Total Surfactant Concentration Research Articles

The study of micellar transitions in mixed systems of dibranched cationic/nonionic fluorinated surfactants using various physicochemical methods

AbstractIn this study, a new method was introduced to induce micellar transitions by using vesicles formed from mixed surfactants, which offer enhanced stability. Different physicochemical analysis methods were used to study the transition mechanism and the aggregation behavior of the mixed aqueous system composed of the double‐chain cationic didodecyldimethylammonium bromide (DDAB) and a single‐chain nonionic fluorinated surfactant undecafluoro n‐pentyl decaoxyethylene ether (C5F11(EO)10), by varying the fraction of DDAB, then the total surfactant concentration of DDAB/C5F11(EO)10 mixed system at XDDAB = 0.9. The obtained results indicated that the addition of the fluorinated surfactant C5F11(EO)10 to the mixed system resulted in a reduction of the surface tension (γ) and a decrease in the Electrical conductivity (K). Furthermore, even at high total concentrations of the mixed system, the conductivity and charge density at the surface remained stable. As XDDAB values increased, a higher degree of dissociation (α) was observed, along with negative values in the thermodynamic parameters of micellization (Δ, Δ, and Δ), confirming the transition from micelles to vesicles. The dynamic light scattering (DLS) analysis revealed the formation of two stable types of aggregates at both low and high concentrations, as supported by the zeta potential (ζ). Upon increasing the concentration of surfactants, UV–Vis absorption measurements indicated that small spherical micelles grow into large multilamellar vesicles, as evidenced by an increase in turbidity and confirmed transmission electron microscopy images.

Rheology and surface active properties of sodium N-lauroyl sarcosinate in mixed surfactant system

Anionic surfactant sodium N-lauroyl sarcosinate (SNLS) forms elongated wormlike micelles with cocamide monoethanolamine (CMEA) and lauryl glucoside (LG) a nonionic surfactants in the pH range 5.5–6.0. The total surfactant concentration was examined between 10% and 20% wt/v, and the pH was lowered from 7.5 to 4.5. The presence of CMEA/LG diminishes electrostatic repulsion amid SNLS head groups and prompts micellar transition displaying moderate viscosity. The viscosity peak of each system occurred in the pH range 5.5–5.8, close to the system’s pKa. This might prove to be a novel approach for SNLS surfactant formulation which otherwise was difficult to thicken. Additionally, mixed surfactant systems of SNLS/CMEA/LG portrays high surface activity, enhanced foaming behavior and improved skin mildness. Further, this study demonstrated a cost-effective and thickener-free method for cleansing compositions with the desired viscosity.

Concentration Dependent Asymmetric Synergy in SDS-DDAO Mixed Surfactant Micelles.

We investigate the structure and interactions of a model anionic/amphoteric mixed surfactant micellar system, namely, sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO), employing SANS, FTIR, DLS, and pH measurements, in the range 0.1-100 mM total surfactant concentration and 0-100% DDAO. Increasing surfactant concentration is found to elongate the prolate ellipsoid micelles (RPolar ∼ 25-40 Å), accompanied by up to a 6-fold increase in micellar charge. The surfactant synergy, in terms of micellar charge and size, diffusion coefficient, solution pH, and headgroup interactions, was found to vary with concentration. At lower concentrations (≤50 mM), the SDS-DDAO ratio of maximum synergy is found to be asymmetric (at 65-85% DDAO), which is rationalized using regular solution theory, suggesting an equilibrium between Na+ dissociation, DDAO protonation, and counterion concentration. At higher concentrations, maximum synergy shifts toward the equimolar ratio. Overall, our study expands and unifies previous reports, providing a comprehensive understanding for this model, synergetic mixed micellar system.

Impact of the Amphoteric Nature of a Chelating Surfactant on its Interaction with an Anionic Surfactant: A Surface Tension and Neutron Reflectivity Study of Binary Mixed Solutions.

