Single Surfactant Systems Research Articles

Interaction mechanism and compatibility studies of silk protein peptide (SPP) with the common surfactants SDS and DTAB

The molecular interaction of low-molecular-weight SPP with common surfactants (SDS and DTAB) is a more complicated process than has been long believed. In this work, the interaction mechanism between SDS/DTAB and SPP was proposed using multiple methods including conductivity measurements, ST, UV-vis, FT-IR, DLS, fluorescence spectroscopy, and molecular docking simulations. Moreover, the foaming properties of the mixed systems were studied, and they were evaluated as cosmetics preservatives. The effects of various surfactant and protein concentrations and ratios on compatibility and functionality were studied. Based on the results, the mechanism of complex formation was identified as a cooperative van der Waals interaction followed by hydrophobic interaction and hydrogen bonding. A simpler head group leads to easier aggregation and interaction with the SPP, the formation of smaller-sized complexes, and a weaker impact on the fluorescence intensity. Thus, SDS monomers easily aggregate on SPP chains, leading to a stronger influence on the final secondary structure of SPP. This was confirmed by multiple spectroscopy methods. Comparing its single surfactant system, the SDS-SPP solution demonstrates better foaming power and the DTAB-SPP solution shows higher bacteriostatic activity. The good compatibility between SDS/DTAB and SPP can improve the functional properties of SDS or DTAB as well as lower the optimal concentration of each component. These results provide data and theoretical support for the design of cosmetic product formulas.

The aggregation structure and rheological properties of catanionic surfactant mixtures and potential applications in fracturing fluids

Clean fracturing fluids are widely used in reservoir stimulation and increasing production due to their characteristics of simple preparation, no residue, easy flowback, and low damage. At present, clean fracturing fluids are mainly prepared by cationic surfactants as main agent and inorganic or organic salts as additives, which can lead to unavoidable losses of cationic surfactants due to their adsorption in the formation. Anionic-cationic surfactants composite system can not only compensate for the shortcomings of a single surfactant system, but also improve the reservoir adaptability of the surfactant system. In this paper, a clean fracturing fluid was prepared with long-chain anionic surfactant, Sodium erucate (NaOEr), as main agent and a series of cationic surfactants with different as additive. Then, the aggregation behavior of mixed system was determined by visual appearance, rheology experiments, differential scanning calorimetry and cryogenic transmission electron microscopy. The phase transition mechanism induced by temperature was proposed, and the performance of the mixed system as a fracturing fluid was evaluated. The results showed the mixed systems could self-assemble into wormlike micelles when the length of hydrophobic carbon chains of cationic surfactant was 6 and 8. Increasing the length of the hydrophobic carbon chain could enhance the electrostatic effect, leading to precipitation in the mixed system. When the ratio of cationic surfactant was between 0.5 and 0.6 and the concentration was between 68 and 175 mmol∙L-1, the mixed systems tended to form three-dimensional structures by entangling and stacking wormlike micelles, showing high viscoelasticity and viscosity. The aggregation structure of the mixed system transformed from vesicles to wormlike micelles at 46.8 °C, which is attributed to the transition of carbon chains of NaOEr from non-flexible to flexible. Finally, the mixed system as a fracturing fluid has good shear resistance and temperature resistance. The viscosity of NaOEr/HTAB can reach above 50 mPa⋅s after sheared for 60 min at the conditions of 170 s−1 and 80 °C. This study provides an anionic clean fracturing fluid and broaden the application of viscoelastic surfactants in oilfield development.

Surfactant Micelle-Driven High-Efficiency and High-Resolution Length Separation of Carbon Nanotubes for Electronic Applications.

