Surfactants In Mixed Micelles Research Articles

Remediation of oil-polluted soil using anionic and non-ionic composite biosurfactants

ABSTRACT Petroleum hydrocarbons as pervasive pollutants pose a significant threat to soil ecology and human health. Surfactant washing as an established technique can effectively remediate soils contaminated by hydrocarbons. Biosurfactants, which combine the properties of surfactants and environmental compatibility, have attracted increasing interest. However, due to the high production cost of biosurfactants, their practical application is restricted. This study addressed these limitations by selecting two biosurfactants, β-cyclodextrin (C1) and sodium carboxymethyl cellulose (C2), and developed a promising cleaning agent formula through compounding and the addition of suitable additives. When the volume ratio of C1 to C2 was 8:2 and an 8 g/L mixture of sodium humate and sodium carbonate electrolyte was added, the surfactant system’s surface tension reached a minimum, yielding optimal oil removal. The formation and synergistic behaviour of mixed micelles of surfactants were explained using ideal solution theory and the Rubingh model. By optimising the oil washing process parameters – normal temperature of 25 °C, pH 11, washing time of 2 h, solid–liquid ratio of 1:5, and oscillation frequency of 200 r/min – the oil removal rate achieved 76%. This cleaning agent, characterised by low production cost, straightforward application, environmental compatibility, and rapid, significant cleaning effect, shows potential for field-scale purification of petroleum-contaminated soil.

Antagonistic Toxic Effects of Surfactants Mixtures to Bacteria Pseudomonas putida and Marine Microalgae Phaeodactylum tricornutum.

Surfactants can be found in an ever-widening variety of products and applications, in which the combination of several types of surfactants is used to reinforce their properties, looking for synergistic effects between them. After use, they tend to be discarded into wastewater, ending up in aquatic bodies with concerning harmful and toxic effects. The aim of this study is the toxicological assessment of three anionic surfactants (ether carboxylic derivative, EC) and three amphoteric surfactants (amine-oxide-based, AO), individually and in binary mixtures of them (1:1 w/w), to bacteria Pseudomonas putida and marine microalgae Phaeodactylum tricornutum. Critical Micelle Concentration (CMC) was determined to demonstrate the capacity to reduce surface tension and the toxicity of the surfactants and mixtures. Zeta potential (ζ-potential) and micelle diameter (MD) were also determined to confirm the formation of mixed surfactant micelles. The Model of Toxic Units (MTUs) was used to quantify the interactions of surfactants in binary mixtures and to predict if the concentration addition or response addition principle can be assumed for each mixture. The results showed a higher sensitivity of microalgae P. tricornutum to the surfactants tested and their mixtures than bacteria P. putida. Antagonism toxic effects have been detected in the mixture of EC + AO and in one binary mixture of different AOs; this is to say, the mixtures showed lower toxicity than expected.

Rationalizing the Design of Pluronics-Surfactant Mixed Micelles through Molecular Simulations and Experiments.

Aqueous systems comprising polymers and surfactants are technologically important complex fluids with tunable features dependent on the chemical nature of each constituent, overall composition in mixed systems, and solution conditions. The phase behavior and self-assembly of amphiphilic polymers can be changed drastically in the presence of conventional ionic surfactants and need to be clearly understood. Here, the self-aggregation dynamics of a triblock copolymer (Pluronics L81, EO3PO43EO3) in the presence of three cationic surfactants (with a 12C long alkyl chain but with different structural features), viz., dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and ethanediyl-1,2-bis(dimethyldodecylammonium bromide) (12-2-12), were investigated in an aqueous solution environment. The nanoscale micellar size expressed as hydrodynamic diameter (Dh) of copolymer-surfactant mixed aggregates was evaluated using dynamic light scattering, while the presence of a varied micellar geometry of L81-cationic surfactant mixed micelles were probed using small-angle neutron scattering. The obtained findings were further validated from molecular dynamics (MD) simulations, employing a simple and transferable coarse-grained molecular model based on the MARTINI force field. L81 remained molecularly dissolved up to ∼20 °C but phase separated, forming turbid/translucent dispersion, close to its cloud point (CP) and existed as unstable vesicles. However, it exhibited interesting solution behavior expressed in terms of the blue point (BP) and the double CP in the presence of different surfactants, leading to mixed micellar systems with a triggered morphology transition from unstable vesicles to polymer-rich micelles and cationic surfactant-rich micelles. Such an amendment in the morphology of copolymer nanoaggregates in the presence of cationic surfactants has been well observed from scattering data. This is further rationalized employing the MD approach, which validated the effective interactions between Pluronics-cationic surfactant mixed micelles. Thus, our experimental results integrated with MD yield a deep insight into the nanoscale interactions controlling the micellar aggregation (Pluronics-rich micelles and surfactant-rich micelles) in the investigated mixed system.

