Concentration Of Cationic Surfactant Research Articles

Evaluating the Extraction and Quantification of Marine Surfactants from Seawater through Solid Phase Extraction and Subsequent Colorimetric Analyses.

Surfactants are amphiphilic molecules that adsorb to interfaces and affect the interfacial tension. Surfactants in seawater can impact gas-exchange, surface properties, and the composition and fate of sea spray aerosol. The accurate quantification of surfactants and their classes is crucial to constraining the effect of surfactants in seawater and their role in air-sea exchanges. Here, we evaluate and optimize a solid phase extraction (SPE) method paired with colorimetry and UV-vis spectroscopy to quantify the concentrations of anionic, cationic, and nonionic surfactants in seawater. We compare tandem SPE with two-step SPE and different elution volumes and evaluate the impact of different interferents. Improved extraction efficiencies were obtained with an 8 mL acetonitrile elution and with separate ENVI-18 and ENVI-Carb extractions, instead of tandem. With complex surfactant mixtures, the presence of anionic surfactants interfered with the quantification of cationic surfactants and caused underestimations of up to 83%. Using a two-step extraction and analyzing each seawater SPE extract separately during colorimetric quantification help avoid the effects of interferents and ensure more representative quantification of surfactants. With this method, average seawater surfactant concentrations ranged from 0.04 to 0.06 μM. At the highest concentrations, the class composition comprised 23% anionic, 21% cationic, and 56% nonionic surfactants.

Synthesis and Kinetics of CO2-Responsive Gemini Surfactants.

Surfactants are hailed as "industrial monosodium glutamate", and are widely used as emulsifiers, demulsifiers, water treatment agents, etc., in the petroleum industry. However, due to the unidirectivity of conventional surfactants, the difficulty in demulsifying petroleum emulsions generated after emulsification with such surfactants increases sharply. Therefore, it is of great significance and application value to design and develop a novel switchable surfactant for oil exploitation. In this study, a CO2-switchable Gemini surfactant of N,N'-dimethyl-N,N'-didodecyl butylene diamine (DMDBA) was synthesized from 1, 4-dibromobutane, dodecylamine, formic acid, and formaldehyde. Then, the synthesized surfactant was structurally characterized by infrared (IR) spectroscopy, hydrogen nuclear magnetic resonance (1H NMR) spectroscopy, and electrospray ionization mass spectrometry (ESI-MS); the changes in conductivity and Zeta potential of DMDBA before and after CO2/N2 injection were also studied. The results show that DMDBA had a good CO2 response and cycle reversibility. The critical micelle concentration (CMC) of cationic surfactant obtained from DMDBA by injecting CO2 was 1.45 × 10-4 mol/L, the surface tension at CMC was 33.4 mN·m-1, and the contact angle with paraffin was less than 90°, indicating that it had a good surface activity and wettability. In addition, the kinetic law of the process of producing surfactant by injecting CO2 was studied, and it was found that the process was a second-order reaction. The influence of temperature and gas velocity on the reaction dynamics was explored. The calculated values from the equation were in good agreement with the measured values, with a correlation coefficient greater than 0.9950. The activation energy measured during the formation of surfactant was Ea = 91.16 kJ/mol.

Investigation of micellization and thermodynamic properties of cationic gemini surfactant (12-2-O-2-12) in the presence of organic solvents

The micellization behaviour and thermodynamic properties of synthesized cationic gemini surfactant (12-2-O-12-12), N,N′-didodecyl-N,N,N′,N′-tetramethyl-N,N′-(oxybis(ethane-2,1-diyl))-diammonium dibromide were studied in the presence of organic solvents for four different temperatures (25, 30, 35 and 40 °C). Aqueous solutions of 10 % and 20 % methanol (MeOH), ethanol (EtOH), isopropanol (IPOH) and dimethyl sulfoxide (DMSO) were used as solvents. The critical micelle concentration (CMC) of cationic gemini surfactant and the degree of counterion dissociation (α) were determined by the conductometric method. Using the CMC and α values for each of the four temperatures, the values of the standard Gibbs free energy (ΔGmo), Gibbs free energy of transfer (ΔGm,transo), enthalpy (ΔHmo), and entropy (ΔSmo) of micellization were calculated. It was observed that the CMC and α values increased with increasing solvent percentage and temperature. It was found that in all cases, the standard Gibbs free energy and enthalpy values were negative while both the micellization entropy and the standard Gibbs free energy of transfer are positive. Negative Gibbs free energy values indicated that micellization was a spontaneous situation, while positive entropy values indicated the existence of a disordered situation. The positive ΔGm,transo values show that the presence of solvents makes the environment unfavorable for micelle formation.