High-efficiency extraction of long single-wall carbon nanotubes (SWCNTs) with excellent optoelectronic properties from SWCNT solution is critical for enabling their application in high-performance optoelectronic devices. Here, a straightforward and high-efficiency method is reported for length separation of SWCNTs by modulating the concentrations of binary surfactants. The results demonstrate that long SWCNTs can spontaneously precipitate for binary-surfactant but not for single-surfactant systems. This effect is attributed to the formation of compound micelles by binary surfactants that squeeze the free space of long SWCNTs due to their large excluded volumes. With this technique, it can readily separate near-pure long (≥500nm in length, 99% in content) and short (≤500nm in length, 98% in content) SWCNTs with separation efficiencies of 26% and 64%, respectively, exhibiting markedly greater length resolution and separation efficiency than those of previously reported methods. Thin-film transistors fabricated from extracted semiconducting SWCNTs with lengths >500nm exhibit significantly improved electrical properties, including a 10.5-fold on-state current and 14.7-fold mobility, compared with those with lengths <500nm. The present length separation technique is perfectly compatible with various surfactant-based methods for structure separations of SWCNTs and is significant for fabrication of high-performance electronic and optoelectronic devices.

Study on the properties of branched-chain alkyl glycoside nonionic surfactant and anionic surfactant in a mixed system

Abstract The surface activity, intermolecular interactions and thermodynamic parameters of a mixture of a nonionic surfactant (branched-chain alkyl glycoside (IG-10)) and an anionic surfactant (alcohol ether carboxylic acid (90H)) were investigated and the wetting, emulsifying and foaming properties of the mixed system were also evaluated. The results show that there is a mutual attraction at the mixed micelles and gas/liquid interfaces formed by the two surfactants. The thermodynamic parameters show that the formation of mixed micelles from two different surfactants is a non-ideal process. In terms of application performance, the wetting ability and foaming properties of the mixed system showed good synergistic effects, with the wetting time of the mixed system being shorter than that of the two single surfactant systems and the foam stability being weaker than that of the single system. The best emulsifying capacity was obtained when the mass fraction of 90H was 50 %.

Effect of interfacially-engineered nanoemulsions of linoleic acid stabilized by mixed surfactant systems and curcumin on their physicochemical properties, induction times, and peroxidation stability

Nanoemulsions have become the best candidates for loading hydrophobic bioactive molecules and enhancing their shelf-life and bioavailability in the food, pharmaceutical and cosmetic industries. Mixture of different surfactants modulates their interfacial characteristics, thereby imposing a direct effect in improving their physicochemical and nutritional characteristics. Herein, we report the formulation of oil-in-water nanoemulsions stabilized with either single or mixture of surfactants having different electric charges like Tween 20 (T20, nonionic), sodium salt of Lauroyl Sarcosine (LS, anionic) and 3-(N,N-dimethylmyristylammonio)propanesulfonate (DPS, zwitterionic) to control the peroxidation of linoleic acid by using curcumin as the potential antioxidant. The distribution of H+ ions at the interface and the variation in the values of observed rate constant (kobs) is assessed by employing the novel Chemical Kinetic method based on the reaction between arenediazonium ions and the antioxidant. For single-surfactant systems, nanoemulsions containing pure T20 or LS showed good oxidative stability whereas for mixed-surfactant systems, the oxidative stability increases with increasing concentration of LS and decreasing concentration of DPS. This could be explained on the basis of physicochemical characterization of nanoemulsions, interfacial H+ ion concentration, and solubility characteristics of curcumin. The study shows great promise of such mixed surfactant systems, ignored so far, for providing a novel and tailored formulation of nanoemulsions for improving the oxidative stability of linoleic acid.

