Range Of Surfactant Concentrations Research Articles

Silver nanoparticles stabilised with cationic single-chain surfactants. Structure-physical properties-biological activity relationship study

Increasing number of biological applications of silver nanoparticles requires a detailed determination of the relationship between nanoparticle structure and its physical and biological properties. In this paper, synthesis, measurements of nanoparticle size and zeta potential and some biological activities of silver nanoparticles stabilised with single-chain cationic surfactants are provided. The main goal of the study is the investigation of the relationship between molecular structure of stabilising agent, physicochemical properties and biological activity of cationic surfactant-stabilised silver nanoparticles. Two structural features, heterocyclic character of hydrophilic part of surfactant molecule and hydrophobicity change of its substituents, were correlated with synthesis, stability and biological activity of silver nanoparticles. Substituted ammonium, pyridinium and piperidinium surfactants were selected as stabilisers of silver nanoparticles. It was found that nanoparticle stabilising effect is improved by increasing the length of hydrophobic substituents on the ammonium polar head which results in the formation of nanoparticles small in size and with sufficiently positive zeta potential. Application of dibutyl-substituted ammonium surfactant molecules resulted in the formation of small silver nanoparticles in the size range 25–30 nm and a zeta potential of +60 mV. Aromatic pyridinium surfactant molecules provide slightly better stabilisation than saturated piperidinium surfactants. Surfactant-stabilised silver nanoparticles were antimicrobially efficient against Gram-positive pathogens and yeast. The highest cytotoxic activity was determined for silver nanoparticles stabilised with dibutyl-substituted ammonium surfactant and pyridinium surfactant which corresponds with small and charged nanoparticles formed by using these surfactants. Maximum cytotoxic activity was found in the surfactant concentration range 16–25 μM.

Volume expansion of erythrocytes is not the only mechanism responsible for the protection by arginine-based surfactants against hypotonic hemolysis.

A novel arginine-based cationic surfactant Nα-benzoyl-arginine dodecylamide (Bz-Arg-NHC12) was synthesized in our laboratory. In this paper we study the interaction of Bz-Arg-NHC12 with sheep and human red blood cells (SRBC and HRBC respectively) due to their different membrane physicochemical/biophysical properties. SRBC demonstrated to be slightly more resistant than HRBC to the hemolytic effect of the surfactant, being the micellar structure responsible for the hemolytic effect in both cases. Moreover, besides the hemolytic effect, a dual behavior was observed for the surfactant studied: Bz-Arg-NHC12 was also able to protect red blood cells against hypotonic lysis for HRBC in a wide range of surfactant concentrations. However, the degree of protection showed for SRBC was about 50% lower than for HBRC. In this regard, a remarkable volume expansion was evidenced only for SRBC treated with Bz-Arg-NHC12, although no correlation with the antihemolytic potency (pAH) was found. On the contrary, our surfactant showed a greater pAH when human erythrocytes were submitted to hypotonic stress, with a low volume expansion, showing a higher amount of solubilized phospholipids in the supernatant when compared with SRBC behavior. Surface plasmon resonance measurements show the molecular interaction of the surfactant with lipid bilayers from HRBC and SRBC lipids, demonstrating that in the latter neither microvesicle release or lipid extraction occurred. Our results demonstrate that the volume expansion of erythrocytes is not the only mechanism responsible for the protection by surfactants against hypotonic hemolysis: volume expansion could be compensated via microvesicle release or by the extraction of membrane components upon collisions between red blood cells and surfactant aggregates depending on the membrane composition.

