Solutions Of Cationic Surfactants Research Articles

Direct Measurement of Lateral Correlations under Controlled Nanoconfinement.

Lateral correlations along hydrophobic surfaces whose separation can be varied continuously are measured by x-ray scattering using a modified surface force apparatus coupled with synchrotron radiation, named SFAX. A weak isotropic diffuse scattering along the equatorial plane is revealed for mica surfaces rendered hydrophobic and charge neutral by immersion in cationic surfactant solutions at low concentrations. The peak corresponds to a lateral surface correlation length ξ≈12 nm, without long-range order. These findings are compatible with the atomic force microscopy imaging of a single surface, where adsorbed surfactant stripes appear surrounded by bare mica zones. Remarkably, the scattering patterns remain stable for gap widths D larger than the lateral period but change in intensity and shape (to a lesser extent) as soon as D<ξ. This evolution codes for a redistribution of counterions (counterion release from antagonistic patches) and the associated new x-ray labeling of the patterns. The redistribution of counterions is also the key mechanism to the long-range electrostatic attraction between similar, overall charge-neutral walls, reported earlier.

Experimental study on drag reduction performance of mixed polymer and surfactant solutions

In this work, the mixed aqueous solutions of cationic surfactant – cetyltrimethyl ammonium chloride and non-ionic molecular polymer – polyacrylamide were tested to verify the speculation about their intensification possibilities of drag reduction performance. Sodium salicylate (NaSal) was used as the counter-ion salt. Six different combinations of mixed solution concentrations were tested at different temperatures ranging from 25°C to 50°C. Pure surfactant and polymer solutions were tested as control couples. It was found that the curves of mixed solutions could be divided into enhanced drag reduction zone, stable drag reduction zone and destroyed drag reduction zone. Surfactant molecules form micelles round polymer chains. Then the two additives form a kind of reinforced concrete structures, which were more complex and more effective in restrain vortices, leading to the intensification of drag reduction in enhanced zone and stable zone compared to pure surfactant solutions at low temperatures. The addition of polymers also increased drag reduction efficiency in destroyed zone by providing a wider range of Reynolds numbers. In addition, the results indicated that temperatures were more influential than concentrations, raising the temperature to change the structures of solution is more effective than increasing the quantity of structures.

Effects of additives on the viscoelastic responses of cationic gemini surfactant solutions.

Several additives, including inorganic (NaCl) and organic salts (derivatives of benzoate), were added into aqueous solutions of a gemini cationic surfactant, 2-hydroxypropyl-1,3-bis (myristyldimethylammonium chloride) (abbreviated as 14-3(OH)-14(2Cl)). The mixed systems were investigated using rheological measurement, cryo-TEM and 1H NMR analysis. The results showed that addition of salts induced rich aggregate morphologies in the 14-3(OH)-14(2Cl)/salt systems. The influence of an inorganic salt on the viscoelasticity of 14-3(OH)-14(2Cl) solutions is much weaker than that of organic salts. Furthermore, the ability of three organic salts in enhancing the viscoelasticity of 14-3(OH)-14(2Cl) solutions is in the order sodium m-hydroxybenzoate > sodium o-hydroxybenzoate > sodium p-hydroxybenzoate. The different roles of these organic salt isomers arise from the different types of hydrogen bonding formed between 14-3(OH)-14(2Cl) and the organic counter ions.

Surfactant solutions for enhancing solubility of new arylquinolin-2-ones

Micellar solutions and microemulsions have been used for the increase in the solubility of a series of arylquinolin-2-ones in water. Using spectrophotometry, the solubilization capacity of systems has been characterized with respect to arylquinolin-2-ones. As micelle-forming compounds nonionic amphiphiles are used, whose application is approved in medicinal and pharmacological practice, namely, Tween 80, Pluronic F127, Brij 35, and Tyloxapol. For comparison typical ionic surfactants are explored as well. It has been demonstrated that micellar solutions of Tween 80 can increase the content of test compounds in water up to 20 times, while microemulsions exhibit a higher effect. It has been found out that the solubilization process of arylquinolin-2-ones is accompanied by a remarkable change of their acid-base properties: the value рKа may increase by 4 units with the transition from the solutions of cationic surfactants to anionic.