Synthesis of bridged-organosilica nanotubes with widely adjustable inner diameter based on temperature-dependent templating by swollen mixed surfactant micelles

The mixture of Pluronic F108 (EO132PO50EO132) and P104 (EO27PO61EO27) surfactants combined with toluene (swelling agent) templates ethylene-bridged organosilica nanotubes, whose size is widely adjustable by changing the initial synthesis temperature. While nanotubes of inner diameters ∼11 nm formed at room temperature, the temperature decrease led to the size increase and afforded nanotubes of particularly large inner diameters (from 25 to ∼35–40 nm) and thick walls at 7.5–9.25 °C, with outer diameters reaching ∼80 nm. The thick walls make these nanotubes resistant to collapse and suppress the nanotube aggregation. The stirring rate during the initial stage of the synthesis was an important factor in determining the uniformity and size of the ultra-large-diameter nanotubes. Slow stirring may lead to thin-walled organosilica nanotubes with outer diameters above 80 nm, showing that such structures can form, but their content and diameter uniformity were low. Our results suggest that the tubular soft-templating system transitions from the swollen micelle regime to the microemulsion regime, in which the inner core consists of the swelling agent only. In the latter case, the inner diameter of the surfactant-templated nanotubes, which is expected to be related to the size of the hydrophobic domain, may be enlarged to 35–40 nm (for good-quality products) or even beyond 40 nm (for low-purity products). Methylene-bridged organosilica nanotubes with tunable diameters, including very large ones, were also obtained, suggesting a broader scope of our pore diameter adjustment approach. Ethenylene- and xylylene-bridged organosilica nanotubes were also synthesized, indicating a wide applicability of our templating system.

Fourier transform infrared spectroscopy in surfactant science: A personal view

AbstractThe overall goal of this review paper on Fourier transform infrared spectroscopy (FT‐IR) is to provide non‐specialists and spectroscopists alike a motivational introduction to how this technique may be used to obtain unique structural information on a wide range of surfactant‐based systems. Two main topics are addressed—The structures of surfactant aggregates in solution and the interactions of surfactants in solution with solid surfaces. Infrared spectra can yield insights into the interactions of surfactants in mixed micelles as well as in microemulsions. The structures of adsorbed surfactant layers and their kinetics of formation may be elucidated from FT‐IR spectra obtained using attenuated total reflectance sampling techniques. Insights into the detergency process of solid oily soils may also be obtained from the spectra of phases formed at the soil‐surfactant solution interface. Future work in applying FT‐IR to the development of the hydrophilic–lipophilic difference + net average curvature (HLD‐NAC) framework is proposed. Spectral interpretation principles examined in many examples, particularly regarding surfactant hydration and the loci of oil solubilization, could be used in the further development of HLD‐NAC through application to some microemulsion systems that have recently been reported.

Binding of Perfluorooctanoate to Poly(ethylene oxide)

To inform the design of polymer-based adsorbent materials for sequestration of per- and polyfluoroalkyl substances (PFAS) from aqueous solution, we report here on the critical aggregation concentration (CAC), shape, size, composition, and interactions of assemblies formed in water between perfluorooctanoic acid ammonium salt (PFOA) and the nonionic polymer poly(ethylene oxide) (PEO), obtained from complementary experiments (conductivity, surface tension, pyrene fluorescence, viscosity, and small-angle neutron scattering (SANS)) and atomistic molecular dynamics (MD) simulations. PEO–PFAS binding commences at concentrations lower than the PFOA critical micelle concentration (CMC) and is driven by PEO localizing on the micelle surface and shielding the fluorocarbon parts of PFOA from contact with water. PFOA + PEO mixed micelles have a 10% higher association number and are 40% more elongated compared to polymer-free PFOA micelles. This is the first investigation on the structure of polymer + fluorocarbon surfactant mixed micelles and contributes fundamental insights into the association of water-soluble polymers with PFAS surfactants.