Chemical Demulsification of Oil-in-Water Emulsion from Gas Condensate Field

Produced water, also known as oily wastewater, is one of the major wastes in the oil and gas industry. During the hydrocarbon production, formation of emulsion takes place such as oil-in-water emulsion which has a huge financial effect on the sector. Oil and gas industry seeks highly effective and reasonable demulsifying chemicals to separate the oil-in-water emulsions into water and crude oil. Thus, in this publication, resin alkoxylate, cationic polyamine, cationic surfactant and ethylene oxide/propylene oxide (EO/PO) block copolymers are utilized to resolve the oil-in-water emulsion from a gas condensate field. According to the findings of preliminary screening, a unique demulsifier DB was formulated by incorporating resin alkoxylate and cationic surfactant at an optimal weight percentage ratio. Demulsification efficiency (De) of 96 % based on measurement of turbidity was attained after treating the oil-in-water (O/W) emulsion with demulsifier DB at a dosage of 7 ppm. To determine the demulsifier's efficiency further, the oil-in-water content (OiW) of the produced water was evaluated after the treatment with demulsifier DB. Oil removal efficiency (ORe) of 90% was achieved as the formulated demulsifier DB reduced the oil-in-water content (OiW) of O/W emulsion from 1008.3 ppm to 97.1 ppm within 15 minutes at the dosage of 7 ppm. Furthermore, interfacial tension (IFT) and Turbiscan analysis were performed to further study the demulsification process of blank sample and the addition of the demulsifier DB at the optimized dosage of 7 ppm. At demulsifier DB dosage of 7 ppm, the interfacial tension between oil and water reduced significantly compared to blank sample from 24.98 mN/m to 9.38 mN/m. The produced water sample after treatment with 7 ppm of demulsifier DB resulted in a significant increase of Turbiscan Stability Index (TSI) value of 8 which indicates the rate at which the separation of oil and water occurred. The attained results of IFT and Turbiscan analysis further validate that mixed surfactant system is more efficient than single surfactant system. By combining surfactants with different functional groups, mixed surfactant systems can exhibit greater surface activity than single surfactants.

Critical micelle concentration and partition coefficient of mixed micelles: Analysis of ternary systems based on Markov chain model and simple mixture model

When two or more surfactants are mixed, the mixed system exhibits improved performance compared with a single surfactant system in solution. The Markov chain model can analyze the critical micelle concentration (CMC) of mixed micelles, yielding results similar to those of a simple mixture model, which is typically referred to as the “regular solution theory”. In this study, two hypotheses were tested: (1) the Markov chain model for ternary systems can be simplified by approximating the association constant of surfactants i and j as Kij = Kji and (2) the quasi-simple ternary mixture model, that is, a simple mixture model analogous to the Markov chain model, helps interpret the interaction parameter of the simple mixture model that can describe the partition coefficient of the binary mixed micelle. Equations were derived for (1) the Markov chain model for ternary systems by assuming Kij = Kji and (2) the interaction parameter of the simple mixture model that can describe the partition coefficient of the binary mixed micelle. The models were compared with the experiment data, and the derived equations described the data of the CMC and partition coefficient well.

Comparison of a single pharmaceutical surfactant versus intestinal biorelevant media for etravirine dissolution: Role and impact of micelle diffusivity

Etravirine is an antiviral whose oral absorption is limited by low solubility/dissolution. The objective was to predict and compare etravirine’s surfactant-mediated dissolution into polyoxyethylene-10 lauryl ether (POE) and FeSSIF-V2, including the contribution of slow micelle diffusivity. Dynamic light scattering (DLS) was used to measure the size and diffusivity values of drug-loaded micelles. In vitro intrinsic dissolution into surfactant media were predicted using a model for surfactant-mediated dissolution. Compared to maleic buffer, POE and FeSSIF-V2 increased etravirine solubility 232-fold and 8.97-fold, respectively. From DLS, micelle diffusivity of drug-loaded POE micelle and FeSSIF-V2 mixed-micelle was 5.15x10−7 cm2/s and 5.76x10−8 cm2/s, respectively. Observed and predicted dissolution enhancement into POE were 50.7 and 31.3, and 1.26 and 1.24 into FeSSIF-V2, respectively. Hence, there was high dissolution enhancement into POE, although the observed enhancement was only 21.9% of the observed solubility enhancement, reflecting the attenuating impact of the large and slowly diffusing drug-loaded POE micelles. Meanwhile, there was minimal dissolution enhancement into FeSSIF-V2, and the observed enhancement was only 14.0% of the observed solubility enhancement, reflecting the even slower diffusing drug-loaded FeSSIF-V2 mixed-micelles compared to drug-loaded POE micelles. Results are considered in light of designing a single pharmaceutical surfactant system for dissolution that mimics a FeSSIF-V2 system.