2-Dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) is a chelating, amphoteric surfactant with a bulky headgroup containing eight pH-responsive groups. The hypothesis was that the amphoteric nature of the chelating surfactant would affect the interaction with another surfactant and, consequently, also the composition of mixed surface layers. Binary mixed monolayers of C12-DTPA and the anionic surfactant sodium dodecyl sulfate (SDS) were examined using neutron reflection and surface tension measurements. The experiments were conducted at pH 5, where the C12-DTPA monomers carried a net negative charge. Surface excess calculations at low total surfactant concentration revealed that the chelating surfactant dominated the surface composition. However, as the concentration was raised, the surface composition shifted toward an SDS-dominant state. This phenomenon was attributed to the increased ionic strength at increased concentrations, which altered the balance between competing entropic forces in the system. Interaction parameters for mixed monolayer formation were calculated, following a framework based on regular solution theory. In accordance with the hypothesis, the chelating surfactant's ability to modulate its charge and mitigate repulsive interactions in the surface layer resulted in favorable interactions between the anionic SDS and negatively charged C12-DTPA monomers. These interactions were found to be concentration-dependent, which was consistent with the observed shift in the surface layer composition.

QbD-assisted optimisation of liposomes in chitosan gel for dermal delivery of aceclofenac as synergistic approach to combat pain and inflammation.

Aceclofenac (ACE) is a drug that was precisely devised to circumvent the shortcomings associated with diclofenac. However, ACE too corresponds to nonsteroidal anti-inflammatory drug (NSAID)-related adverse effects, but with a lower amplitude. The present investigation seeks to develop liposomes loaded with ACE adopting a central composite design (CCD) and formulate a chitosan-based hydrogel for synergistic anti-inflammatory efficacy and improved ACE dermal administration. On the basis of preliminary vesicle size, Poly Dispersity Index (PDI), and drug entrapment, the composition of lipid, cholesterol, and vitamin E TPGS were chosen as independent variables. The formulation composition met the specifications for an optimum liposomal formulation, with total lipid concentration (13.5% w/w), cholesterol concentration (10% w/w), and surfactant concentration (2% w/w). With particle size and PDI of 174.22 ± 5.46nm and 0.285 ± 0.01 respectively, the optimised formulation achieved an entrapment effectiveness of 92.08 ± 3.56%. Based on the CCD design, the optimised formulation Acec-Lipo opt was chosen and was subsequently transformed to a chitosan-based gel formulation for in vitro drug release, penetration through the skin, in vivo analgesic therapeutic activity, and skin irritation testing. % age oedema inhibition was found to be greatest with the Acec-Lipo opt gel formulation, followed by Acec gel. These results reinforce the notion that the inclusion of chitosan resulted in a synergistic effect despite the same strength of the drug. The findings suggested that Acec-Lipo incorporated in chitosan gel for skin targeting might be an effective formulation for topical ACE administration in clinical subjects.

Wormlike micellar solutions formed by an anionic surfactant and a cationic surfactant with two head groups.

Innovation in the molecular structure of surfactants is important for the preparation of soft materials with novel properties. In this study, we synthesized a cationic surfactant, N1,N1,N1,N1,N3,N3,N3-pentamethyl-N3-(3-stearamidopropyl)propane-1,3-diammonium bromide, hereafter referred to as C18-DQA. Unlike conventional cationic surfactants, C18-DQA contains two quaternary ammonium head groups and a long-saturated alkyl chain equal to a chain length of 21 carbon atoms. C18-DQA exhibits a low Krafft point of ∼0 °C and a water solubility >1000 mM at 25 °C. The critical micelle concentration (cmc) of C18-DQA was determined to be 0.59 mM using the Nile red method. C18-DQA was mixed with sodium laurate (SL) at different molar ratios to produce transparent solutions with excellent viscoelasticity over a wide concentration range. The 1 : 1.5 molar ratio C18-DQA/SL mixed solutions exhibited gel-like behavior for a total surfactant concentration of 2.88 wt% (75 mM). The solution with a total surfactant concentration of 300 mM (120 mM C18-DQA and 180 mM SL) achieved a maximum zero-shear viscosity (η0) of 4224 Pa s. Cryogenic transmission electron microscopy analysis revealed the formation of extremely long wormlike micelles, with a cross-sectional diameter of 5 nm and contour length >3 μm, in the mixed solutions. C18-DQA and SL molecules were drawn close by electrostatic attractions, leading to a suitable molecular geometry for the extensive growth of wormlike micelles. This work will act as an important reference for the future preparation of highly viscoelastic solutions by mixing cationic and anionic surfactants. The proposed system is also expected to have potential applications in cosmetic formulations, home care products, and oilfield fracturing fluids.