Ultra-Low Interfacial Tension of a Surfactant under a Wide Range of Temperature and Salinity Conditions for Chemical Enhanced Oil Recovery

AbstractUltra-low interfacial tension (IFT) is an important parameter for selecting surfactants to apply in chemical enhanced oil recovery (CEOR). In this study, the IFT between the solution of the surfactant ANSM and Dagang crude oil was measured using the spinning drop method. The effects of the surfactant concentration, temperature, salt types and aging time on the IFT were investigated in detail. The results showed that ANSM effectively reduced the IFT without alkali. Ultra-low IFT was formed in a wide range of surfactant concentrations from 0.05∼ 0.5 wt.% and a wide range of temperatures from 20∼80°C. In addition, ANSM also showed great NaCl tolerance, with a maximum NaCl concentration of 130000 mg · L−1. Furthermore, 0.1 wt.% ANSM maintained an ultra-low IFT, even with 900 mg · L−1 CaCl2 or 1300 mg · L−1 MgCl2, in the presence of 10000 mg · L−1 NaCl. ANSM also had an excellent stability; the solution maintained the ultra-low IFT for 60 days at 90°C. Thus, ANSM proved itself as a potential candidate for CEOR.

A theoretical investigation of the influence of the second critical micelle concentration on the solubilization capacity of surfactant micelles

The solubilization of hydrophobic components by surfactants that form microemulsion droplets has been investigated from a theoretical point of view. By means of combining thermodynamics of self-assembly to form small systems with bending elasticity theory, we have been able to demonstrate a strong correlation between the second critical micelle concentration (CMC2) of surfactant micelles and their solubilization capacity (σ). The correlation may be rationalized as a consequence of all three bending elasticity constants spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant (k¯c) showing similar trends with respect to the two quantities, i.e. σ increases and CMC2 decreases with decreasing values of kcH0 and increasing values of kc and k¯c, respectively. As a result, we demonstrate that the solubilization capacity is predicted to always be higher for a gemini surfactant with CMC2 = 11 mM as compared with a gemini surfactant with CMC2 = 18 mM. The predicted correlation between solubilization capacity and CMC2 agrees with experimental observations showing that surfactants forming larger micelles in general have better solubilization capacity than surfactants forming smaller micelles. The theory also demonstrates, in agreement with experiments, that σ is raised in the entire range of surfactant concentrations, below as well as above CMC2, regardless of micelle size. Consequently, our theory predicts that small micelles formed below CMC2 increase in size, whereas large rodlike or wormlike micelles formed above CMC2 decrease in size, as a hydrophobic solubilizate is added to a micellar solution.

Fractional ionization and size of cetyltrialkyl ammonium bromide and hydroxide micelles as a function of head-group lipophilicity and temperature

We have measured the diffusion coefficients, D, of aqueous micelles formed by cetyltriethyl-, cetyltripropyl- and cetyltributyl-ammonium bromides (CTEABr, CTPABr and CTBABr, respectively) and cetyltriethyl- and cetyltripropyl-ammonium hydroxides (CTEAOH and CTPAOH, respectively) by dynamic light scattering (DLS) at several temperatures from 15 to 55 °C and a range of surfactant (0.01–0.05 M) and salt (0.02–0.06 M NaBr; 0.05–0.3 M NaOH) concentrations. From values of D, we derived the respective fractional ionization values of micellar surfaces. For surfactants with bromide counterion we obtained fits of the diffusivity data using the linear interaction/DLVO approach, thus yielding estimates of the micellar hydrodynamic radius, Rh, and the micellar fractional ionization, α, which ranged from 0.26 to 0.35. For CTEAOH and CTPAOH, the fits appeared to be poorly sensitive to changes in the London-Van der Waals interactions, as expressed by the Hamaker constant, and only a large fractional ionization could account for the observed diffusivities.

Competitive Adsorption between Nanoparticles and Surface Active Ions for the Oil-Water Interface.