Solvatochromic and protolytic properties of the indicators in the solidified gelatin gel medium

Fixed on the transparent triacetate cellulose substrate of the commercial film, the solidified gelatin gel was used for the immobilization of acid-base and solvatochromic betaine dyes. The results of microscopic studies showed that while immobilizing the reagents, the structure and morphology of the gel don’t change. Indicators are distributed uniformly in the gelatin layer of the film. Polarity parameters (ET (30) and ETN) of the solidified gelatin gel film medium and gelatin gel on the glass substrate, obtained in vitro have been estimated on account of the shifts of the spectral absorption bands of the immobilized in the film Reichardt’s betaine indicators. It was found that at pH far from the isoelectric point (pH 4.5), the polarity of the medium of the solidified gelatin layer of the film is in the intermediate position between the respective values of the acetone and ethanol. This polarity verges towards the polarity of such solvent media as nitromethane, pentan-2-ol, propylene carbonate. The influence of the gelatin matrix on the change, comparing with aqueous solutions, of the index values of the ionization constants of the acid-base indicators correlates in sign with effects, observed for the same indicators in micellar solutions of anionic and cationic surfactants. Films with immobilized dyes on it can be recommended for use in optical pH sensors when visual and spectrophotometric pH controlling.

Rheology of novel self-thickening cationic gemini surfactant solutions

ABSTRACTA new cationic Gemini surfactant (25-HP-25) was synthesized with eruamidopropyl dimethylamine and epichlorohydrin, and its solution is self-thickening. The rheological properties of 25-HP-25 and 3-chloro-2-hydroxypropyl eruamidopropyl dimethyl ammonium acetate (EDAA) solutions were compared. The solution of EDAA behaves as Newtonian fluid (1 s−1 < γ < 1000s−1). Whereas the 25-HP-25 micelle solution (2 wt%) exhibits higher viscosity, which is about three hundred times than that of EDAA solution at low shear rate (γ < 1 s−1). Especially, the 25-HP-25 solution shows obvious thixotropy, and with the increase of concentration, the viscoelasticity becomes better. Furthermore, the compaction of network structures has been confirmed by cryo-field emission scanning electron microscopy (cryo-FESEM) micrographs. This work is expected to enrich the research field of self-thickening surfactant.

Nanocomposite composed of charged wormlike micelles and magnetic particles

Wormlike micelles solutions of cationic surfactant were examined as surfactant concentration in the presence KCl salt. Dilute and semidilute regimes were determined. Concentration power law dependencies of the zero-shear viscosity and plateau modulus indicate on charged wormlike micelles network. SANS data prove long flexible wormlike micelles formation. Nanocomposite composed of the chains and magnetite particles was prepared. It was shown that particles addition leads to increase rheological parameters of the system which is in good agreement with suggestion that micellar chains can link to particles surface covered by surfactant to decrease number of end-caps.

Fluorescence quenching of α-tocopherol by graphene dispersed in aqueous surfactant solutions

The fluorescence of α-tocopherol in different solutions of zwitterionic (lauryl sulfobetaine, LSB), non-ionic (polyoxyethylene-23-lauryl ether, Brij L23) and cationic (hexadecyltrimethylammonium bromide, CTAB) surfactants, as well as in graphene (G) dispersions in these surfactants at different weight ratios has been comparatively investigated. A quenching phenomenon of the vitamin fluorescence in the micellar dispersions of G has been found, the effect being more pronounced for dispersions in Brij L23. This surfactant causes the highest degree of G exfoliation and is the most effective in stabilizing G dispersions. The fluorescence intensity ratio, calculated in the absence and in the presence of G, increases linearly with G concentration up to 30mgL−1 for dispersions in 5mM Brij L23 and in 5mM CTAB with and without NaCl. A more prominent fluorescence quenching effect is found at low surfactant concentrations, ascribed to a stronger interaction between α-tocopherol and G when the nanomaterial is less covered by the surfactant. Time-resolved fluorescence measurements indicate a static quenching mechanism between α-tocopherol and G. The fluorescence intensity and α-tocopherol concentration in 5mM Brij L23 aqueous solutions and in G (2.0wt%) dispersions in this surfactant follow a linear relationship, as well as the differences of the intensities measured in each case.

Enhanced Catalytic Activity of α-Chymotrypsin in Cationic Surfactant Solutions: The Component Specificity Revisited.

