Anionic Sodium Dodecyl Sulfate Research Articles

Deciphering the Kinetic Study of Sodium Dodecyl Sulfate on Ag Nanoparticle Synthesis Using Cassia siamea Flower Extract as a Reducing Agent.

Silver nanoparticles (Ag NPs) were synthesized using Cassia siamea flower petal extract (CSFE) as a reducing agent for the first time. In its presence and absence, the correlative effects of the anionic surface-active agent sodium dodecyl sulfate (SDS) were studied with respect to the development and texture of Ag NPs. Under different reagent compositions, the Ag NPs were inferred by localized surface plasmon resonance peaks between 419 and 455 nm. In the absence of SDS, there was a small eminence at 290 and around 350 nm, pointing toward the possibility of irregular polytope Ag NPs, which was confirmed in the transmission electron microscopy images. This elevation vanished beyond the cmc of [SDS], resulting in spherical and oval shaped Ag NPs. The effects of reagent concentrations were studied at 25 °C and around 7 and 9 pH in the absence and presence of SDS, respectively. Also, kinetic studies were performed by UV–visible spectrophotometry. Prodigious effects on shape and size were found under different synthesis conditions in terms of hexagonal, rod-, irregular-, and spherical shaped Ag NPs. Furthermore, the antimycotic activity of the synthesized Ag NPs was established on different Candida strains, and best results were found pertaining Candida tropicalis. The ensuing study impels the control of texture and dispersity for Ag NPs by CSFE and SDS, and the resultant polytope Ag NPs could be a future solution for drug-resistant pathogenic fungi.

Modifications in the nanoparticle-protein interactions for tuning the protein adsorption and controlling the stability of complexes

We report the pathways to suppress or enhance the protein adsorption on nanoparticles and thereby control the stability of the nanoparticle-protein complexes with the help of selective additives. This has been achieved by tuning the electrostatic interaction between the nanoparticles and proteins, in the presence of surfactant and multivalent counterions. The preferential binding of the proteins with the surfactant and multivalent ions induced charge reversibility of nanoparticles can lead to adsorption of an otherwise non-adsorbing protein and vice versa. The findings are demonstrated for anionic silica nanoparticles and two globular proteins [lysozyme (cationic) and bovine serum albumin (BSA) (anionic)] as model systems, in the presence of two ionic surfactants [anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB)], and ZrCl4 as multivalent salt. Small-angle neutron scattering with the unique advantage of contrast variation has been used to probe the role of individual components in the multi-component system. It is shown that the non-adsorbing behavior of BSA with silica nanoparticles changes into adsorbing in the presence of oppositely charged DTAB surfactant, whereas the strong adsorbing behavior of lysozyme on nanoparticles modifies to be non-adsorbing in the presence of oppositely charged SDS surfactant. The presence of multivalent counterions (ZrCl4) leads the charge reversal of the nanoparticles, transforming the lysozyme from adsorbing to non-adsorbing, and no significant change in the behavior of BSA. The results presented can find potential applications in the field of nanobiotechnology.

Unusual Maximum in the Adsorption of Aqueous Surfactant Mixtures: Neutron Reflectometry of Mixtures of Zwitterionic and Ionic Surfactants at the Silica-Aqueous Interface.

The adsorption of two zwitterionic surfactants, dodecyldimethylammonium propanesulfonate (C12PS) and dodecyldimethylammonium carboxybetaine (C12CB), and of their mixtures with the cationic dodecyltrimethylammonium bromide (C12TAB) and the anionic sodium dodecylsulfate (SDS) at the silica-water interface has been studied by neutron reflection (NR). The total adsorption, the composition of the adsorbed layer, and some structural information have been obtained over a range of concentrations from below the critical micelle concentration (CMC) to about 30× the mixed CMC. The adsorption behavior has been considered in relation to the previously measured micellar equilibrium of these mixtures in their bulk solutions and their adsorption at the air-water interface. C12CB adsorbs cooperatively close to its CMC to form an almost complete bilayer on its own, whereas C12PS adsorbs more weakly in a fragmented bilayer structure. Although SDS does not normally adsorb at the silica-water interface, SDS adsorbs strongly and cooperatively with C12PS at fractional SDS compositions up to about 0.5. This cooperativity is lost when the adsorbed fraction of SDS rises above about 0.5. At this point, adsorption drops sharply, creating an unusual maximum in the variation of adsorption with a total concentration above the mixed CMC. Neither the increase in cooperativity nor the subsequent decline in adsorption results directly from variations of the independently determined monomer concentrations in the bulk solution. The adsorption maximum is predominantly the effect of strong cooperative interaction, possibly accompanied by partial segregation of SDS within the layer, followed by charge repulsion from the surface. Although the solution aggregation and adsorption at the A-W interface are similar for SDS with C12CB, the addition of SDS to C12CB at the silica-water interface promotes the opposite behavior to that of SDS with C12PS, and SDS simply disrupts the cooperative binding of C12CB. Unlike SDS, the cationic surfactant C12TAB adsorbs on silica. It therefore coadsorbs at the SiO2-W interface with either C12CB or C12PS. However, in neither case is there any pronounced cooperativity and, even though the presence of C12TAB might be expected to favor adsorption, the adsorption is generally unexpectedly low.