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.

Marangoni spreading time evolution and synergism in binary surfactant mixtures

HypothesisMarangoni spreading driven by localized surfactant solution deposition previously has been studied only for single surfactant systems. For binary surfactant mixtures, interactions that generate surface tension synergism, a thermodynamic effect, may also synergistically enhance Marangoni spreading dynamics, introducing the concept of Marangoni synergism. Spreading dynamics and possible Marangoni synergism should depend not only on thermodynamic properties but also kinetic properties of the binary system. Experiments and modelingTracer experiments that capture post-deposition surfactant front motion were performed in parallel with computational modeling, using binary surfactant pairs with varying interaction strengths. The model coupled the Navier-Stokes and advective diffusion equations with a Frumkin-type binary adsorption model. FindingsWe confirm the existence of Marangoni synergism. Stronger binary surfactant attraction favors synergism in both surface tension reduction and Marangoni spreading. Binary composition ranges over which surface tension synergism occurs differ from those for Marangoni synergism, indicating that the origins of the two synergistic effects are not identical. Analysis of model spreading velocities show that the thermodynamic spreading parameter is the controlling factor at early times for both single and binary surfactant systems, while the intrinsic adsorption and desorption kinetics influence spreading velocities and thus the occurrence of Marangoni synergism at later times.

PH-Dependent Interfacial Tension and Dilatational Modulus Synergism of Oil-Soluble Fatty Acid and Water-Soluble Cationic Surfactants at the Oil/Water Interface.

While the concept of interfacial tension synergism in surfactant mixtures is well established, little attention has been paid to the possibility of synergistic effects on the interfacial rheology of mixed surfactant systems. Furthermore, interfacial tension synergism is most often investigated for mixtures of surfactants residing in a single phase. Here, we define dilatational modulus synergism and report a study of interfacial tension isotherms and complex dilatational moduli for a binary surfactant system with the two surfactants accessing the oil/water interface from opposite sides. Using an oil-soluble fatty acid surfactant (palmitic acid, PA) that may be ionized at the oil/water interface and a quaternary ammonium water-soluble cationic surfactant (tetradecyltrimethylammonium bromide, TTAB), the binary interfacial interaction was tuned by the aqueous phase pH. Interfacial tensions and dilatational moduli were measured by the pendant drop method for the binary surfactant system as well as the corresponding single-surfactant systems to identify synergistic effects. The possible occurrence of dilatational modulus synergism was probed from two perspectives: one for a fixed total surfactant concentration and the other for a fixed interfacial tension. The aqueous pH was found to have a controlling effect on both interfacial tension synergism and the dilatational modulus synergism. The conditions for interfacial tension synergism coincided with those for the storage modulus synergism: both tension and storage modulus synergisms were observed under all conditions tested at pH 7 where PA was mostly deprotonated, for both perspectives examined, but not for any conditions tested at pH 3 where PA is mostly protonated. The loss modulus synergism exhibited more complex behaviors, such as frequency and interfacial tension dependences, but again was only observed at pH 7. The tension and modulus synergism at pH 7 were attributed to the increased attraction between ionized PA and cationic TTAB and the formation of catanionic complexes at the oil/water interface.