Aqueous two-phase system based on benzethonium chloride and sodium dihexyl sulfosuccinate for extraction and ICP-OES determination of heavy metals

An aqueous two-phase system (ATPS) based on benzethonium chloride (BztCl) and sodium dihexyl sulfosuccinate (NaDHSS) was proposed for the first time for liquid-liquid microextraction of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), and Pb(II) followed by ICP-OES determination. The mixture of cationic and anionic surfactants, BztCl and NaDHSS, showed liquid-liquid phase separation at the molar ratio of 1:1, and the total surfactant concentration of 0.01–0.2 mol L−1 forming ATPS that was investigated in the extraction process. The extraction efficiency for Cd(II), Co(II), Mn(II), Ni(II), and Pb(II) was nearly 100 %, and for Cu(II) – not lower than 88 % in the presence of 8-hydroxyquinoline as a complexing agent. The surfactant-rich phase containing analytes was subjected to back-extraction with 0.2 M HNO3 before ICP-OES measurements. The preconcentration in the proposed BztCl–NaDHSS–H2O ATPS for 30 s and the high degree of back-extraction, which was achieved in 1 min, significantly reduced the sample preparation time, matrix effects and provided low LODs in the range of 0.04–1.0 μg L−1, the preconcentration factor was 120. The analysis of a certified reference material sample of surface water and the real samples of tap, sea, and waste water verified the method accuracy.

Surface-Area-to-Volume Ratio Determines Surface Tensions in Microscopic, Surfactant-Containing Droplets.

The surface composition of aerosol droplets is central to predicting cloud droplet number concentrations, understanding atmospheric pollutant transformation, and interpreting observations of accelerated droplet chemistry. Due to the large surface-area-to-volume ratios of aerosol droplets, adsorption of surfactant at the air-liquid interface can deplete the droplet's bulk concentration, leading to droplet surface compositions that do not match those of the solutions that produced them. Through direct measurements of individual surfactant-containing, micrometer-sized droplet surface tensions, and fully independent predictive thermodynamic modeling of droplet surface tension, we demonstrate that, for strong surfactants, the droplet's surface-area-to-volume ratio becomes the key factor in determining droplet surface tension rather than differences in surfactant properties. For the same total surfactant concentration, the surface tension of a droplet can be >40 mN/m higher than that of the macroscopic solution that produced it. These observations indicate that an explicit consideration of surface-area-to-volume ratios is required when investigating heterogeneous chemical reactivity at the surface of aerosol droplets or estimating aerosol activation to cloud droplets.

Design of PLGA nanoparticles for sustained release of hydroxyl-FK866 by microfluidics