Highly-loaded protein nanocarriers prepared by Flash NanoPrecipitation with hydrophobic ion pairing

The efficient encapsulation of therapeutic proteins into delivery vehicles, particularly without loss of function, remains a significant research hurdle. Typical liposomal formulations achieve drug loadings on the order of 3–5% and encapsulation efficiencies around 50%. We demonstrate the encapsulation of model proteins with isoelectric points above and below pH 7 into nanocarriers (NCs) with protein loadings as high as 46% and encapsulation efficiencies above 95%. This is done by combining the continuous nanofabrication process Flash NanoPrecipitation (FNP) with the technique of hydrophobic ion pairing by forming and encapsulating an ionic complex within a nanocarrier stabilized by a block copolymer surface layer.We complex and encapsulate lysozyme with two anionic hydrophobic counterions, sodium oleate and sodium dodecyl sulfate, using either a pre-formed complex or in situ pairing. The strategy successfully forms NCs ~150 nm in diameter and achieves encapsulation efficiencies over 95%. Protein release rate from the NCs in physiological conditions and the bioactivity of released lysozyme are measured, and both are found to vary with the complexing counterion and the protein/counterion ratio used during formulation. Protein release on the time scale of weeks is observed, and up to 100% bioactivity is measured from released lysozyme.16 quaternary ammonium cationic counterions are tested to encapsulate ovalbumin in 32 formulations. Of these, 19 successfully form ~150 nm NCs with loadings up to 29% and encapsulation efficiencies up to 88%. We divide the formulations into four regimes and identify chemical factors responsible for the success or failure of a given counterion to formulate NCs with the desirable size, loading, and encapsulation efficiency. A successful ovalbumin NC formulation was then tested in vivo in a mouse nasal vaccine model and found to induce a higher titer of OVA-specific IgG than unencapsulated ovalbumin.Taken together, these findings suggest that Flash NanoPrecipitation with hydrophobic ion pairing is an attractive platform for encapsulating high molecular weight proteins into NCs. In particular, the ability to tune protein release rate by varying the counterion or protein/counterion ratio used during formulation is a useful feature.

Enhanced energy density of polyaniline nanostructured polymer nanocomposites at low electric field

This work exhibits anionic sodium dodecyl sulfate (SDS), nonionic triblock copolymer F127, and polyaniline (PANI) nanostructures. The nanorod shaped PANI-SDS-F127 1:1 demonstrates noteworthy features—scalable and extended electrical characteristics, dielectric response, and significance in high-density energy storage devices. High-frequency measurements (1 MHz–1 GHz) preserve dielectric relaxation, which is attributed to excellent charge polarization. Uniformly distributed PANI nanorods align with the induced electric field and develop high current density (J ∼ 5.270 × 105 mA m–2), electric displacement (Dmax ∼ 7.408 × 105 C m–2), and lower impedance (Zs ∼ 3.28 Ω), which result in an improved charge polarization leading to increased capacitance (Cs ∼ 6.21 μF). These properties yield notable energy density (Ue ∼ 1.08 J cm–3) and signify a polymer matrix viable to high-density energy storage capacitor devices that would be actively favorable in developing efficient electronic and electrical devices.