Impact of wormlike micelles on nano and macroscopic structure of TEMPO-oxidized cellulose nanofibril hydrogels.

In this work, we investigated the effect of adding surfactant mixtures on the rheological properties of TEMPO-oxidized cellulose nanofibril (OCNF) saline dispersions. Three surfactant mixtures were studied: cocamidopropyl betaine (CAPB)/sodium dodecyl sulfate (SDS), which forms wormlike micelles (WLMs); cocamidopropylamine oxide (CAPOx)/SDS, which forms long rods; and CAPB/sodium lauroyl sarcosinate (SLS), which forms spherical micelles. The presence of micelles in these surfactant mixtures, independent of their morphology, leads to an increase of tan δ, making the gels less solid-like, therefore acting as a plasticizer. WLMs were able to suppress strain stiffening normally observed in OCNF gels at large strains. OCNF/WLM gels have lower G' values than OCNF gels while the other micellar morphologies have a reduced impact on G'. The presence of unconnected micelles leads to increased dissipative deformation in OCNF gels without affecting the connectivity of the fibrils, while the presence of entangled micelles interferes with the OCNF network.

Physicochemical investigations of mixed micelles of cationic gemini surfactants with different triblock polymers

The surface tensions of cationic geminis, alkanediyl-α,ω-bis(dimethylalkylammonium bromide) (mGs—m = 14,16 and s = 5,6) + triblock polymers (TBPs—F68, F127, L64) mixtures, over the entire mole fraction range were determined. Cationic conventional surfactants, alkyltrimethylammonium bromides (TTAB, CTAB) + TBP systems, were also studied for comparison. Analysis of the data by means of regular solution theory revealed that the adsorbed monolayer at the air/water interface was much richer in surfactants than the micelles and the intermicellar solution. The interaction between surfactants and TBP molecules at the air/water interface was strong in most of the cases. The participation of monomeric surfactants was lower than of gemini surfactants. The critical micelle concentration (cmc) was studied by the regular solution theory and the interaction parameter; the activity coefficient and the activity of components in mixed micelles were determined. The micelle composition at the cmc was also computed, and it was found that the mixed micelles were systematically richer in TBPs. Participation of surfactants in mixed micelles is lower than their contribution at interface.

Catalysis of radical reactions in mixed micelles of surfactants with hydroperoxides

The peculiarities of the catalytic action of cationic surfactants (CSurf) in combination with hydroperoxides on the generation of radicals and the influence of various factors on this process (transition metal compounds, oxygen, and external magnetic field) were considered. In the oxidized hydrocarbons (RH), hydroperoxides (ROOH), which are the primary amphiphilic products of oxidation, form mixed micelles {mROOH…nCSurf} with CSurf, in which fast decomposition of ROOH into radicals occurs and other polar components (metal compounds, inhibitors, etc.) can concentrate, which significantly affects the rate and mechanism of oxidation. The cationic surfactants immobilized on a solid support retain the ability to catalyze the decomposition of hydroperoxides, forming radicals, and to initiate radical oxidation and polymerization. It was found that acetylcholine, which is the most important neurotransmitter that plays an important role in the neuromuscular and cognitive activity of living beings, like cationic surfactants, catalyzes the radical decomposition of hydroperoxides in organic media, and the yield of radicals in this process decreases in a magnetic field and in the presence of oxygen.