Oil-in-Water Emulsions Probed Using Fluorescence Multivariate-Curve-Resolution Spectroscopy.

Hydrophobic surfaces in contact with aqueous media are omnipresent in nature. A plethora of key biological and physiological processes occur at the interface of immiscible fluids. Besides its fundamental importance, probing such interfaces is rather challenging, especially when one medium is bathed in the other. Herein, we demonstrate a fluorescence-based method that probes the oil-water interface and interfacial processes through surface dielectric perturbations. The fluorescence response of Nile Red is measured in hexadecane in water nanoemulsions. Three major spectral components appear: two from the bulk liquid media (hexadecane and water) and a distinct band at around 640 nm due to the interfacial component. Such spectra are deconvoluted using the multivariate-curve-resolution algorithm, and interface-correlated fluorescence spectra are attained. The influence of anionic sodium dodecylbenzenesulfonate (SDBS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants on the oil-water interface is elucidated with concentration-dependent measurements. A charge-dependent spectral shift is observed. The interface correlated band at 641 nm for bare hexadecane nanoemulsions red shifts in the presence of anionic surfactants, indicating an apparent dielectric increase. In contrast, the same band gradually blue shifts with increasing cationic surfactant concentration, indicating an apparent interface dielectric decrease. Such a method can be utilized to probe alterations at interfaces beyond the oil/water interface.

Designing the structure of cationic star-shaped trimeric surfactants most active in micelle formation using molecular connectivity indices

A model expressing the relationship between the logarithm of critical micelle concentration of cationic star-shaped trimeric surfactants and topological indices was obtained using only molecular connectivity indices. Based on the obtained model, the exemplary compound most active in micelle formation was designed. The analysis of the influence of various structural factors on the value of the critical micelle concentration was supported by atomic charge studies. The obtained model will be used to design new star-shaped trimeric surfactants that are more active in formation of micelle as well as to predict their critical micelle concentration.

Comparison of dodecyl trimethyl ammonium bromide (DTAB) and cetylpyridinium chloride (CPC) as corrosion inhibitors for mild steel in sulphuric acid solution

Two essential cationic surfactants, dodecyl trimethyl ammonium bromide (DTAB) and cetyl pyridinium chloride (CPC) with differences in the alkyl chain, were investigated as corrosion inhibitors on mild steel (MS) in 0.5 M H2SO4 with weight loss (WL) and the potentiodynamic polarization (PDP) method. Three different temperatures were used to maintain the reported sample solutions (298.15, 308.15, and 318.15 K) for concentrations ranging below, above, and at the optimum critical micelle concentration (CMC) of the cationic surfactants. Results show that 0.5 M DTAB having ammonium group gave higher inhibition efficiency than 0.5 M CPC having pyridinium group by PDP method. The inhibition efficiencies were determined as 98.6% for 0.5 M DTAB and 89.38% for 0.5 M CPC after 24 h immersion at 298.15 K. The extreme inhibition efficiency depends on the chain length and decreases with an increase in temperature as well as increases with the addition of concentration of cationic surfactants. Around CMC, both surfactants CPC and DTAB showed the highest inhibition efficiency which follows the isotherm of Langmuir adsorption and illustrates a mixed type of corrosion inhibitors with the predominance of cathodic reactions. Additionally, the proposed mechanisms of inhibitors showing both physical and chemical adsorption confirmed by the free energy of adsorption (-ΔGads0) for DTAB were >28–34.5 kJ/mol and for CPC were >31.07–42.91 kJ/mol.