Disaggregation of amyloid-like protein aggregates isolated from human cataract lens

Crystallins, which represents the major lens protein, play a significant role in ensuring the lens transparency and maintenance of appropriate refractive index of the lens that help in accurate focusing of incident visible light precisely on retina to create clear image perception. Aggregation of lens proteins is known to form the basis of cataract formation. The present study is an attempt to examine the stability of the lens protein aggregates, isolated from human cataract eye lens, against an anionic detergent Sodium dodecyl sulphate (SDS), which is known to disrupt the hydrophobic interaction of protein aggregates. Data that emerged from Congo red (CR), thioflavin T (ThT) and 8-anilino-1-naphthalene sulfonic acid (ANS) binding assaysindicated their amyloidogenic nature. A significant reduction in the bathochromic shift of CR λmax and ThT fluorescence emission intensity were observed after treatment of the aggregated proteins with SDS. In the presence of SDS, a significant change in the number and size of the protein aggregates were observed during their morphological analyses under transmission electron microscopy (TEM). Based on the above data it became evident that the hydrophobic interaction plays a crucial role in formation and stabilizing the protein aggregates during cataract formation.

Interaction of a bovine serum albumin (BSA) protein with mixed anionic-cationic surfactants and the resultant structure.

The interaction of a bovine serum albumin (BSA) protein with the mixture of anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) has been investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). Both SDS and DTAB as individuals interact electrostatically as well as hydrophobically with BSA and form connected protein-decorated micelle like complexes in the aqueous solution, in which the well-defined surfactant micelles are organized along the randomly distributed unfolded polypeptide chain of the protein. The protein-surfactant interaction has been tuned by adding different molar mixtures of SDS and DTAB in BSA aqueous solution. It is found that a lower molar fraction of either surfactant in the protein-mixed surfactant complexes results in the formation of a connected protein-decorated micelle structure similar to those of pure surfactants. As the molar fraction of one of the surfactants in the mixture approaches the equimolar fraction, the structure formed by the protein-mixed surfactant is very different from the connected protein-decorated micelle like structure. Different microstructures of BSA-mixed surfactant complexes are formed, mostly governed by the structure of mixed surfactants arising from the strong electrostatic interaction of oppositely charged components. In this case, unfolded proteins wrap the structures of mixed surfactants around their surface. Along with the connected protein-decorated micelle like structure, rod-like and bilayer vesicles of protein-surfactant complexes are formed at different molar fractions of mixed surfactants.

Antiwear nano-lubricants of calcium-doped zinc oxide: Applicable to tribological activities

The tribological properties of zinc oxide (ZnO) and 12% calcium doped zinc oxide nanoparticles (ZCOs) have been investigated by performing standard tests, ASTM D4172 and D5183on a four-ball tester. All the nanoparticles were synthesized through auto combustion method. Calcium doped zinc oxide nanoparticles of different size were prepared by varying the calcination temperature as 600 °C (ZCO-1) and 1000 °C (ZCO-2) respectively. The synthesized nanoparticles have been characterized by different techniques such as powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX). Incorporation of calcium as a dopant was found to enhance the antiwear and antifriction behavior of the ZnO nanoparticles. The nanoparticles ZCO-1 with smaller size, 25 nm provided much better results as compared to ZCO-2, 35 nm. Furthermore, a stable suspension of the synthesized nanoparticles was prepared with an anionic sodium dodecylsulphate surfactant (0.25% w/v with 0.1% SDS) which increased substantially the antiwear properties and reduced simultaneously the friction between moving metal surfaces. Thus, the enhanced tribological properties may result in the commercial deployment of these nano-lubricants in lubrication industries.

Biocompatiblibility analysis of the decellularized bovine pericardium

The decellularized bovine pericardium and its potential use as a natural scaffold is a promising approach in the field of tissue engineering and regenerative medicine. The reaction of the host toward decellularized scaffolds depends on their biocompatibility, which should be satisfied being before applied in clinical use. Purpose: to evaluate the biocompatibility of the extracellular matrices, which were decellularized by trypsin enzyme and anionic sodium dodecyl sulfate (SDS) detergent. Material and methods. Pericardial sacs were acquired from 12-18 months’ age bulls. Tissue decellularization was performed by using 0.25 % Trypsin solution and 1 % ionic SDS for group I and 0.1 % SDS for group II samples. The implantation was performed on Wistar rats. The tissue samples were stained with hematoxylin & eosin, Congo red and Masson's Trichrome for histological analysis. Results. In group 1 in 3 months after subcutaneous implantation in rats we noticed the inflammation in surrounding tissue and degradation of the implant. Under the same conditions in animals of group 2 implant replacement with growing immature connective tissue was noted. Bio-implant of this group did not degrade, moreover it's integrated to the tissues of experimental rats. Conclusion. Our results showed that decellularized bovine pericardium by 0.1 % SDS can become an alternative material for tissue engineering and has the potential for further use in human surgery.