Synergistic Interaction between Nonionic Octylphenol Polyoxyethylene Ethers and Effect of Hydrophilic Chain

AbstractThe micellization of binary mixture composed of nonionic octylphenol polyoxyethylene ether (OP‐n, n is the average number of oxyethylene unit) and its homologues, as well as the effect of hydrophilic chain were investigated. The tensiometry was adopted to determine the critical micelle concentration of binary surfactant mixture. According to the regular solution theory, some thermodynamic models were used to predict the parameters of micellization and the thermodynamic parameters. For all the three binary mixtures of nonionic/nonionic surfactants, each of which shows a nonideal mixing and can behave synergistically in aqueous solution. For both the mixture of OP‐10/OP‐7 and the mixture of OP‐10/OP‐4, the positive deviation of the mole fraction of surfactant in mixed micelle from its ideal value coexists with the negative deviation in the entire range of compositions in aqueous solution, while for the mixture of OP‐7/OP‐4, it only shows a positive deviation. Thermodynamic data indicate that for all the three binary surfactant mixtures, the process of micellization is entropically spontaneous, and the change of hydrophilic chain results in the difference in the stability of mixed micelle. The results can be explained by the steric effect, the hydrogen bonding and the hydration. The work helps with understanding the interaction between molecules and properties for some industrial products constituted by nonionic surfactant and its homologues.

Self-aggregation of ionic liquid-cationic surfactant mixed micelles in water and in diethylene glycol–water mixtures: Conductometric, tensiometric, and spectroscopic studies

Interaction of imidazolium based surface-active ionic liquid (SAIL), 1-decyl-3-methylimidazolium chloride [C10mim][Cl], with cationic surfactant cetrimide (CET) has been studied by using conductometric, tensiometric, and spectroscopic methods in pure water and in presence of diethylene glycol (DEG)–water binary mixtures. Addition of DEG has marked effect on the thermodynamic and aggregation behavior of these studied systems. From conductometric approach various parameters have been calculated such as critical micelle concentration, (cmc), micellar mole fraction, X1, of component 1 (CET), micellar interaction parameter, β, activity coefficients ƒ1 and ƒ2 of component 1 and component 2 (SAIL), standard Gibbs energy of micellization (ΔGm0), and degree of counter ion dissociation (g). Rubingh's non-ideal solution theory confirms the attractive and non-ideal behavior among the surfactant molecules in the mixed micelles. From the tensiometric studies different parameters such as surface tension reduction efficiency (pC20), maximum surface excess concentration (Γmax), minimum area per surfactant molecule (Amin) and standard Gibbs free energy of adsorption ΔGad0 at the interface were evaluated. The packing parameters of amphiphiles in the micelles, P, volume contribution of the hydrophobic chain, v, and its effective length, lC have also been evaluated for the pure and mixed systems. The micelles/mixed micelles formed have spherical geometry. Cresol red, an anionic dye, was used as a probe for UV–visible spectra of pure and mixed systems, which supports the role of SAIL in the mixed micellization process.

Inverted Micelle-in-Micelle Configuration in Cationic/Carbohydrate Surfactant Mixtures.

Nuclear magnetic resonance is applied to investigate the relative positions and interactions between cationic and non-ionic carbohydrate-based surfactants in mixed micelles with D2 O as the solvent. This is accomplished by using relaxation measurements [spin-lattice (T1 ) and spin-spin (T2 ) analysis] and nuclear Overhauser effect spectroscopy (NOESY). This study focuses on the interactions of n-octyl β-d-glucopyranoside (C8G1) and β-d-xylopyranoside (C8X1) with the cationic surfactant hexadecyltrimethylammonium bromide (C16 TAB). Whereas the interactions between carbohydrate and cationic surfactants are thermodynamically favorable, the NOESY results suggest that both of the sugar head groups are located preferentially at the interior core of the mixed micelles, so that they are not directly exposed to the bulk solution. The more hydrophilic sugar headgroups of C8G1 have more mobility than sugar heads of C8X1 owing to increased hydration. Herein, an inverted carbohydrate configuration in mixed micelles is proposed for the first time and supported by fluorescence spectroscopy experiments. This inverted carbohydrate headgroup configuration would limit the use of these mixed surfactants when access to the carbohydrate headgroup is important, but may present new opportunities where the carbohydrate-rich core of the micelles can be exploited.