New insights into the “unzippering” mechanism of carbon nanotube dispersion via the “trigger” effect of small charged molecules

In binary systems, the influence of different surfactants in carbon nanotube (CNT) dispersion and the dispersion efficiency remain unclear. This study compared CNT dispersion by sodium dodecyl benzene sulfonate (SDBS, small molecule), Triton X-100 (TX 100, large molecule), and their mixtures in single and mixed surfactant systems. A synergistic effect between SDBS and TX 100 was observed for CNT dispersion. The enhancement adsorption of TX 100 by SDBS indicated that SDBS likely acted as a trigger in the “unzippering” mechanism due to its small molecular size. The actual dispersion efficiency of CNT being higher than the theoretical value also proved the trigger effect of SDBS. However, when TX 100 concentration exceeded its critical micelle concentration, the synergistic effect disappeared. This result indicated that the trigger effect of SDBS probably did not occur because TX 100 directly encapsulated CNT in the form of large micelles.

PH Changes in the Micelle-Water Interface of Surface-Active Ionic Liquids Dictate the Stability of Encapsulated Curcumin: An Insight Through a Unique Interfacial Reaction between Arenediazonium Ions and t-Butyl Hydroquinone.

The chemical kinetic (CK) method, which involves the reduction of 4-hexadecylbenzenediazonium ions (16-ArN2+) by antioxidants (in the present case, TBHQ) occurring exclusively at the interface of the association colloids, was employed to establish the changes in the chemical reactivity of anionic surface-active ionic liquids (SAILs) as a function of the concentration and the composition in their mixed states. We used sodium dodecyl sulfate and different SAILs based on the dodecylsulfate surfactant containing 1-alkyl-3-methylimidazolium cations as counterions having a varying alkyl chain length of 4 (bmim), 8 (omim), and 12 (ddmim) carbon atoms. The structural transitions of aggregates of the SAILs from the micellar to vesicular form were observed as a function of concentration in single surfactant systems and as a function of composition in mixed surfactant systems. Results of the reduction kinetics of 16-ArN2+ at the interface of such aggregates, which depends on the acid/base equilibria at the interface, gave an insight into the changes in the interfacial H+ ions with the change in the hydrophobicity of the counterions of SAILs and the morphological changes from micelles to vesicles as a function of concentration or composition. These changes in the interfacial pH correlate very well with the stability of curcumin within these self-assemblies, which exclusively depends on the pH of the medium and highlights the importance of the results obtained from the CK method in selecting the appropriate medium/conditions for the stabilization of the bioactive molecules.

Eucalyptus Oil-Based Nanoemulsion: A Potent Green Nanowagon for Controlled Delivery of Emamectin Benzoate

Formulating a biocompatible water-based pesticide and eliminating the use of toxic solvents encourage sustainable agriculture practices. In this study, a eucalyptus oil-in-water nanoemulsion (NEm) was employed as a green and biocompatible nanocarrier for the delivery of a water insoluble pesticide, emamectin benzoate (EB). NEm was prepared using low-energy emulsion phase inversion (EPI) and high-energy probe sonication (PS) with the help of food grade emulsifiers Tween 20 and Span 80. The effect of using a single or binary surfactant system and its effect on NEm droplet size and stability were investigated by measuring the change in droplet diameter for three months. The morphology, shape, and size of the NEm were assessed using high-resolution transmission electron microscopy, field emission scanning electron microscopy, and dynamic light scattering. Fourier transform infrared spectroscopy was employed to confirm the successful encapsulation of EB in the eucalyptus oil (EuO) core. During the investigation, the encapsulation efficiency of EPI NEm (91%) was higher than that of PS NEm (86%). The antiphotolysis and leaf adhesion ability of the EuO NEm was found to be better than those of free EB and the commercial EB formulation. Both NEms showed slow and sustained release compared to the commercial EB formulation, which shows a burst release. This implies EuO NEm behaves as a better pesticide formulation than free EB and its commercial analogue. However, EPI NEm with a higher encapsulation efficiency and a better release performance compared to those of PS NEm is considered a low-cost and easy-to-prepare nanoformulation. Thus, EB-loaded EuO NEm can be considered as a formulation that is greener, free of organic solvents, biocompatible, and easy to scale up for industrial application with promising sustainable agriculture development.