Enhanced electrochemical properties of cobalt oxide nanoparticle electrode modified with low concentration of cationic surfactant

Metal oxides are proficient electrode materials for supercapacitors because of their physiochemical properties, especially their wide range of oxidation states that facilitate charge transfer in redox reactions and compatibility with electrolytes. Their performances can be further improved by adding surfactants, which also help with controlled synthesis, inhibit aggregation, and alter surface characteristics. The functional groups present in the surfactant molecule can undergo chemical bonding with the surface of the metal oxide, thereby modifying their surface chemistry and electronic characteristics. Recent research has focused on increasing the specific capacitance of cobalt oxide owing to its large surface area and size. The surfactants help to control the surface modification as a size-reducing agent and improve the electrochemical properties. Herein, A facile co-precipitation method is employed in synthesising cobalt oxide without cationic surfactant cetyltrimethylammonium bromide (CTAB) and with different concentrations of CTAB, followed by calcination. Herein, we compare the electrochemical properties with varying concentrations of surfactant-assisted Co3O4. The modified Co3O4 electrode with a low surfactant concentration (CO 1) exhibits a highly specific capacitance of 531F/g at 5 mV/s with a potential window of 0.7 V. The CO 1 electrode is suitable for supercapacitor devices with a specific capacitance of 296F/g at 0.8 A/g. Moreover, the asymmetric supercapacitor composed of CO1//AC demonstrated a remarkable energy density of 46.2 Wh/Kg and a robust power density of 800 W/kg. These results indicate that the hierarchical porous structure accelerates electron and ion movement, lowers charge transfer resistance, and improves hybrid electrode capacitive properties.

Enhance electrocoagulation-flotation (ECF) removal efficiency perfluorohexanoic acid (PFHxA) by adding surfactants

This research focuses on the application of electrocoagulation-flotation (ECF) in the removal of perfluorooctanoic acid (PFHxA), a prevalent short-chain perfluoroalkyl substance in semiconductor manufacturing, especially at concentrations of industrial wastewater levels. We explored the effectiveness of ECF, which employs sacrificial electrodes to create metal ions and bubbles for pollution extraction. The study particularly examines the role of various surfactants in augmenting PFHxA removal. We observed that at an initial PFHxA concentration of 1 mM, both anionic and cationic surfactants modestly increased removal efficiency, with limited impact from electrostatic repulsion. Significantly, at a higher concentration of 5.0 mM, cationic surfactants, notably DTAB with its short carbon chain, markedly enhanced PFHxA elimination. The superior performance of DTAB is attributed to its facilitation in Al(OH)3 crystal formation, promoting PFHxA adsorption, efficient micelle or bubble formation with PFHxA, and the stability of resulting flocs. Our findings underscore the efficacy of DTAB as a surfactant in ECF for high-concentration PFHxA scenarios, emphasizing the importance of surfactant and electrode material selection in optimizing PFAS treatment in wastewater systems. This study contributes valuable insights into refining PFAS remediation strategies in real industrial wastewater applications.

Polydiacetylene/Zn2+/ZnO nanocomposites for colorimetric detection of cationic surfactants: Effects of ZnO ratios, solvents, and stimuli structures

Polydiacetylenes (PDAs) are smart materials that have been utilized as colorimetric sensors of various stimuli. Fine-tuning the sensitivity of PDAs often requires structural modification of their side chains and/or headgroups, involving complicated synthesizing and time-consuming purifying processes. This contribution presents a simple approach for controlling the sensitivity of PDA/Zn2+/ZnO nanocomposites to cationic surfactants. We have found that the detection of cationic surfactants in different concentration regions can be achieved by varying the ZnO ratios and the alkyl chain lengths of PDAs. The nanocomposites with higher ZnO ratios or longer alkyl side chains exhibit the color transition at higher concentrations of cationic surfactants. The nanocomposites can also detect the cationic surfactants in different organic solvents and buffer solutions. Moreover, the sensors can be used to differentiate the structures of cationic surfactants. The cationic surfactants with shorter alkyl chains result in the color transition at higher concentrations. The number of alkyl chains and headgroups in cationic surfactants also affects the color-transition behaviors. Our results extend the utilization of PDA materials with tunable sensitivity for sensing the cationic surfactants in various media.