2-Hydroxy-1, 4-napthoquinone solubilization, thermodynamics and adsorption kinetics with surfactant

• Lawsone-surfactant interactions established for the first time. • Lawsone deposited on the surface of glass with silver ions, CTAB in alkaline media. • Dye adsorption kinetics discussed with various adsorptions kinetic models. • Our findings would be helpful to enhance color fastness of dye in textile processes. 2-Hydroxy-1, 4-napthoquinone (lawsone) natural red–orange dye was extracted from fresh henna (Lawsonia inermis) leaves in an alkaline media. The lawsone-surfactant solubilization constants ( K LS ) were calculated for the first time by using cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS). The standard free energy, concentration of solubilized lawsone and number of lawsone molecules solubilized into micelles were calculated and discussed. Surface excess, minimum surface area per molecule, surface pressure, free energy (adsorption and aggregation) and equilibrium constants of different states were determined from tensiometry. Different metal ions (Ag + , Co 2+ , Cu 2+ , Ni 2+ , Fe 3+ , Zn 2+ and Al 3+ ) were used to determine the complex forming ability with lawsone. Out of these, Ag + ions have strong binding capacity with lawsone. The adsorption of lawsone on the surface of glass with silver ions in presence of CTAB was also observed at pH ≥ 9.0. The pseudo-first, second-order kinetic equation, intraparticles diffusion and Elovich models were used to determine the kinetics of lawsone adsorption onto the surface of glass and a probable mechanism has been discussed. Lawsone adsorption followed second-order kinetic equation ( k 2 = 0.019 g·mg −1 ·min −1 ).

What happens when pesticides are solubilised in binary ionic/zwitterionic-nonionic mixed micelles?

HypothesisSurfactants have been widely used as adjuvants in agri-sprays to enhance the solubility of pesticides in foliar spray deposits and their mobility through leaf cuticles. Previously, we have characterised pesticide solubilisation in nonionic surfactant micelles, but what happens when pesticides become solubilised in anionic, cationic and zwitterionic and their mixtures with nonionic surfactants remain poorly characterised. ExperimentsTo facilitate characterisations by SANS and NMR, we used nonionic surfactant hexaethylene glycol monododecyl ether (C12E6), anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecylphosphocholine (C12PC) as model adjuvant systems to solubilise 3 pesticides, Cyprodinil (CP), Azoxystrobin (AZ) and Difenoconazole (DF), representing different structural features. The investigation focused on the influence of solubilisates in driving changes to the micellar nanostructures in the absence or presence of electrolytes. NMR and NOESY were applied to investigate the solubility and location of each pesticide in the micelles. SANS was used to reveal subtle changes to the micellar structures due to pesticide solubilisation with and without electrolytes. FindingsUnlike nonionic surfactants, the ionic and zwitterionic surfactant micellar structures remain unchanged upon pesticide solubilisation. Electrolytes slightly elongate the ionic surfactant micelles but have no effect on nonionic and zwitterionic surfactants. Pesticide solubilisation could alter the structures of the binary mixtures of ionic/zwitterionic and ionic/nonionic micelles by causing elongation, shell shrinkage and dehydration, with the exact alteration being determined by the molar ratio in the mixture.

Improved antifouling performance of a polyamide composite reverse osmosis membrane by surface grafting of dialdehyde carboxymethyl cellulose (DACMC)

Antifouling properties are considered to be essential to polyamide (PA) composite reverse osmosis (RO) membranes for their industrial applications. In this work, an antifouling material, dialdehyde carboxymethyl cellulose (DACMC), was prepared by the oxidation of carboxymethyl cellulose (CMC) and then grafted onto the surface of a nascent PA RO membrane to improve its antifouling properties. The results showed that DACMC grafting could endow the membrane with improved hydrophilicity, surface smoothness and NaCl retention, while the permeability was decreased slightly after DACMC grafting. The zeta potentials of the membrane could be adjusted by changing the DACMC concentration. In addition, three typical surfactants with various charge properties, including sodium dodecyl sulfate (SDS), polyoxyethylene octylphenol ether (OP-10) and cetyltrimethylammonium bromide (CTAB), were used as feed foulants to evaluate the antifouling property of membranes. The results showed that, for the anionic SDS and nonionic OP-10 surfactants, the modified membranes with more DACMC had better antifouling performance because the membrane hydrophilicity dominated the interaction between foulants and the membrane surface. For the cationic CTAB, however, the pristine membrane showed better antifouling performance than the modified membrane with low DACMC grafting concentrations (5 and 10 g/L). This difference was attributed to the stronger electrostatic adsorption between the cationic CTAB and the modified membranes with more negative charges. The modified membrane with high DACMC grafting concentrations (20 g/L) exhibited the best antifouling performance for all the surfactants thanks to its high hydrophilicity and low negative charge. Therefore, the charge and hydrophilic properties of the RO membrane must be designed rationally to enhance the antifouling performance of the RO membrane when treating surfactant-containing wastewater.