Thermodynamic Study of Mixed Surfactants of Polyoxyethylenetert-Octyl Phenyl Ether and Dodecyltrimethylammonium Bromide

Mixtures of polyoxyethylene tert-octyl phenyl ether (TX100) and dodecyltrimethylammonium bromide (DTAB) were investigated using isothermal titration calorimetry. On the base of the pseudophase separation model and using the two-parameter Margules equation, the compositions of mixed micelles and activity coefficient of each surfactant in mixed micelles were obtained and further used to calculate the thermodynamic parameters of micellization and excess properties of mixed surfactants in the micelles. Through three titration methods, the tendency of surfactants to form mixed micelles and the interactions between TX100 and DTAB in the micelles were investigated.

Complexation between Sodium Poly(styrenesulfonate) and Alkyltrimethylammonium Bromides in the Presence of Dodecyl Maltoside.

In the present paper, the impact of dodecyl maltoside (C12G2) on the association of sodium poly(styrenesulfonate) (PSS) with dodecyl- and hexadecyltrimethylammonium bromides (DTAB and CTAB) was studied. A low amount of nonionic surfactant enhances the binding of the investigated cationic amphiphiles on PSS, reducing the cationic surfactant-to-polyanion ratio needed for charge neutralization and precipitation. This effect is more pronounced for DTAB than for CTAB due to the considerably higher free surfactant concentration of the former cationic amphiphile. The synergistic surfactant binding also affects the nonequilibrium features of PSS/CTAB association via enhancing the kinetically stable concentration range of overcharged polyion/surfactant nanoparticle dispersions. With increasing C12G2 concentration, however, an opposite effect of the uncharged additive dominates. Namely, the CTAB molecules are solubilized excessively into mixed surfactant micelles, which reduces the surface charge of the PSS/CTAB/C12G2 nanoparticles and thus destabilizes their dispersion. At appropriately large nonionic surfactant concentrations, the binding of CTAB is largely reduced, resulting in the redissolution of the precipitate. In contrast, neither the destabilization nor the resolubilization effects of the added dodecyl maltoside were observed for the PSS/DTAB system due to the much lower driving force of DTAB binding compared to CTAB. Our results clearly demonstrate that the alkyl chain length of the ionic amphiphile has a pronounced effect on both the equilibrium and nonequilibrium aspects of polyion/mixed surfactant complexation which might be further exploited in various next generation applications.

Binary mixtures of cationic surfactants with triton X-100 and the studies of physicochemical parameters of the mixed micelles

The mixtures of alkylpyridinium chloride (C n PC, n=14, 16) and Triton X-100 were studied over the entire mole fractions at 298.15 K. For each mixture, CMC was obtained from surface tension measurements. To estimate the interaction parameter values (β), the calculation of the monomer concentrations and the mole fractions of the individual surfactants in the mixed micelles, the CMC data were used by applying the regular solution theory. The obtained results showed that the increase of the chain length of C n PC led to the stronger preferential incorporation of cationic surfactant in mixed micelle. The large values of |ΔG o | confirmed that mixed micelle of C16PC and Triton X-100 was significantly favorable.

Impact of cationic surfactant on the self-assembly of sodium caseinate.

The impact of a cationic surfactant, dodecylammonium chloride (DDACl), on the self-assembly of sodium caseinate (SC) has been investigated by light scattering, zeta potential, and rheological measurements as well as by microscopy (transmission electron and confocal laser scanning microscopy). In SC dilute solutions concentration-dependent self-assembly proceeds through the formation of spherical associates and their aggregation into elongated structures composed of connected spheres. DDACl interacts with SC via its hydrophilic and hydrophobic groups, inducing changes in SC self-assembled structures. These changes strongly depend on the surfactant aggregation states (monomeric or micellar) as well as concentration ratio of both components, leading to the formation of soluble and insoluble complexes of nano- to microdimensions. DDACl monomers interact with SC self-assembled entities in a different way compared to their micelles. Surfactant monomers form soluble complexes (similar to surfactant mixed micelles) at lower SC concentration but insoluble gelatinous complexes at higher SC concentration. At surfactant micellar concentration soluble complexes with casein chains wrapped around surfactant micelles are formed. This study suggests that the use of proper cationic surfactant concentration will allow modification and control of structural changes of SC self-assembled entities.