Stability of the emulsion during the injection of anionic and cationic surfactants in the presence of various salts

Smart water injection is one of the engineering techniques to enhance oil recovery (EOR) from carbonate and sandstone reservoirs that have been widely used in recent decades. Wettability alteration and IFT are among the essential and influential mechanisms that can be mentioned to achieve EOR. One of the critical issues in the field of EOR is the effect of reservoir ions on the formation and stability of the emulsion. Investigating the role and performance of these ions during EOR processes is of significant importance. These processes are based on smart water injection and natural production. In this research, stability was investigated and formed during the injection of different concentrations of anionic and cationic surfactants, respectively alpha olefin sulfonate (AOS) and cetrimonium bromide (CTAB), into a water–oil emulsion with a volume ratio of 30–70. Considering the droplet diameter distribution and the flow speed of separation by centrifugation, the optimal concentration level has been investigated in both surfactants. Based on the results, the highest stability and emulsion formation occurred in the presence of AOS surfactant. Then different concentrations of CaCl2, MgCl2, and NaCl salts were added in optimal concentrations of both surfactants. The formation and stability of the emulsion was checked by examining the distribution of the droplet diameter and the separation flow rate. AOS anionic surfactant had the most stability in the presence of MgCl2 salt, and better performance in stability of the emulsion was obtained. The maximum number of droplet diameters in the optimal concentration for AOS and CTAB surfactant systems is 1010 and 880, respectively, and for binary systems of AOS surfactant and MgCl2, CaCl2 and NaCl salts, it is 2200, 1120 and 1110, respectively. Furthermore, for the CTAB binary system in the presence of MgCl2, CaCl2, and NaCl salts, it is 1200, 1110, and 1100, respectively. The stability of the emulsion of salts in the presence of both AOS and CTAB surfactants was MgCl2 > CaCl2 > NaCl.

Effect of Surfactants on Reverse Osmosis Membrane Performance

The aim of this study was to evaluate the performance of a reverse osmosis (RO) membrane in surfactant removal using various surfactant model aqueous solutions. The separation tests were performed with laboratory scale units in a dead-end configuration. Cellulose Acetate (CA) and Polyamide (PA) RO membranes were used with nonionic, anionic, or cationic surfactants at a wide range of concentrations. Membrane performance was evaluated using permeate flux and total organic carbon (TOC) rejection. The effects of surfactant type and concentration on RO membranes were assessed. Permeate flux of the PA membrane depended on the surfactant type and concentration. The separation of cationic surfactant aqueous solutions yielded the lowest permeate flux, followed by nonionic and anionic surfactant aqueous solutions, respectively. Surfactant adsorption on the membrane surface occurred at very low concentration of cationic and nonionic surfactants due to electrostatic and hydrophobic interactions, respectively, which affected permeate flux, and micelles did not affect the permeate flux of PA membrane. However, for CA membrane the permeate flux was not affected by the feed solution. Both membranes exhibited satisfactory TOC rejection (92–99%). This study highlights the importance of assessing interactions between membrane material and surfactant molecules to mitigate membrane fouling and guarantee a better performance of the RO membrane.

Capsaicin-loaded alginate nanoparticles embedded polycaprolactone-chitosan nanofibers as a controlled drug delivery nanoplatform for anticancer activity

Nanocarrier-based drug delivery systems have been designed into various structures that can effectively prevent cancer progression and improve the therapeutic cancer index. However, most of these delivery systems are designed to be simple nanostructures with several limitations, including low stability and burst drug release features. A nano-in-nano delivery technique is explored to address the aforementioned concerns. Accordingly, this study investigated the release behavior of a novel nanoparticles-in-nanofibers delivery system composed of capsaicin-loaded alginate nanoparticles embedded in polycaprolactone-chitosan nanofiber mats. First, alginate nanoparticles were prepared with different concentrations of cationic gemini surfactant and using nanoemulsion templates. The optimized formulation of alginate nanoparticles was utilized for loading capsaicin and exhibited a diameter of 19.42 ± 1.8 nm and encapsulation efficiency of 98.7 % ± 0.6 %. Likewise, blend polycaprolactone-chitosan nanofibers were prepared with different blend ratios of their solutions (i.e., 100:0, 80:20, 60:40) by electrospinning method. After the characterization of electrospun mats, the optimal nanofibers were employed for embedding capsaicin-loaded alginate nanoparticles. Our findings revealed that embedding capsaicin-loaded alginate nanoparticles in polycaprolactone-chitosan nanofibers, prolonged capsaicin release from 120 h to more than 500 h. Furthermore, the results of in vitro analysis demonstrated that the designed nanoplatform could effectively inhibit the proliferation of MCF-7 human breast cells while being nontoxic to human dermal fibroblasts (HDF). Collectively, the prepared nanocomposite drug delivery platform might be promising for the long-term and controlled release of capsaicin for the prevention and treatment of cancer.