Mechanistic pathways of cationic and anionic surfactants sorption by kaolinite in water.

Surfactants are widely used in many chemical industries and as primary components of cleaning detergents due to their specific characteristics, which in turn results in high pollution of domestic and industrial wastewaters by such substances. In this study, the mechanistic pathways of the adsorption of cationic benzyl-dimethyl-dodecyl ammonium bromide (BDDAB) and anionic sodium dodecyl sulfate (SDS) surfactants on kaolinite clay in water were investigated. The results showed that the adsorption of anionic surfactant (SDS) on kaolinite is better compared with cationic surfactant (BDDAB), wherein the ♦maximum adsorption capacity was found 161.4μmolg-1 and 234μmolg-1 for BDDAB and SDS, respectively. Adsorption kinetics were the best suited to pseudo-second-order model for both BDDAB and SDS with an adsorption rate constant of 0.028gμmol-1min-1 and 0.023gμmol-1min-1, respectively. Meanwhile, the adsorption of BDDAB by kaolinite showed that the isotherm adsorption tended to follow the Langmuir-Freundlich and Freundlich isotherm models. However, the SDS adsorption isotherm obeyed only the Langmuir-Freundlich model.

Effect of pH and surfactants on the electrokinetic properties of nanoparticles dispersions and their application to the PET fibres modification

This paper presents the effect of surfactants, pH and electrolyte (0.1 × 10−3 M KCl) on the stability of the aqueous dispersions of commercial ZnO and AgCu nanoparticles. As the surfactants cationic hexadecyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic 4-(1,1,3,3-tetramethylbutyl)phenyl polyethylene glycol (Triton X-100) at concentrations of 0.5 × 10−3, 1.0 × 10−3, and 0.1 × 10−3 M, respectively, were used. The zeta potential values, z-average hydrodynamic diameter and long-term stability of ZnO and AgCu nanoparticles were examined by means of the dynamic light scattering (DLS) technique. It was found that the presence of ionic surfactants reduced the tendency of nanoparticles for agglomeration/aggregation and improved their colloidal stability. They were characterized by high (>|70| mV) and pH-independent zeta potential values. In addition, ZnO nanoparticles in the presence of ionic surfactants showed a better long-term stability than AgCu nanoparticles. Their z-average hydrodynamic diameters in CTAB and SDS were 195 ± 2 nm and 295 ± 5 nm, respectively, and remained almost unchanged for 5 days. The addition of KCl improved the stability of aqueous and containing nonionic surfactant dispersions of nanoparticles, what was reflected in the zeta potential values > 30 mV in almost the entire pH range. The stability of nanoparticles dispersion significantly affects the uniformity of nanoparticles distribution on the fibres surface. The uniformity of distribution of the ZnO and AgCu dispersion on the surface of polyester (PET) fibres was carried out by means of microscopic methods (SEM/EDS).

Electrooxidation of tetracycline antibiotic demeclocycline at unmodified boron-doped diamond electrode and its enhancement determination in surfactant-containing media

In this paper, for the first time, the study of voltammetric determination of tetracycline antibiotic demeclocycline was conducted. The oxidation of compound was investigated using a commercially available boron-doped diamond electrode pretreated electrochemically (anodic and subsequent cathodic). Addition of anionic surfactant, sodium dodecylsulfate (SDS) and cationic surfactant, cetyltrimethylammonium bromide (CTAB) to the demeclocycline-containing electrolyte solution at pH 2.0 and 9.0, respectively, was found to improve the sensitivity of the stripping voltammetric measurements. Employing square-wave stripping mode (after 30 s accumulation at open-circuit condition) in Britton-Robinson buffer, the limits of detection were found to be 1.17 μg mL−1 (2.3 × 10−6 M) for 4 × 10−4 SDS-containing buffer solution at pH 2, and 0.24 μg mL−1 (4.8 × 10−7 M) for 1 × 10−4 CTAB-containing buffer solution at pH 9.0. The feasibility of the developed approach for the quantification of demeclocycline was tested in urine samples.

Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants.

Depletion forces were measured between a silica sphere and a silica plate in solutions containing nonionic Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers and anionic sodium dodecyl sulfate (SDS) surfactants using colloidal probe atomic force microscopy. Prior research established synergistic depletion force enhancement in solutions containing SDS and unimeric Pluronic F108 block copolymers via formation of large pseudo-polyelectrolyte complexes. The current work addresses a more complex system where the polymer is above its critical micelle concentration, and surfactant binding alters not only the size and charge of the micelles but also the number of polymers per micelle. Force profiles were measured in 10 000 ppm P123 (1 wt %, corresponding to 1.72 mM based on average molar mass) solutions containing SDS at concentrations up to 64 mM and compared to micellar P123 solutions and to P123-free SDS solutions. Whereas force profiles in the SDS-free micellar P123 solutions were purely repulsive, P123/SDS complexation produced synergistic depletion force enhancement for SDS concentrations between 2 and 32 mM. The synergism that occurred within a finite SDS concentration range was explained by comparing the hydrodynamic size, molar mass, charge, and concentration of depletants in P123/SDS mixtures and their respective single-component solutions obtained with the aid of dynamic light scattering, static light scattering, and dodecyl sulfate ion-selective electrode measurements. These measurements showed that complexation produced effects that would be mutually counteracting with respect to depletion forces: decreasing the mixed micelle hydrodynamic diameter relative to SDS-free P123 micelles would tend to weaken depletion forces, while adding charge and decreasing the aggregation number of polymers per micelle (thereby increasing the number concentration of micellar depletants) would tend to strengthen depletion forces.

Pure and mixed aqueous micellar solutions of Sodium Dodecyl sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO): Role of temperature and composition

Aqueous mixtures of anionic and nonionic/cationic surfactants can form non-trivial self-assemblies in solution and exhibit macroscopic responses. Here, we investigate the micellar phase of pure and mixed aqueous solutions of Sodium Dodecyl Sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO) using a combination of Small Angle Neutron Scattering (SANS), Fourier-Transform Infrared Spectroscopy (FTIR) and rheological measurements. We examine the effect of temperature (0–60 °C), on the 20 wt% SDS micellar solutions with varying DDAO (⩽5 wt%), and seek to correlate micellar structure with zero-shear solution viscosity. SANS establishes the formation of prolate ellipsoidal micelles in aqueous solutions of pure SDS, DDAO and SDS/DDAO mixtures, whose axial ratio is found to increase upon cooling. Elongation of the ellipsoidal micelles of pure SDS is also induced by the introduction of the non-anionic DDAO, which effectively reduces the repulsive interactions between the anionic SDS head-groups. In FTIR measurements, the formation of elongated mixed ellipsoidal micelles is confirmed by the increase of ordering in the hydrocarbon chain tails and interaction between surfactant head-groups. We find that the zero-shear viscosity of the mixed surfactant solutions increases exponentially with decreasing temperature and increasing DDAO content. Significantly, a master curve for solution viscosity can be obtained in terms of micellar aspect ratio, subsuming the effects of both temperature and DDAO composition in the experimental range investigated. The intrinsic viscosity of mixed micellar solutions is significantly larger than the analytical and numerical predictions for Brownian suspensions of ellipsoidal colloids, highlighting the need to consider interactions of soft micelles under shear, especially at high concentrations.

In-situ monitoring of oil emulsion fouling in ultrafiltration via electrical impedance spectroscopy (EIS): Influence of surfactant