The use of nanoparticle (NP) delivery systems in cancer treatment has received significant interest, however use of such systems in delivery of cytotoxic chemotherapy agents can be limited by low encapsulation efficiency and burst release of the cytotoxin, as well issues with throughput and reproducibility during the fabrication of drug-loaded NPs. In this study, we used a hydrodynamic flow-focusing microfluidic system to successfully produce poly(lactic-co-glycolic acid) (PLGA) NPs. The physico-chemical properties of PLGA NPs were controlled by changing the manufacturing parameters, such as flow rate ratio, total flow rate, PLGA and surfactant concentration. The NAMPT inhibitor-polymer conjugate, hydroxyl-FK866-PLGA, was synthesized and used to fabricate hydroxyl-FK866-PLGA NPs for the formulation of localized delivery systems able to release low doses of cytotoxins and enhance the efficacy of NAMPT inhibitors. Hydroxyl-FK866-PLGA NPs were prepared with optimized fabrication parameters, having average Z-size of 128 ± 8 nm (PDI < 0.2), ζ-potential of −14.8 ± 5.3 mV and high encapsulation efficiency (98.6 ± 5.8 %). The pH-dependent release of hydroxyl-FK866 was monitored over time in conditions mimicking the normal (pH 7.4) and inflamed/tumor (pH 6.4) microenvironments, observing a sustained release pattern (over two months) without any initial burst release. Finally, toxicity of hydroxyl-FK866-PLGA NPs were tested in selected human cell lines, the human leukemia monocytic cell line (THP-1), and the human triple negative breast cancer cell line (MDA-MB-231). Our work suggests that microfluidic systems are a promising technology for a rapid and efficient manufacturing of PLGA-based NPs for the controlled release of cytotoxins. Moreover, the use of drug-polymer conjugates is an effective approach for the manufacturing of polymeric NPs enabling high encapsulation efficiency and a prolonged and sustained pH-dependent drug release.

Self-Association of the Anion of 7-Oxodeoxycholic Acid (Bile Salt): How Secondary Micelles Are Formed.

Bile acid anions are steroidal biosurfactants that form primary micelles due to the hydrophobic effect. At higher concentrations of some bile acid anions, secondary micelles are formed; hydrogen bonds connect primary micelles. Monoketo derivatives of cholic acid, which have reduced membrane toxicity, are important for biopharmaceutical examinations. The main goal is to explain why the processes of formation of primary and secondary micelles are separated from each other, i.e., why secondary micelles do not form parallel to primary micelles. The association of the anion of 7-oxodeoxycholic acid (a monoketo derivative of cholic acid) is observed through the dependence of the spin-lattice relaxation time on total surfactant concentration T1 = f(CT). On the function T1 = f(CT), two sharp jumps of the spin-lattice relaxation time are obtained, i.e., two critical micellar concentrations (CMC). The aggregation number of the micelle at 50 mM total concentration of 7-oxodeoxycholic acid anions in the aqueous solution is 4.2 ± 0.3, while at the total concentration of 100 mM the aggregation number is 9.0 ± 0.9. The aggregation number of the micelle changes abruptly in the concentration interval of 80-90 mM (the aggregation number determined using fluorescence measurements). By applying Le Chatelier's principle, the new mechanism of formation of secondary micelles is given, and the decoupling of the process of formation of primary and secondary micelles at lower concentrations of monomers (around the first critical micellar concentration) and the coupling of the same processes at higher equilibrium concentrations of monomers (around the second critical micellar concentration) is explained. Stereochemically and thermodynamically, a direct mutual association of primary micelles is less likely, but monomeric units are more likely to be attached to primary micelles, i.e., 7-oxodeoxycholic acid anions.

Aqueous Two-Phase Systems Based on Cationic and Anionic Surfactants Mixture for Rapid Extraction and Colorimetric Determination of Synthetic Food Dyes.

In this study, aqueous two-phase systems (ATPSs) containing a cationic and anionic surfactants mixture were used for the preconcentration of the synthetic food dyes Allura Red AC, Azorubine, Sunset Yellow, Tartrazine, and Fast Green FCF. A rapid, simple, low cost, affordable, and environmentally friendly methodology based on microextraction in ATPSs, followed by spectrophotometric/colorimetric determination of the dyes, is proposed. The ATPSs are formed in mixtures of benzethonium chloride (BztCl) and sodium N-lauroylsarcosinate (NaLS) or sodium dihexylsulfosuccinate (NaDHSS) under the molar ratio close to equimolar at the total surfactant concentration of 0.01-0.20 M. The density, viscosity, polarity, and water content in the surfactant-rich phases at an equimolar ratio BztCl:NaA were determined. The effects of pH, total surfactant concentration, dye concentration, and time of extraction/centrifugation were investigated, and the optimum conditions for the quantitative extraction of dyes were established. The smartphone-based colorimetric determination was employed directly in the extract without separating the aqueous phase. The analytical performance (calibration linearity, precision, limits of detection and quantification, reproducibility, and preconcentration factor) and comparison of the spectrophotometric and smartphone-based colorimetric determination of dyes were evaluated. The method was applied to the determination of dyes in food samples and food-processing industrial wastewater.