Experimental investigation of the controversial effects of a cationic surfactant with brine on spontaneous imbibition of an asphaltenic crude oil

Carbonate formations, which are often naturally fractured and oil-wet, include a significant portion of the discovered oil reserves. Due to their tendency to retain oil at the rock surface, enhanced oil recovery (EOR) from these reservoirs is difficult. It has been suggested that low salinity (LS) water injection be used to recover more oil from these types of oil reservoirs. A surfactant is one of the chemicals that is broadly applied as an agent to alter wettability towards water-wet conditions. In these reservoirs, if the wettability of the reservoir rock is altered from mostly oil-wet to mostly water-wet, recovery efficiency can be greatly enhanced.In this study, the synergistic effect of a modified brine solution (i.e., increasing the concentration of (SO42-)) and a cationic surfactant, namely cetyltrimethylammonium bromide (CTAB) with two different concentrations (100 ppm and 300 ppm) on the wettability of dolomite rock was considered. The contact angle is used to assess wettability alteration from dolomite rock surface. Also, oil recovery was tested in dolomite core samples via spontaneous imbibition procedures at 60 °C for 30 days. Using the modified brine, the contact angle was reduced from 130° to 27°, and the oil recovery increased from 0% to 33%. While CTAB-surfactant decreased the contact angle from 140° to 32° and 120° to 34°, respectively, for concentrations of 300 ppm and 100 ppm. Moreover, oil recovery was increased to 7.95% and 6.60 % and at concentrations of 300 ppm and 100 ppm, respectively. The oil-wet dolomite rock wettability can be modified by using the sulfonate ion and a cationic surfactant. Indeed, by absorbing SO42- ions on the dolomite slice surface, a repulsive force is formed between SO42- and the carboxylate on its surface and the wettability changes from an oil-wet to a water-wet condition. Furthermore, electrostatic interactions between the surfactant's positively charged head and the negatively charged carboxylate cause the cationic surfactant to adsorb on the oil-wet surface. Indeed, the wettability changes to the water-wet condition when the carboxylate group is removed from the rock surface by forming an ion pair. On the other hand, for low oil recovery in surfactant imbibition, three different scenarios were considered, namely: I) reduction of cationic surfactant concentration in the Amott cell, II) oil snap-off phenomenon, and III) asphaltene deposition and plugging of the pores. The results of the three proposed scenarios are as follows: I) when re-imbibing cationic surfactant into the dolomite core surface, shifting the wettability state from oil-wet to water-wet resulted in higher oil recovery (scenario result (I)), II) after CTAB flooding into the micromodel with varied pore throats, oil could be released from the porous medium throats and the walls of pores. As a result, an increase in oil recovery was seen (scenario result (II)), and III) an oil-in-water emulsion was formed as a result of the interactions between asphaltene and the cationic surfactant, and asphaltene became more unstable. As a result, asphaltene is deposited on the rock surface, plugging pores and reducing permeability, resulting in a decrease in oil recovery (scenario result (III)). The findings of this study can help for better understanding of the impact of modified bine water and cationic surfactant on dolomite rock and the interaction between asphaltene and cationic surfactant and their impact on ultimate oil recovery.