Enhanced catalytic activity (super activity) of enzymes in the presence of surfactants is of key importance in "micellar enzymology"; such super activity is not very trivial, it is highly system specific, and the mechanism behind the activity enhancement is not always well apprehended. We report the catalytic activity of α-chymotrypsin (CHT) on ala-ala-phe-7-amido-4-methylcoumarin (AMC) in the presence of cationic surfactants of different hydrophobic chain lengths: dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB). It is observed that in comparison to buffer the catalytic activity of CHT is enhanced 5-fold in premicellar DTAB solutions, while negligible changes are observed in CTAB and OTAB. Activity decreases considerably in the post micellar concentration, specifically for the latter two surfactants. A similar trend is also obtained in another substrate 2-napthyal acetate hydrolysis. Such surfactant specific superactivity is intriguing. The protein's secondary and tertiary structures in the presence of these surfactants are determined using circular dichroism (CD) spectroscopy and it is found that both CTAB and OTAB perturb the protein structure significantly, especially in the post micellar concentrations. DTAB, on the other hand, does not produce noticeable changes in the protein structure. The various pairwise interactions present in the system have been underlined using both steady-state and time-resolved fluorescence spectroscopy. Assuming a three-step kinetics model, we determine the free energy changes of the reaction, and the observations have been discussed in the light of the various interactions among the components.

Influence of trace cobalt(II) on surfactant fouling of PVDF ultrafiltration membrane

The influence of trace cobalt on membrane performance was investigated during ultrafiltration of surfactant-containing wastewater. The most serious membrane fouling occurred in cationic surfactant solution due to its higher affinity with membrane surface. With an increase of cobalt concentration, the flux decreased faster and membrane fouling became more serious, especially for ionic surfactant solutions. Using Hermia’s blocking models, the membrane fouling varied from standard pore blocking and intermediate pore blocking (0–1mg/L cobalt) to cake filtration (5mg/L cobalt). The presence of Co probably promotes fouling via two mechanisms: 1) By reducing the CMC so that micelles form more readily, which promotes size exclusion. The micelles were more easily adsorbed and rejected by the membrane, leading to more extensive membrane fouling and higher rejection of surfactants. 2) By regulating the electrical charge of micelles to be more positive so that the micelles are more easily adsorb onto membrane through electrostatic effect. Rejection and deposition of cobalt both increased in the presence of surfactants, especially higher in anionic surfactant solutions. In conclusion, the complexation of cobalt and surfactants strongly influenced ultrafiltration performance, which should be carefully considered in membrane treating wastewater containing surfactants and trace transition metals.

Turbid and transparent shear-induced structures in dilute cationic surfactant solutions

The advection of shear-induced structures (SISs) was visualized for cationic dilute surfactant solutions in a rectangular channel flow and an impinging wall jet. The SISs visualized here were transparent and distinguished as the macroscopic dark structures in contrast to the background light-scattering micelles. The SIS phase was separated from the solution and behaved like an elastic gel. In the rectangular channel flow, the threadlike SISs of centimeter order length appeared to be aligned in the direction of the flow, and the average thread length was increased with the Reynolds number and turbulent drag reduction. Although the origin of the threadlike SISs was not clear in the fully developed rectangular channel, the impinging flow developed in the streamwise direction and revealed the growing process of the SISs. The viscoelastic solution with equimolar counterions rolled up the wall SIS layer in the impinging flow, and built the cylindrical sheet-like SIS. In contrast, the solution with excess counterions presented the generation of a transparent gel-like SIS from a turbid wall shear layer, and produced a ring-like SIS. The shapes of the phase-separated SISs were dependent on both flow geometry and fluid viscoelasticity.

Drug induced micelle-to-vesicle transition in aqueous solutions of cationic surfactants

Solubilization of the drug diclofenac sodium (DS) in micellar aggregates of ionic liquid-based surfactants and cetyltrimethylammonium bromide at 25 °C induces changes to worm-like micelles and vesicles, with potential use in drug delivery.

The interactions between surfactants and the epicuticular wax on soybean or weed leaves: Maximal crop protection with minimal wax solubilization

Abstract Surfactants are commonly added to aqueous herbicide formulations to reduce the surface tension, facilitating their application. In the present study the interaction between the surface of freshly harvested soybean leaves and pure water, solutions of cationic (CTAB), anionic (SDS) and uncharged (ethoxylated sorbitan monolaurate 20 EO – ESM20) surfactants and a commercial herbicide formulation (CF) was investigated by means of contact angle measurements and scanning electron microscopy (SEM). The wettability and the hysteresis in the contact angle values determined for soybean leaves were the largest for the surfactant with the highest critical micelle concentration. The epicuticular wax on soybean leaves presented rosette-like clusters of platelets, as observed by SEM. After interaction with the surfactants or CF, most of the wax platelet rosettes disappeared from the surface, indicating that the epicuticular wax was dissolved by the surfactant. The wax contained long hydrocarbon and long chain esters, as qualitatively analyzed by gas-chromatography coupled with mass spectroscopy. The wax extracted from soybean leaves presented no significant biocidal activity against Micrococcus luteus, Staphylococcus aureus or Escherichia coli . Its protective role against pathogens depends solely on the tridimensional arrangement on the surface, which impairs the physical attachment of microorganisms to the surface. For comparison, the wettability and morphology of Eleusine indica , a common weed, was investigated. The weed leaves presented smooth surfaces and a much lower contact angle values. Therefore, surfactants should be added to the herbicide formulations with the compromise to protect the crop adequately and to minimize the solubilization of protective epicuticular wax layer on soybean leaves.