Study on the treatment of oily sludge in oil fields with lipopeptide/sophorolipid complex bio-surfactant

A systematic study had been carried out to get insight into the micellar behavior of anionic lipopeptide (LT) and nonionic sophorolipid (SL) in their different mass ratio mixed state using the technique of tensiometry. The models proposed by Clint, Rubingh and Gibbs et al. had been employed to interpret the formation of mixed micelles and found out synergism. The obtained experimental critical micelle concentrations (CMC) were lower than the ideal CMCs, indicating negative deviation from ideal behavior for all multi-component mixed micelles formation. A suited binary bio-surfactant mixing system was selected as the washing agents to treat the oily sludge produced from Huabei oilfield by the thermal bio-surfactant washing method. The results showed that in case of the mass ratios of 8:2 the CMC was dramatically decreased and synergism was the strongest in LT and SL bi mixed surfactant systems. The studied binary mixed bio-surfactant system showed higher washing efficiency for oily sludge than single surfactant system. In addition, the washing power of binary mixed bio-surfactants towards oily sludge was the best at below washing conditions: (a) the concentration of the mixed system (100 mg/L), (b) temperature (55 ℃), (c) ratio of sludge/liquid (1:3), (d) washing time (3 h), and (e) stirring speed (300 rpm). Certainly, the washing abilities of the selected surfactants not only depend on their mixing ratio and washing conditions but also associate with microstructure and mineral components of oily sludge.

Effect of Single/Mixed Surfactant Systems on Orientations of Liquid Crystals and Interaction of Proteins with Surfactants at Fluid Interfaces

A series of single surfactant systems, i.e, quaternary ammonium-based gemini surfactants with different spacers and alkyl chain lengths (m-n-m; m = 12, n = 2, 3, 4, 6; n = 3, m = 12, 14, 16), halogen-free surface-active ionic liquid (HF-SAILs) with different symmetries ([Cnmim][C12H25SO4]; n = 6, 8, 10, 12), and single-chain cationic surfactants including 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and dodecyltrimethylammonium bromide (DTAB), along with certain combinations of different surfactants (12-3-12/[C12mim]Br and 12-3-12/DTAB) were applied to an aqueous/liquid crystal interface (ALI). All the surfactants could induce an orientational transition of liquid crystals (LCs) from a planar to homeotropic state, which caused a bright-to-dark optical shift. It was proved that double-chain surfactants and the mixed surfactants inclined to adsorb at the ALI triggering the orientational transition. Inspiringly, a quicker and more sensitive dark-to-bright optical response was observed for mixed surfactant system-decorated interfaces in contact with proteins (such as bovine serum albumin (BSA), lysozyme, and trypsin) as opposed to the single surfactant systems. The ALI decorated by the 12-3-12/[C12mim]Br system was particularly efficient and exhibited the most sensitive optical response for BSA (0.01 ng mL−1). The order parameters (SCD) of surfactants tails at the interface and the free energy of proteins with 12-3-12 and [C12mim]Br were calculated, respectively. The results explain that the 12-3-12/[C12mim]Br-laden ALI shows a quicker and more sensitive optical response for BSA. This work inspired us to study mixed surfactant systems-decorated LC interfaces and further provides new insights for different chemical and biological applications.