Polyhedral oligomeric silsesquioxane as co-surfactant in stabilizing highly concentrated emulsion with an overcooled dispersed phase

This study investigated water-in-oil (w/o) super-concentrated emulsions used as pumpable explosives. The aqueous phase of the emulsions is a supersaturated nitrate salt solution (at room temperature), with a mass fraction of approximately 0.9. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report an alternative approach to stabilize emulsion explosives by using Polyhedral Oligomeric Silsesquioxane (POSS) as a co-surfactant to PIBSA (i.e. polyisobutylene succinic anhydride), in replacement of conventional co-surfactants, Span 80 or Tween 80. The interfacial tension, interfacial elasticity, refinement time, stability under high shearing as well as stability during storage have been investigated. It has been found that first, conversely to the standard co-surfactant Span 80, POSS can generate a more complex and very resistant interfacial film that has no tendency to induce crystallization in the system. Second, unlike conventional mixtures, PIBSA-MEA/POSS mixture confers outstanding stability to the emulsion not only under high shearing but most importantly during storage. In presence of POSS the emulsion explosives stabilization occurs through a reinforced interfacial skin rather than the usual mechanical barrier of reverse micelles in the inter-droplet layer. This new mechanism is much more effective than the conventional one and allows for a significant reduction in the total surfactant concentration required to stabilize the sheared as well as un-sheared emulsions. We propose that through the synergetic interaction POSS occupy the free spaces between the bulky polymeric PIBSA molecules and create a reinforced condensed layer at the interface.

Interfacial properties of cationic and anionic Gemini surfactant mixtures

AbstractThe possibility and the prospect of cationic/anionic (“catanionic”) surfactant mixtures based on sulfonate Gemini surfactant (SGS) and bisquaternary ammonium salt (BQAS) in the field of enhanced oil recovery was investigated. The critical micelle concentration (CMC) of SGS/BQAS surfactant mixtures was 5.0 × 10−6 mol/L, 1–2 orders of magnitude lower than neat BQAS or SGS. A solution of either neat SGS or BQAS, could not reach an ultra‐low interfacial tension (IFT); but 1:1 mol/mol mixtures of SGS/BQAS reduced the IFT to 1.0 × 10−3 mN/m at 100 mg/L. For the studied surfactant concentrations, all mixtures exhibited the lowest IFT when the molar fraction of SGS among the surfactant equaled 0.5, indicating optimal conditions for interfacial activity. The IFT between the 1:1 mol/mol SGS/BQAS mixtures and crude oil decreased and then increased with the NaCl and CaCl2 concentrations. When the total surfactant concentration was above 50 mg/L, the IFT of SGS/BQAS mixtures was below 0.01 mN/m at the studied NaCl concentrations. Adding inorganic salt reduced the charges of hydrophilic head groups, thereby making the interfacial arrangement more compact. At the NaCl concentration was above 40,000 mg/L, surfactant molecules moved from the liquid–liquid interface to the oil phase, thus resulting in low interfacial activity. In addition, inorganic salts decreased the attractive interactions of the SGS/BQAS micelles that form in water, decreasing the apparent hydrodynamic radius (DH, app) of surfactant aggregates. When the total concentration of surfactants was above 50 mg/L, the IFT between the SGS/BQAS mixtures and crude oil decreased first and then increased with time. At different surfactant concentrations, the IFT of the SGS/BQAS mixtures attained the lowest values at different times. A high surfactant concentration helped surfactant molecules diffuse from the water phase to the interfacial layer, rapidly reducing the IFT. In conclusion, the cationic‐anionic Gemini surfactant mixtures exhibit superior interfacial activity, which may promote the application of Gemini surfactant.