Some inconsistencies were found in the literature on the effect of surfactant type on membrane fouling by surfactant-stabilized oil emulsions. For instance, a recent study showed that the fouling trends revealed by optical coherence tomography (OCT) were incongruent with the flux decline trends. This study was targeted at providing more mechanistic insights on the evolution of the distinct membrane layers (namely, diffusion polarization, membrane skin and membrane microporous substrate layers) via electrical impedance spectroscopy (EIS). The three surfactants investigated were cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic Tween 20, the oil was hexadecane, and the ultrafiltration membrane was polyethersulfone (PES). The Tween 20-stabilized oil emulsions exhibited a greater flux decline than that of SDS, which agreed well with the relative shifts of the Nyquist plots and increase in conductance with time. Interestingly, the CTAB-stabilized oil emulsions exhibited a unique flux decline trend, in which the flux decline was the least in the initial 0.5 h then the worst beyond 0.75 h. Despite the negligible flux decline initially, EIS results indicated significant shifts of the Nyquist plots and increase of the conductance with time, which was tied to the extensive adsorption of CTAB. As filtration progressed beyond 0.5 h, the conductance and capacitance of the membrane skin layer in the case of CTAB-stabilized oil emulsions became respectively higher and lower than that in the case of CTAB alone, signifying that the deposition of oil emulsions had become more dominant than that of surfactants. Therefore, this study provided clear evidence that the surfactant oppositely charged to the membrane (i.e., CTAB) adsorbed extensively initially to give negligible flux decline, which was not the case for the surfactants that were similarly negatively charged like the membrane. This only lasted for 0.5 h beyond which fouling became pronounced per dictated by DLVO interaction energy.

Protein Microgel-Stabilized Pickering Liquid Crystal Emulsions Undergo Analyte-Triggered Configurational Transition.

Herein, we report a novel approach that involves Pickering stabilization of micometer-sized liquid crystal (LC) droplets with biocompatible soft materials such as a whey protein microgel (WPM) to facilitate the analysis of analyte-induced configurational transition of the LC droplets. The WPM particles were able to irreversibly adsorb at the LC-water interface, and the resulting WPM-stabilized LC droplets possessed a remarkable stability against coalescence over time. Although the LC droplets were successfully protected by a continuous network of the WPM layer, the LC-water interface was still accessible for small molecules such as sodium dodecyl sulfate (SDS) that could diffuse through the meshes of the adsorbed WPM network or through the interfacial pores and induce an LC response. This approach was exploited to investigate the dynamic range of the WPM-stabilized LC droplet response to SDS. Nevertheless, the presence of the unadsorbed WPM in the aqueous medium reduced the access of SDS molecules to the LC droplets, thus suppressing the configuration transition. An improved LC response to SDS with a lower detection limit was achieved after washing off the unadsorbed WPM. Interestingly, the LC exhibited a detection limit as low as ∼0.85 mM for SDS within the initial WPM concentration ranging from 0.005 to 0.1 wt %. Furthermore, we demonstrate that the dose-response behavior was strongly influenced by the number of droplets exposed to the aqueous analytes and the type of surfactants such as anionic SDS, cationic dodecyltrimethylammonium bromide (DTAB), and nonionic tetra(ethylene glycol)monododecyl ether (C12E4). Thus, our results address key issues associated with the quantification of aqueous analytes and provide a promising colloidal platform toward the development of new classes of biocompatible LC droplet-based optical sensors.

Synergetic Effect of Surfactant Concentration, Salinity, and Pressure on Adsorbed Methane in Shale at Low Pressure: An Experimental and Modeling Study.

The influence of an anionic surfactant, a cationic surfactant, and salinity on adsorbed methane (CH4) in shale was assessed and modeled in a series of systematically designed experiments. Two cases were investigated. In case 1, the crushed Marcellus shale samples were allowed to react with anionic sodium dodecyl sulfate (SDS) and brine. In case 2, another set of crushed Marcellus shale samples were treated with cetyltrimethylammonium bromide (CTAB) and brine. The surfactant concentration and salinity of brine were varied following the Box–Behnken experimental design. CH4 adsorption was then assessed volumetrically in the treated shale at varying pressures (1–50 bar) and a constant temperature of 30 °C using a pressure equilibrium cell. Mathematical analysis of the experimental data yielded two separate models, which expressed the amount of adsorbed CH4 as a function of SDS/CTAB concentration, salinity, and pressure. In case 1, the highest amount of adsorbed CH4 was about 1 mmol/g. Such an amount was achieved at 50 bar, provided that the SDS concentration is kept close to its critical micelle concentration (CMC), which is 0.2 wt %, and salinity is in the range of 0.1–20 ppt. However, in case 2, the maximum amount of adsorbed CH4 was just 0.3 mmol/g. This value was obtained at 50 bar and high salinity (∼75 ppt) when the CTAB concentration was above the CMC (>0.029 wt %). The findings provide researchers with insights that can help in optimizing the ratio of salinity and surfactant concentration used in shale gas fracturing fluid.