Strategies for the evaluation of the eye irritation potential of different types of surfactants and silicones used in cosmetic products

The ocular irritation potential of products that may come into contact with the eyes should be assessed by the combination of different in vitro alternative methods to determine different mechanisms of toxicity previously evaluated by the Draize in vivo assay. Thus, this study proposed to apply two strategies for the prediction of the eye irritation potential of different concentrations of surfactants and silicones, the first one involving evaluation Hen's Egg Test – Chorioallantoic Membrane (HET-CAM), and the other one using Bovine Corneal Opacity and Permeability (BCOP) followed by histopathological. HET-CAM was considered important in assessing the ocular irritation potential and, despite classifying almost all surfactants as “severe irritants”, it could discriminate moderate and slight irritant SLES concentrations as well as Cocoamidopropyl Betaine as a severe irritant, when the coagulation score was taken into consideration. The BCOP assay alone also did not offer a good prediction of the irritant potential of surfactants, since almost all of them were classified as “no prediction can be made”. However, the histopathological evaluation of the BCOP corneas was very important for establishing the degree and depth of damage related to reversibility. The present study also showed those strategies are sensitive to small variations in the studied anionic, cationic amphoteric surfactant concentrations and can be used for predicting their toxicity in the final product and can be used depending on the focus of the analysis.

Application of an experimental design methodology for the optimization of cosmetotextile impregnation process by β-cyclodextrin based microcapsules

Neroline-loaded microcapsules based on β-cyclodextrin polyurethane material were fixed on cotton fabric using an impregnation technique. The process parameters were optimized so as to achieve a maximum microcapsules deposition and binding. Simultaneous evaluation and optimization of the effects of interdependent parameters was achieved using an experimental design based on response surface methodology. The selection of the mathematical model and its use for statistical analysis were done by the least squares method using the Minitab 19 software. The optimal impregnation conditions yielding a fabric mass gain of 8.56% are as follow: 21 g·L−1 for the microcapsules concentration, 31 g·L−1 for the polyurethane cross-linker concentration and 0.72 g·L−1 for the cationic surfactant concentration. The morphological and mechanical characterization, and air permeability evaluations of the resulting cosmetotextile fabric show the suitability of the process in terms of applicability and end-use properties.

Experimental research on synergistic drag reduction of cationic surfactant and nonionic polymer

The coupling of surfactant and polymer can weaken their shortcomings, improve drag reduction rate, and enhance the stability of drag reduction. This paper takes the cationic surfactant octadecyl trimethyl ammonium chloride and the nonionic polymer polyethylene oxide as the research objects, and uses the coaxial cylinder system of Anton Paar MCR102 to study the synergistic drag reduction of cationic surfactant and nonionic polymer. The experimental results show that cationic surfactants and nonionic polymers has obvious synergistic drag reduction. Compared with 800 ppm OTAC/NaSal solution or 40 ppm PEO solution, the drag reduction increases by 61.49% and 19.78%, respectively. Moreover, the drag reduction rate of the mixed solution is not monotonically increasing with the surfactant concentration. When the OTAC/NaSal concentration reaches polymer saturation point of 1200 ppm, the drag reduction rate of the mixed solution reaches the maximum value of 14.09% and the drag reduction rate increases by 34.15%; when the concentration of OTAC/NaSal is less than 1200 ppm, the drag reduction rate increases with the increase of the concentration of cationic surfactant; however, when the concentration of OTAC/NaSal is greater than 1200 ppm, the drag reduction rate is basically stable. In addition, the shear resistance of the mixed solution is significantly enhanced.

Concentration and carbon chain length effects of cationic surfactant in enzymatic production of cellulose nanostructures

This work evaluated the effect of cationic surfactants [cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TDTAB), and dodecyltrimethylammonium bromide (DTAB)], and its concentration (0.03, 0.30, and 3.00 mM) on the production by enzymatic hydrolysis and surface modification of cellulose nanostructures (CNSs), from the one-step method. From FTIR spectra, changes and surfactant peaks and bands for modified CNSs compared to CNS were observed. For XRD results, the crystalline structure was more altered for CTAB and TDTAB, especially for higher concentrations, not changing cellulose’s crystalline structure. The surfactants affected colloidal stability, which CTAB promoted a higher shielding effect than DTAB and TDTAB, reducing the negative charges present in nanocellulose, while high concentrations lead to saturation of colloidal system, creating micelles and causing agglomerates. However, CNS CTAB showed smaller particle sizes for lower concentrations (90–100 nm), lower sugar production (50 µg g−1) for high concentrations, and cellulose nanocrystals obtaining. CNS DTAB and CNS TDTAB did not present statistical differences for particle size. Thermal stability was also affected. CNS DTAB presented the highest Tonset (250–254 °C) compared to CNS TDTAB and CNS CTAB. Thus, these results prove and suggest the possible application of these modified CNSs to develop nanocomposites with excellent dispersion, resulting in promising properties.