Nanoparticles (NPs) can add functionality (e.g., catalytic, optical, rheological) to an oil-water interface. Adsorption of ∼10 nm NPs can be reversible; however, the mechanisms for adsorption and its effects on surface pressure remain poorly understood. Here we demonstrate how the competitive reversible adsorption of NPs and surfactants at fluid interfaces can lead to independent control of both the adsorbed amount and surface pressure. In contrast to prior work, both species investigated (NPs and surfactants) interact reversibly with the interface and without the surface active species binding to NPs. Independent measurements of the adsorption and surface pressure isotherms allow determination of the equation of state (EOS) of the interface under conditions where the NPs and surfactants are both in dynamic equilibrium with the bulk phase. The adsorption and surface pressure measurements are performed with gold NPs of two different sizes (5 and 10 nm), at two pH values, and across a wide concentration range of surfactant (tetrapentylammonium, TPeA+) and NPs. We show that free surface active ions compete with NPs for the interface and give rise to larger surface pressures upon the adsorption of NPs. Through a competitive adsorption model, we decouple the contributions of NPs wetting at the interface and their surface activity on the measured surface pressure. We also demonstrate reversible control of adsorbed amount via changes in the surfactant concentration or the aqueous phase pH.

Performance Evaluation and Application of the Surfactant Combinations showing Ultra-low Oil-Water Interfacial Tensions

Abstract In order to select a surfactant formulation with an ultra-low oil-water interfacial tension for application in a low permeability oil field, surfactant combinations were developed consisting of non-ionic alkanolamides, anionic alkyl benzene sulfonate and betaine in certain proportions. The results showed that the oil-water interfacial tension (oil from the Changing Jing'an field) could decease to 10−4 mN m−1∼10−5 mN m−1 in the wide surfactant concentration range of 0.3%∼0.6% and a salinity of 100 000 mg L−1 at 40°C∼70°C. From 2012 to 2013, the field tests of 8 injection and 39 production wells were carried out. The water-cut escalating rate decreased from + 1.26% to −0.15% monthly. The yield changing rate increased from −1.59% monthly to + 0.12%. The valid period of the test was more than 10 months. The improved oil recovery of the in-test well groups were predicted to increase 6.3% using type A characteristic curve of drive water. When comparing the three injection technologies, the key to the success of field application of surfactant combinations having an ultra-low oil-to-water interfacial tension is a consistent profile protocol of water injection.

Insights into the complex interaction between hydrophilic nanoparticles and ionic surfactants at the liquid/air interface.

Combinations of nanoparticles and surfactants have been widely employed in many industrial processes, i.e., boiling and condensation in heat transfer and hydraulic fracturing in shale oil and gas production, etc. However, the underlying mechanism for various phenomena resulting from the addition of nanoparticles into the surfactant solutions is still unclear. For instance, there are contradictory conclusions from the literature regarding the variations of surface tension upon the addition of nanoparticles into surfactant solutions. In this work, the dominating factors determining if the surface activity of the surfactant solution will increase or conversely decrease when adding certain kinds of nanoparticles have been investigated. Two typical hydrophilic nanoparticles, SiO2 and TiO2 with anionic or cationic surfactants, respectively, have been considered. The surface tension has been measured in a wide range of nanoparticle and surfactant concentrations. It was found that the surface tension of the ionic surfactant solution can be further reduced only if nanoparticles of the same charge were added. For instance, a system containing 0.25 CMC SDS and 1 wt% SiO2 behaves similar to a 0.34 CMC SDS-only solution. Interestingly, the observed synergistic effect is found to be more significant if the surfactant concentration is much lower than its CMC for a given nanoparticle content. Moreover, the effect is perfectly reversible. When the nanoparticles were separated from the system, the surface tension values recovered fully to that of the pure surfactants. If nanoparticles of opposite charge were added, however, the surface tension of the surfactant solution increased. Zeta potential measurement and centrifugal treatment have been employed to reveal the interplay between nanoparticles and surfactants and the adsorption behavior of their assemblies at the liquid/air interface. Based on the experimental outcomes, a possible physical mechanism was proposed. It was concluded that the electrostatic repulsion between surfactant molecules and nanoparticles should be the dominant factor responsible for the observed reversible synergistic effect. Our study is expected to contribute to a better understanding of the interfacial phenomenon in nanoparticle-surfactant complex systems.