A methodology for chemical formulation for wettability alteration induced water imbibition in carbonate reservoirs

Oil recovery tests are performed to evaluate the performance of different single and mixed-surfactant systems. Contact angle and O/W IFT measurements are first used to derive the capillary driving forces necessary for spontaneous imbibition. Surfactant mediated imbibition in oil-wet Indiana limestone cores resulted in additional oil recoveries over brine and the extent of oil recovery was determined by the surfactant type, initial water saturation, and brine salinity. A maximum oil recovery of 47% at 50 °C was observed for the best single surfactant system while a maximum oil recovery of 27% at 90 °C was observed for the best mixed surfactant system. It was found that the highest oil recovery occurs at intermediate water saturations. The positive effect of SO42− ions on wettability alteration is also noted with an approximately 10% incremental oil recovery observed at 1% sulfate concentration. Universal recovery curves corresponding to gravity-driven imbibition process are obtained. To obtain predictive tools for oil recovery, the ultimate oil recoveries are scaled with the capillary pressure to generate a universal oil recovery curve as a function of the cloud point temperature difference as a thermodynamic descriptor.

Impact of Adsorption Layer Properties on Drainage Behavior of Microscopic Foam Films: The Case of Cationic/Nonionic Surfactant Mixtures

Aqueous mixtures of cationic hexadecyltrimethylammonium chloride (CTAC) and nonionic pentaethyleneglycol monododecyl ether (C12E5) are investigated. Adsorption layer properties are systematically studied within a wide concentration range for a 1:1 molar ratio of the surfactants. Surface tension and dilatational rheology measurements are conducted by profile analysis tensiometry. The interfacial data are juxtaposed to drainage kinetics and stability results for microscopic foam films, investigated by microinterferometric thin liquid film instrumentation. The obtained results give experimental evidence of synergistic interactions in the studied solutions, as compared to the corresponding single surfactant systems. Specific runs of dynamic and equilibrium surface tension curves are registered against the total surfactant quantity; the surface dilatational elasticities for the mixtures are systematically higher. A clear correlation is established between adsorption layer performance and foam film characteristics. The maxima of the film lifetimes are well outlined, and the respective values are shifted towards lower overall concentrations. The reported results substantiate the key role of the adsorption layers, and the surface dilatational properties in particular, for foam film drainage kinetics and stability. The well-expressed synergy observed in adsorption layer and foam film properties suggests the substantial benefits of using mixed surfactant systems in the design and fine-tuning of foam systems for innovative applications.

Exploiting self-assembled soft systems based on surfactants, biopolymers and their mixtures for inhibition of Citral degradation under harsh acidic Conditions

The chemical instability of Citral in acidic conditions is viewed as hurdle to commercialize it in food/beverage industries. We attempted to stabilize citral in various single and mixed surfactant systems at pH 1.0 and temperature 25 °C. The study highlights the importance of amount and density of positive charge of cationic surfactants and oxyethylene content of nonionic surfactants at the interface of self-assembly in inhibiting citral degradation. The hybrid of Chitosan and P123 showed a significant increase in the half-life of citral compared to that in its individual components. The results of the study suggest that it is possible to stabilize citral in strong acidic environs having a pH as low as 1.0 using mixed surfactant or polymer-amphiphile systems with significant positive charge/number of oxyethylene in their single components. Such polymer-surfactant systems formulations if biocompatible/food grade may act as promising media to enhance shelf life of citral.

Solubilization of direct dyes in single and mixed surfactant system: A comparative study

Interaction of direct dyes (Direct Orange 26 and Direct Red 9) has been investigated via spectroscopic analysis in single cationic (cetyltrimethylammonium bromide) and cationic-nonionic mixed surfactant media. The solubilization capabilities of surfactants solutions have been assessed in terms of the partition coefficient (Kx) and binding constant (Kb). Critical micelle concentration (CMC) of the surfactant, electrostatic interactions, hydrophobic associations, and polarity of the medium plays important role in the said process. Significant enhancement in the solubility of both dyes was observed on the addition of non-ionic surfactants (Triton X-100 and Tween-20) in the CTAB solution. Solubility was found to be directly related to the extent of mixed micellization. The negative values of the Gibbs energy of binding (ΔGb) and Gibbs energy of partition (ΔGp) are the predictors to prove the feasibility and spontaneity of the process. The results, herein, suggest that the use of mixed micellar media for solubilization of direct dyes is advantageous over that of a single surfactant.