Photophysical characterization of a sub-micellar triblock copolymer-cationic surfactant aggregate for nanostructure synthesis

Surfactant assemblies are popular media for the synthesis of a variety of nanostructures. However, the use of excessive surfactants in these assemblies is detrimental to biological and medical applications. Herein, we optimized the size and interfacial packing of a sub-micellar aggregate of a triblock copolymer F127 (poly-(ethylene oxide)101 (EO101)−poly(propylene oxide)56 (PPO56)−PEO101), and several cationic alkyl trimethylammonium surfactants at minute concentrations and demonstrated its feasibility in synthesizing gold nano-triangles. We tracked various stages of the sub-micellar aggregate using an ultrasensitive photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS or Pyranine). The emission intensity (protonated/deprotonated) ratio of HPTS follows an intricate pattern against the surfactant concentration displaying three transition points (T1–3). The ratio starts to increase above an initial concentration (T1), attaining a maximum at an intermediate concentration (T2), and after that, decreases again before leveling off at a higher concentration (T3). Fluorescence anisotropy measurements of the methoxy analog 8-methoxypyrene-1,3,6-trisulfonate (MPTS) further revealed that the most organized state is near the critical point T2. Moreover, isothermal titration calorimetry (ITC) showed maximum enthalpy change at the same composition confirming optimum interaction. Finally, we show that the assemblies containing ultralow concentrations of both F127 and cationic surfactant can be a potent medium for synthesizing gold nano-triangles.

Urea induces (unexpected) formation of lamellar gel-phase in low concentration of cationic surfactants

HypothesisThe unexpected formation of a lamellar structure with concomitant gelation in solutions containing high urea concentration (40 wt%) and relatively low amount of cationic surfactant (3 wt%), indicates that a hierarchically structured complex is formed by both molecules. ExperimentsGels formed by combination of aqueous solutions of urea and C12TAB, C14TAB or C16TAB were prepared in different proportions and their structures at microscopic and mesoscopic levels were investigated using XRD and SAXS, respectively. The elastic and viscous moduli and yield stress of the samples were determined and correlated with the composition and structuration of the gels. The lamellar structure is reversibly thermically destroyed and this process was investigated using DSC. FindingsXRD revealed that, at microscopic scale, the gels are formed through crystallization of adducts containing surfactant molecules loaded into the cavities of honeycomb-like urea assemblies. Such crystalline phase arranges itself in lamellae with interplanar distance around ∼20–30 nm, which were observed by SAXS. This hierarchical structure is independent of the chain length of the cationic surfactants. The blocks of lamellae dispersed in the continuous phase form a three-dimensional rigid particulate network structure, giving the characteristic rheological behavior of a hydrogel. DSC revealed a reversible thermal transition at around 20–25 °C, beyond which the adducts and the lamellar phase are destroyed and micelles are formed. The characteristic transition temperature is independent of the chain length of the surfactant, and thus, it is not associated with their Krafft temperatures. The structures of the gels indicate that they resemble alpha-gels formed by fatty-alcohols and surfactants, although they self-assemble by different driving forces.

Membrane technology for the treatment of industrial wastewater containing cationic surfactants

The composition of industrial wastewater, its purification and concentration processes using ceramic membrane modules were investigated. Industrial wastewater produced as a result of washing the production line at a plant manufacturing cationic surfactants (in the esterquats group) was subjected to membrane filtration in a semi-pilot plant, run in concentration mode. Analysis of the raw wastewater showed very high organic matter content, expressed as COD, in the range of 17,700 to 24,300 mg L−1 and the concentration of cationic surfactants amounted to 2890–3390 mg L−1 mg/L. Ceramic membrane modules with a pore size of 0.14 μm exhibited high effectiveness in surfactant wastewater treatment. COD, TOC and turbidity were reduced by 93%, 95%, and 99%, respectively. When the process was run in concentration mode almost 50% of the permeate was recovered.