The application of Brij 35 in biofiltration of the air polluted with toluene vapours

Removal of certain organic pollutants from the environment may be hindered due to their weak water solubility and high vapour pressure. In particular, these are factors that limit the application of biological methods in remediation since they have an influence on the bio-accessibility of the xenobiotics. For that reason, we carried out research on the use of surface-active agents that have impact on the increase in solubility of hydrophobic compounds. In this publication, we present the results of laboratory tests on the application of Brij 35 in purification of the air polluted with toluene vapours by the biofiltration method. Within the range of surfactant concentrations subjected to the research (200, 300, 400 mg/dm3), we observed an improvement of the removal efficiency as compared to the control series (without the surfactant).

Tuning Nanoparticle-Micelle Interactions and Resultant Phase Behavior.

The evolution of the interaction between an anionic nanoparticle and a nonionic surfactant and their resultant phase behavior in aqueous solution in the presence of electrolyte and ionic surfactants have been studied. The mixed system of anionic silica nanoparticles (Ludox LS30) with nonionic surfactant decaethylene glycol monododecylether (C12E10) forms a highly stable clear phase over a wide concentration range of surfactant. Small-angle neutron scattering (SANS) and dynamic light scattering data show that the surfactant micelles adsorb on the surface of the nanoparticle, resulting in micellar-decorated nanoparticle structures. With the addition of a small amount of electrolyte into this system, the stability gets disturbed substantially and turns to a two-phase (turbid) system. The evolution of interaction in this system has been examined, and it was found that micelle-induced long-range depletion attraction (modeled by a double Yukawa potential) between nanoparticles leads to their aggregation. Interestingly, the addition of anionic surfactant sodium dodecyl sulfate (SDS) in this two-phase system transforms it to a transparent one-phase state, suppressing the depletion-mediated aggregation of nanoparticles. This is attributed to the formation of anionic C12E10-SDS mixed micelles, and it is their repulsive micelle-micelle interaction that disrupts the depletion phenomenon. On the other hand, the addition of cationic surfactant dodecyl trimethylammonium bromide (DTAB) to the turbid LS30-C12E10 electrolyte system shows no change in the turbidity arising from an aggregated nanoparticle system. The driving interaction, in this case, is different from that of the surfactant-mediated depletion attraction; it is due to the attraction between the nanoparticles mediated by the presence of oppositely charged DTAB micelles between them, resulting in a charge-driven bridging aggregation of nanoparticles. Each of these multicomponent systems has been investigated using contrast variation SANS measurements for different contrast conditions where the role of individual components (nanoparticle or surfactant) in the mixed system has been selectively studied. These results thus show that nanoparticle-surfactant micelle interactions can be tuned by the presence of electrolyte and/or choice of surfactant combination.

Effect of Surfactants on Electrodeposition of the Sn–Ni Alloy from Oxalate Solutions

The effects of surfactants on the electrolytic deposition of tin–nickel alloys from oxalate–ammonium electrolytes were determined. The adsorption of the nonionic surfactant at the interface decreases the rate of charge transfer across the interface. As a result, the electrochemical stage of the electroreduction of metals slows down, and the alloy is deposited in the form of shiny finely crystalline coatings. The range of optimum surfactant concentrations in the oxalate–ammonium electrolyte was determined based on the simulation of the interface impedance obtained during the alloy deposition and the electron microscopy studies of the obtained coatings.

Effect of surfactant concentration on the responsiveness of a thermoresponsive copolymer/surfactant mixture with potential application on “Smart” foams formulations