Effect of spacer length on the interfacial behavior of N,N′-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide gemini surfactants in the absence and presence of ZnO nanoparticles

In this paper the interfacial behavior of aqueous solutions of cationic gemini surfactants of the, N,N′-bis(dimethylalkyl)-α,ω-alkanediammoniumdibromide type (known as the 12-s-12 series), in the absence and presence of ZnO nanoparticles was studied. Equilibrium and dynamic interfacial tension between n-decane and aqueous surfactant solutions were investigated. It was concluded that the synergistic effect between surfactants and nanoparticles increases the surfactant efficiency with respect to reducing the interfacial tension. Moreover, the magnitude of the effect of ZnO nanoparticles on the interfacial tension decreases with increasing length of the spacer group in the gemini surfactant structure. Dynamic studies illustrate that the migration mechanism of gemini surfactants (regardless of the presence of ZnO) from the bulk to the interface was controlled by both diffusion and adsorption. The effect of spacer length on the contact angle and emulsion stability both with and without nanoparticles was also studied.

Monitoring the architecture of anionic κ-carrageenan/cationic glycine betaine amide surfactant assemblies by dilution: A multiscale approach

The interaction between glycine betaine-based cationic surfactant and algal polysaccharide κ-carrageenan was studied by investigating the dilution effect of the surfactant/polymer assemblies driven by electrostatic interactions. Two aqueous solutions of cationic surfactant and κ-carrageenan at two molar ratios (3.5 and 0.8) diluted with factors of 5 and 10 times, were tested by various analytical methods including a multiscale observation by Transmission Electron Microscopy (TEM) and Laser Scanning Confocal Microscopy (LSCM) to understand the solution behavior of surfactant and oppositely charged polymer at both nano- and micrometer scale. Raman spectroscopy as well as confocal Raman imaging were applied to give Supplementary information about the surfactant/polysaccharide interactions and the distribution of assemblies. These analyses confirmed the formation of singular hybrid surfactant/polymer nano-, microobjects and they revealed the influence of dilution on the nanostructures. These results give an insight of the mechanism of the dilution effect on surfactant/polymer assemblies that could be valuable in pharmaceutical formulations, food and cosmetics fields.

Anomalous flow properties of spherical micelle surfactant solutions passing through small-sized slits

The flow properties of complex fluids, such as aqueous solutions of polymers and surfactants, have been investigated in many studies, which revealed interesting and anomalous tendencies for several types of complex fluids in abrupt contraction and expansion flows, such as flows passing through small-sized orifices and slits. In the study, the jet thrust and excess pressure drop (net differential pressure) for experimentally observing their flow properties of water and aqueous solutions of several types of surfactants with spherical micelles in slit flows were measured. Different properties were observed for various surfactant solutions depending on the charge of the solute. The resultant jet thrust and excess pressure drop of cationic and non-ionic surfactant solutions were lower than the experimental values of water. For anionic surfactant solutions, the experimental results were similar to those of water. The types can be arranged as cationic > non-ionic > anionic in order of diminishing the jet thrust and excess pressure drop. Moreover, the effect of strong strain, boundary slip, contraction ratio, size effect, concentration, and interface phenomena was discussed.

Experimental study on drag reduction performance of surfactant flow in longitudinal grooved channels

Drag-reducing surfactant solution can provide a large-eddy environment for longitudinal microgrooves and may realize the complementarity between their drag-reduction mechanisms. In this work, the collaborative drag reduction performance of surfactant solution and longitudinal microgrooves was experimentally studied to verify the speculation about their complementary possibility. The mixture aqueous solution of cationic surfactant (cetyltrimethyl ammonium chloride) and counterion salt (NaSal) was tested in the smooth and two longitudinal microgroove channels respectively at the mass concentrations of 0.16–0.47mmol/L. It was found that the drag reduction performance of surfactant solution was enhanced by the longitudinal microgrooves. The drag-reduction mechanisms of microgrooves in water and surfactant solution were illustrated by the competition between the “peak effect” and the “restriction effect” of microgroove. Moreover, the “second peak effect” was proposed to explain the drag-reduction enhancement mechanisms for surfactant flow in microgroove channels. The groove with a larger size and roughness which might increase the drag in water could still enhance the drag reduction effectiveness of surfactant flow, and had a lower critical temperature and critical Reynolds number in surfactant solution, indicating a promising application in the heat transfer and drag reduction field. Moreover, the results of particle image velocimetry of smooth channel indirectly verified that the drag-reducing mechanism of microgroove was related to the turbulent vortex scale and the restriction effect on near-wall vortices.