Study of the Interaction Between Promazine Hydrochloride and Surfactant (Conventional/Gemini) Mixtures at Different Temperatures

In the present paper, the micellization of an amphiphilic drug, promazine hydrochloride, and gemini surfactants (16-s-16) with s = 4–6 and the monomeric hexadecyltrimethylammonium bromide (CTAB) counterparts has been examined conductometrically in the pure and mixed states in aqueous solutions at different compositions and temperatures (298.15–308.15 K). Dicationic gemini surfactants provide much better environment for the micellization behavior than the corresponding monocationic counterpart CTAB. The critical micelle concentration (cmc) values are lower than the cmc for ideal mixing, cmc id, suggesting attractive interactions between the two components in mixed micelles. The micellar mole fractions of surfactants, evaluated by different models, show greater contributions of surfactants in mixed micelles and increase with increasing concentrations of these surfactants. The negative values of β suggest synergism in the mixtures, which is highly beneficial as it reduces the total amount of surfactants required in a particular application, leading to reductions of cost and environmental impact. Activity coefficients (f 1 and f 2) are always less than unity showing nonideality in the systems. The data have been also used for evaluation of thermodynamic parameters.

Interaction of amphiphilic drug imipramine hydrochloride with gemini surfactants at different temperatures

Imipramine hydrochloride (IMP) is a drug which is amphiphilic. Its interaction with gemini surfactants 14-s-14 (s=4, 5, 6) has been investigated at different temperatures employing conductimetric measurements. The experimentally determined critical micelle concentration (cmc) values come out to be lower than the ideal values (cmcid — the cmc value at ideal mixing state) suggesting attractive interactions between the mixture components. The micellar mole fraction of surfactant in the mixed systems (X1Rub, X1M, X1Rod, X1S and X1id), evaluated by applying various proposed models, shows greater contribution of the gemini surfactants in mixed micelles. Interaction parameters (β) come out to be negative which suggests synergism in the mixtures — this is highly beneficial as it reduces the total amount and hence the cost and environmental effect for use of the gemini surfactants in a particular application. The component activity coefficients (f1 and f2) are always less than unity showing nonideality in the systems. Thermodynamic parameters for the mixed micellization process have also been evaluated and discussed.

Synthesis of Al-substituted MCM-41 and MCM-48 solid acids with mixed cationic–anionic surfactants as templates

Al-substituted MCM-41 and MCM-48 (Al-MCMs in short) are potential solid acid catalysts for cracking long-chain alkanes to make lower-carbon alkenes. This work demonstrates the mixed cationic–anionic templating route as a low-cost method to make regular Al-MCMs with Al-enriched channel surface. Surface Al-enrichment is due to the interaction between Al3+ and COO− head group of anionic surfactant in mixed micelles during the formation of mesostructured precursors of Al-MCMs. Al-MCM-41 has a particularly higher amount of aluminum on its channel surface than Al-MCM-48. Therefore, Al-MCM-41 contains more and stronger acid sites and exhibits better activity in acid-catalyzed cracking of long-chain alkanes.

Computer Simulation–Molecular-Thermodynamic Framework to Predict the Micellization Behavior of Mixtures of Surfactants: Application to Binary Surfactant Mixtures

We present a computer simulation-molecular-thermodynamic (CSMT) framework to model the micellization behavior of mixtures of surfactants in which hydration information from all-atomistic simulations of surfactant mixed micelles and monomers in aqueous solution is incorporated into a well-established molecular-thermodynamic framework for mixed surfactant micellization. In addition, we address the challenges associated with the practical implementation of the CSMT framework by formulating a simpler mixture CSMT model based on a composition-weighted average approach involving single-component micelle simulations of the mixture constituents. We show that the simpler mixture CSMT model works well for all of the binary surfactant mixtures considered, except for those containing alkyl ethoxylate surfactants, and rationalize this finding molecularly. The mixture CSMT model is then utilized to predict mixture CMCs, and we find that the predicted CMCs compare very well with the experimental CMCs for various binary mixtures of linear surfactants. This paper lays the foundation for the mixture CSMT framework, which can be used to predict the micellization properties of mixtures of surfactants that possess a complex chemical architecture, and are therefore not amenable to traditional molecular-thermodynamic modeling.