HypothesisPrevious efforts to formulate smart foams composed of mixtures of PNIPAAm, a thermoresponsive uncharged polymer, and surfactants have failed because the surfactant displaces the PNIPAAm from the liquid-air interface, removing the thermal responsiveness. We hypothesized that thermoresponsive foams could be formulated with such a mixture if a charged surfactant were used in order to anchor an oppositely charged brush-type polyelectrolyte, for which PNIPAAm could be incorporated as side chains, to the interface. ExperimentsA brush-type negatively charged co-polyelectrolyte (Cop-L) with PNIPAAm as side chains was synthetized. Its mixtures with DTAB, a cationic surfactant, in aqueous solution were characterized by dynamic light scattering, surface tension and surface compression viscoelasticity measurements, as a function of both surfactant concentration and temperature. The foam stability and its responsiveness to temperature changes were studied with a homemade apparatus. FindingsThe Cop-L/DTAB mixtures were capable of producing thermoresponsive foams but only in a very narrow surfactant concentration (cs) range, 0.3 < cs< 1.6 mM. The responsiveness is due to a modification of the interfacial compression elasticity induced by conformational changes of the Polyeletrolyte/surfactant aggregates at the interface. This is possible only for cs < 1.6 because higher surfactant concentrations induce the polymer collapse at all temperatures, eliminating the thermal responsiveness.

Lysozyme-surfactant adsorption at the aqueous-air and aqueous-organic liquid interfaces as studied by tritium probe

Self-organization of proteins and non-ionic surfactants at the aqueous-air and aqueous-organic liquid interfaces is controlled by hydrophobic interactions. Unfortunately, little is quantitatively known about the effects of high- and low-molecular weight non-ionic surfactants on protein adsorption and aggregation at aqueous-air and aqueous-organic liquid interfaces. A tritium probe technique was applied to the systems lysozyme – Pluronic P123 and lysozyme – Brij-35. For complex analysis, UV and fluorescent spectrometry were also used for solutions with the chosen protein and surfactants concentrations. Non-ionic surfactants form a flexible complex with lysozyme at the aqueous-air interface. We observed that both Pluronic P123 and Brij-35 result in displacement of 40–75 % of protein, even in a surfactant concentration range less than the CMC and rotation of residual protein (or protein in complex with surfactant) in the mixed adsorption layer compared to the adsorption layer formed by free lysozyme. In the mixed adsorption layer, lysozyme globules are separated, and protein becomes more available for tritium atoms compared to free lysozyme.

Combined Molecular Dynamics Simulation-Molecular-Thermodynamic Theory Framework for Predicting Surface Tensions.

A molecular modeling approach is presented with a focus on quantitative predictions of the surface tension of aqueous surfactant solutions. The approach combines classical Molecular Dynamics (MD) simulations with a molecular-thermodynamic theory (MTT) [ Y. J. Nikas, S. Puvvada, D. Blankschtein, Langmuir 1992 , 8 , 2680 ]. The MD component is used to calculate thermodynamic and molecular parameters that are needed in the MTT model to determine the surface tension isotherm. The MD/MTT approach provides the important link between the surfactant bulk concentration, the experimental control parameter, and the surfactant surface concentration, the MD control parameter. We demonstrate the capability of the MD/MTT modeling approach on nonionic alkyl polyethylene glycol surfactants at the air-water interface and observe reasonable agreement of the predicted surface tensions and the experimental surface tension data over a wide range of surfactant concentrations below the critical micelle concentration. Our modeling approach can be extended to ionic surfactants and their mixtures with both ionic and nonionic surfactants at liquid-liquid interfaces.

Study on interactions of cationic gemini surfactants with folded and unfolded bovine serum albumin: Effect of spacer group of surfactants