Experimental study on removing water blocking effect (WBE) from two aspects of the pore negative pressure and surfactants

The phenomenon that gas permeability decreases because of the water retention is known as water blocking effect (WBE), especially in the later period of gas drainage, the WBE is more serious. In order to improve the coal seam gas drainage performance as required in the real coal mine, experimental study was carried out for removing the water blocking effect (WBE) through adopting the nuclear magnetic resonance (NMR) method, and this study is conducted from two aspects of the pore negative pressure and surfactants. Results show that: with the increase of pore negative pressure, the variation of the T2 cutoff value (T2c) experiences three stages: “stable I-reduction-stable II”. When the pore negative pressure in the coal seam is less than 360.9 Pa, the external water in the coal seam can plug the coal pores and block the gas flow passage thus the WBE occurs consequently; When it gets larger than 769.68 Pa, the external water in the coal seam will be separated from the coal pores, conducive to the gas flow passage. The WBE in coal pores larger than 68.9 μm is called the temporary WBE, for which the water can be extracted, while the WBE in coal pores smaller than 68.9 μm is called the permanent WBE and the water cannot be removed by the pore negative pressure, unless the characteristics of fracturing fluid is changed. Anionic and nonionic surfactant can remove the WBE, which is beneficial to gas drainage. The cationic surfactant solution can inhibit the release of WBE, preventing gas migration in the coal seam and decreasing gas drainage efficiency. This study offers theoretical guidance for removing the WBE and enhancing gas drainage performance in the coal mine.

How to select an optimal surfactant molecule to speed up the oil-detachment from solid surface: A computational simulation

Using molecular dynamics simulations, we have investigated the process of oil molecules detachment from dolomite surface in different surfactant solutions (anionic, cationic, nonionic, amphoteric). The effect of surfactant molecules on the process of oil detachment from dolomite surface is extensively examined. We demonstrated that oil detachment time in nonionic surfactant solution is about 4 times of that in anionic surfactant solution and cationic surfactant solution, and oil detachment time in amphoteric surfactant solution is about 6 times of that in anionic surfactant solution and cationic surfactant solution for dolomite surface. Secondly, the process of oil detachment from four kinds of mineral models (silica modified with carboxy groups, calcite, dolomite, siderite) in nonionic surfactant solution is also studied in this paper. The results demonstrate that the oil detachment time from calcite surface is about 30 times of that from dolomite surface in nonionic surfactant solution. It is demonstrated that the optimal surfactant molecule can speed up the oil detachment from a solid surface. In summary, this work provides a feasible route to choose and achieve a better oil-displacing agent based on the interaction energy between the oil molecules and solid surface, which is also important for shortening oil detachment time and contributes to its applications in cleaning fields.

Urea-based gemini surfactants: Synthesis, aggregation behaviour and biological activity

Abstract Synthesis, aggregation properties in aqueous solution and antimicrobial activity of novel urea-based cationic gemini surfactants N , N ′-bis{2-[(undecylcarbamoyl)amino]ethyl}- N , N , N′ , N ′-tetramethylalkane-α,ω-diammoniumdibromides of variable spacer length are presented as a function of surfactant molecular structure. Utilizing the experimental methods of tensiometry, dynamic light scattering, time-resolved fluorescence quenching, neutron scattering, and zeta potential, the obtained data indicate a stronger aggregation tendency of urea-based surfactants with a short spacer composed of 2 CH 2 groups which was confirmed by all applied experimental methods. As results from the comparison with the gemini surfactants without urea groups in the alkyl tails and polymethylene spacer, the presence of urea groups enhances the aggregation properties of gemini molecules through additional hydrogen bonding interactions. A simple molecular model of the hydrogen bonding interaction between neighbouring urea-based gemini molecules is provided. For longer spacers of 4–10 CH 2 groups, the existence of monodisperse spherical micelles has been confirmed. The dependence of antimicrobial activity vs. spacer length shows nonlinear parabolic behaviour with the maximum antimicrobial activity found at the spacer length of 6 CH 2 groups for bacteria and 8 CH 2 groups for fungi. This is related to a different composition of cell membrane of the used microorganisms.