Revealed Properties of Various Self-Assemblies in Two Catanionic Surfactant Systems in Relation to Their Polarity and Molecular Packing State.

A catanionic surfactant system is an aqueous solution or dispersion of cationic and anionic surfactants that spontaneously self-assemble into structures such as micelles, vesicles, and coacervates. Their structural diversity varies depending on the ratios of cationic and anionic surfactants (compositions), the chemical structure of the constituent molecules, etc. Herein, two types of catanionic surfactant systems were systematically characterized: (i) cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), both typical ionic surfactants; and (ii) dodecylmethylimidazolium ammonium bromide ([C12mim]Br) and SDS, where the former is an ionic liquid. By observing the sample appearance, turbidity, and particle size, the phase state of each system was analyzed according to the total concentration of surfactants and the molar ratio of cationic surfactants to the total concentration. Especially, for specific compositions of catanionic surfactant vesicles (cataniosome), the closed structure of the vesicles was confirmed through calcein entrapment and release detected with a fluorescence assay. The polarities of the interface of the prepared self-assemblies were evaluated using a fluorescence probe, Laurdan. The packing state of the molecules in the formed self-assembly structure was estimated using Raman spectroscopy. The results clearly indicate consistent phase-transition behavior for the CTAB-SDS (i) and [C12mim]Br-SDS (ii) systems, depending on the total surfactant concentration and composition, while the membrane properties of the two systems differed. The cataniosome formed in the CTAB-SDS system was in a tightly packed membrane state and more hydrophobic than that formed in the [C12mim]Br-SDS system owing to the difference in the structure of the constituting molecule: [C12mim]Br has a larger head group and shorter acyl chain than CTAB. The self-assembly properties evaluated in this study were compared with those of typical lipid membranes, liposomes (lipid vesicles), to determine a possible application of the catanionic systems with various self-assembly formulations.

A Recent Review on Bio-availability Enhancement of Poorly Water-soluble Drugs by using Bioenhancer and Nanoparticulate Drug Delivery System.

Intravenous route of drug administration has maximum bioavailability, which shows 100% of the drug reaches blood circulation, whereas the oral administration of drugs, are readily undergoing pre-systemic metabolism, which means the poor bioavailability of the drug and limited amount of drug reaches the target site. Bioenhancers are substances having medicinal entities which enhance the bioavailability and efficacy of the active constituents of drugs. The enhanced bioavailability of drugs may lead to dose reduction, which may further reduce the cost and undesired side effects associated with the drugs. The solid lipid nanoparticles (SLNs) loaded with ketoprofen made from carnauba wax and beeswax. It was discovered that when the drug-loaded SLNs were mixed with egg-lecithin and Tween-80, as well as when the total surfactant concentration was increased, the average particle size of the drug-loaded SLNs decreased. The drug-loaded nanoparticles, when given in combination with bio-enhancers such as piperine and quercetin, enhanced the drug's effectiveness. The Area Under Curve (AUC) was increased when the drug was coupled with bio-enhancers. Based on the findings, it can be concluded that piperine and quercetin when used with drug-loaded nanoparticles improve their therapeutic effectiveness. Bioenhancers are crucial to amplifying the bioavailability of many synthetic drugs. These attributes are useful to reduce the dose of drugs and increase the therapeutic efficacy of drugs with poor bioavailability.

