determine the molar area for the surfactant, and the critical micelle concentration is used to calculate the Gibbs energy of micelle formation. In the experiment described here, students fit their data to the Szyszkowski equation, allowing them to also calculate the Gibbs energy of surface adsorption. In addition, we use this experiment to introduce nonlinear custom curve fitting.