Wettability alteration and reducing water blockage in tight gas sandstone reservoirs using mixed cationic Gemini/nonionic fluorosurfactant mixtures

AbstractThe unrecovered hydraulic fracturing fluid will invade the matrix and induce water blockage, creating formation damage and hindering the oil or gas production rate. First, the synergistic effect of cationic Gemini surfactant (MQAS) and nonionic fluorosurfactant (N‐2821) mixtures on reducing the surface tension and wettability alteration was investigated in this paper. The critical micelle concentration (CMC) of the surfactant mixture is one or two orders of magnitude lower than that of N‐2821 and MQAS, indicating that the MQAS/N‐2821 mixtures exhibit an apparent synergistic effect in reducing surface tension. Moreover, the maximal contact angle of MQAS/N‐2821 mixtures reached 83.55° at αN‐2821 = 0.5, and the total surfactant concentration of 1 × 10−4 mol/L due to the adsorption of surfactant. The adsorption mechanism of surfactants on the surface of quartz sand was then examined. The adsorption kinetics is consistent with the pseudo‐second‐order model at different surfactant concentrations, while the Freundlich model is suitable for describing the adsorption behavior of surfactants on the sandstone surface. This finding indicates that surfactant adsorption is multilayered. The MQAS/N‐2821 surfactant mixtures have excellent surfactant activity due to the relationship of the capillary pressure to the surface tension, pore radius, and contact angle; thus, the addition of surfactant mixtures can reduce the liquid saturation effectively. Furthermore, the sequential imbibition experiments indicate that MQAS/N‐2821 mixtures alter the wettability of the core plug, which results from the adsorption of surfactants. Compared with brine water, the MQAS/N‐2821 mixtures decreased the liquid saturation and increased the permeability recovery ratios of the core plug.

Coarse-Grained Model Incorporating Short- and Long-Range Effective Potentials for the Fast Simulation of Micelle Formation in Solutions of Ionic Surfactants.

A coarse-grained model comprising short- and long-range effective potentials, parametrized with the iterative Boltzmann inversion (IBI) method, is presented for capturing micelle formation in aqueous solutions of ionic surfactants using as a model system sodium dodecyl sulfate (SDS). In the coarse-grained (CG) model, each SDS molecule is represented as a sequence of four beads while each water molecule is modeled as a single bead. The proposed CG scheme involves ten potential energy functions: four of them describe bonded interactions and control the distribution functions of intramolecular degrees of freedom (bond lengths, valence angles, and dihedrals) along an SDS molecule while the other six account for intermolecular interactions between pairs of SDS and water beads and control the radial distribution functions. The nonbonded effective potentials between coarse-grained SDS molecules extend up to about 12 nm and capture structural and morphological features of the micellar solution both at short and long distances. The long-range component of these potentials, in particular, captures correlations between surfactant molecules belonging to different micelles and is essential to describe ordering associated with micelle formation. A new strategy is introduced for determining the effective potentials through IBI by using information (target distribution functions) extracted from independent atomistic simulations of a micellar reference system (a salt-free SDS solution at total surfactant concentration cT equal to 103 mM, temperature T equal to 300 K, and pressure P equal to 1 atm) obtained through a multiscale approach described in an earlier study. It employs several optimization steps for bonded and nonbonded interactions and a gradual parametrization of the short- and long-range components of the latter, followed by reparametrization of the bonded ones. The proposed CG model can reproduce remarkably accurately the microstructure and morphology of the reference system within only a few hours of computational time. It is therefore very promising for future studies of structural and morphological behavior of various liquid surfactant formulations.

Novel approach for tuning micellar characteristics and rheology of a sulfate-free anionic surfactant sodium cocoyl glycinate

Amino acid based mild and sulfate-free anionic surfactant, sodium cocoyl glycinate (SCGLY) forms spherical micellar aggregates in water. The mixed micellar characteristics of SCGLY has been studied in the presence of nonionic surfactants like cocamide diethanolamine (CDEA) and lauryl glucoside (LG). The ternary aqueous system of SCGLY/CDEA/LG depicts higher surface activity and stronger aggregation ability compared to corresponding single or binary surfactant systems as revealed by tensiometry. The effect of pH (5.5–6.5) and total surfactant concentration (14–18 wt%) on thickening of SCGLY/CDEA/LG system is studied by rheology measurements. The presence of CDEA/LG amid charged SCGLY head group shrinks the electrostatic repulsion and induces sphere-to-rod micellar transition depicting low or moderate viscosity under as-prepared neutral pH. With alteration in pH, viscosity augmented to a maximum (at pH ~5.8) followed by a viscosity decrease. This is a novel finding for mild sulfate-free SCGLY surfactant solution which otherwise is very hard to thicken. Micellar size and charge is attained by dynamic light scattering, while micellar shapes and aggregation numbers are determined by small-angle neutron scattering (SANS) measurements. Moreover, foaming behavior (foamability and stability) and mildness property (zein solubility) of SCGLY can be optimized as per the necessity in the presence of CDEA and LG. This work might prove to be an innovative approach to tune the micellar characteristics and rheology of amino acid based surfactant formulation which could be extremely beneficial for cost-effective, thickener-free, sulfate-free surfactant systems used in cleansing composition with desired viscosity.

The high-concentration stable phase: The breakthrough of catanionic surfactant aqueous system

Precipitates occur readily in the aqueous mixture of cationic and anionic surfactants. We report that the precipitates formed in the catanionic surfactant systems at charge ratios deviated from 1:1 can be solubilized by simply increasing the total surfactant concentrations. At higher concentrations, there are vesicles in the supernatant, which will sequester the monomer surfactant in equilibrium with the precipitates. This shifts precipitation-solvation equilibrium continuously. As a result, the precipitates vanish when all the surfactants in the precipitates are taken into the vesicles. In this way, a high-concentration stable phase (HCSP) can be formed in the precipitated surfactant systems, which can be generalized to all catanionic surfactant systems. We envision the concentration-triggered HCSP is very promising in guiding the large-scale application of catanionic surfactants.

Sodium dodecyl benzene sulfonate (SDBS) and N,N-dimethyldodecan-1-amine oxide (DDAO) in single and mixed systems as corrosion inhibitors of zinc in hydrochloric acid

Abstract The influence of surfactant synergism between sodium dodecyl benzene sulfonate (SDBS) and N,N-dimethyldodecan-1-amine Oxide (DDAO) on zinc corrosion in 0.05 M hydrochloric acid (HCl) solutions at 25 °C was investigated. Firstly, solutions of SDBS and DDAO with mole fractions of 0.00, 0.25, 0.50, 0.75 and 1.00 were prepared and their surface tension and critical micelle concentration (CMC) values in water and in 0.05 M HCl were measured as a function of total surfactant concentration. The SDBS/DDAO mixed system exhibited a strong synergism in 0.05 M HCl with a highly negative interaction parameter β (average β = −23.46), according to regular solution theory. Secondly, the adsorption of single surfactants SDBS and DDAO and SDBS/DDAO surfactant mixture on 2.0% zinc powder was investigated by the depletion method to find out the role of synergism in the adsorption tendency of these surfactants on the zinc surface and thus their corrosion inhibiting effect. The adsorption tendency of single surfactant and the mixed surfactant systems onto 2.0% zinc powder followed the order: SDBS &gt; 0.75 SDBS/0.25 DDAO ≈ 0.25 SDBS/0.75 DDAO &gt; DDAO &gt; 0.50 SDBS/0.50 DDAO. Finally, the corrosion of zinc was investigated using the potentiodynamic polarization technique. It was found that SDBS and DDAO act as efficient corrosion inhibitors for zinc in 0.05 M HCl solution with increasing corrosion inhibition efficiency when they are mixed. Additionally, images of scanning electron microscopy were obtained for zinc sheets in solutions containing single and mixed SDBS/DDAO surfactants in the presence and absence of 0.05 M HCl. The microscopic images show an improvement in the protection of the zinc surface against acid attack in the presence of single and mixed SDBS/DDAO surfactants.