Interactions of three cationic gemini surfactants, 12-4-12, 2Br− 12-8-12, 2Br− and 12-4(OH)-12, 2Br− with natured and denatured protein, bovine serum albumin (BSA) have been studied by means of UV–Visible absorption, steady-state and time-resolved fluorescence, and circular dichromism (CD) spectroscopy. CD spectroscopic study shows the change in the α-helix and β-strand content of protein with the concentration of gemini surfactants. Gemini surfactant with hydroxyl group in the spacer decreases the α-helix of the BSA more efficiently than that without hydroxyl group in the spacer. Efficiency to decrease the α-helix of the protein increases with decreasing the hydrophobicity of the spacer group of the surfactants at lower concentration range following the order, 12-8-12, 2Br−<12-4-12, 2Br−<12-4(OH)-12, 2Br−. However, at higher concentration range of surfactant, the increasing order of providing hydrophobic environment to tryptophan (Trp) and tyrosine (Tyr) residues of the protein is as follows: 12-4(OH)-12<12-4-12<12-8-12. Gemini surfactant with hydrophobic spacer group provides more hydrophobic environment around Trp and Typ residues of the protein forming micelles like structures along the protein chain. In this concentration range, 12-8-12, 2Br− interacts differently as compared to other two surfactants which are evidenced by the data on excited state lifetime of the protein. It is more efficient to form a particular conformer and/or puckerd ring of Trp as compared to other two surfactants. The microenvironment around Trp residues of BSA is perturbed to a greater extent than that around Tyr residues in presence of gemini surfactants. Fluorescence from Trp and Tyr are quenched by acrylamide to a greater extent in presence of 12-8-12, 2Br−. Interactions of denatured BSA with gemini surfactants also have been studied. 12-8-12, 2Br− even interacts with the BSA unfolded by guanidine hydrochloride (GdHCl) to a greater extent than that by 12-4-12, 2Br− and 12-4(OH)-12, 2Br−.

Coacervate of Polyacrylamide and Cationic Gemini Surfactant for the Extraction of Methyl Orange from Aqueous Solution.

Coacervation in aqueous solution of the mixture of cationic ammonium surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) and 10% hydrolyzed polyacrylamide (PAM) has been investigated. It was found that the 12-6-12/PAM mixture forms coacervate with a large network structure over a wide concentration range of surfactant and polyelectrolyte and shows great efficiency in the extraction of Methyl Orange (MO) from water owing to the cooperation of hydrophobic, electrostatic, and π-cation interactions. Meanwhile, the dye joins the coacervate and strengthens the network structure of the coacervate. In particular, benefiting from partial excess of 12-6-12 molecules, the coacervate phase presents selective adsorption behavior toward anionic dye MO in the presence of cationic dye methylene blue (MB). Furthermore, the coacervate phase is utilized to modify quartz sand and melamine foam, and the coacervate-treated adsorbents can adsorb MO efficiently. Moreover, the MO-loaded adsorbents are easily regenerated with hydrochloric acid, making this an inexpensive and environmentally benign process. These findings offer a simple and effective alternative for the treatment of dye contaminated water and the recovery of dyes.

Improving performances of double-chain single-head surfactants for SP flooding by combining with conventional anionic surfactants

ABSTRACTThe binary surfactant mixtures of 1,3-dialkyl (diC8-diC12) glyceryl ether ethoxylates with didodecylmethylhydroxylpropyl sulfobetaine (diC12HSB) are good formulations for surfactant–polymer flooding of Daqing crude oil, China, but suffer from low aqueous solubility. By combining with α-olefin sulfonates (AOS) at small molar fractions, the aqueous solubility of the formulations can be significantly improved due to the formation of charged mixed micelles. The ternary formulations can reduce Daqing crude oil/connate water interfacial tension to ultralow at a wide range of total surfactant concentration (0.625 ∼ 10 mM), have good resistance to adsorption by sandstone, and can keep sandstone surface water-wet.

Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations

Molecular dynamics simulations of a coarse-grained model are used to study the formation mechanism of periodic mesoporous silica over a wide range of cationic surfactant concentrations. This follows up on an earlier study of systems with low surfactant concentrations. We started by studying the phase diagram of the surfactant–water system and found that our model shows good qualitative agreement with experiments with respect to the surfactant concentrations where various phases appear. We then considered the impact of silicate species upon the morphologies formed. We have found that even in concentrated surfactant systems—in the concentration range where pure surfactant solutions yield a liquid crystal phase—the liquid-crystal templating mechanism is not viable because the preformed liquid crystal collapses as silica monomers are added into the solution. Upon the addition of silica dimers, a new phase-separated hexagonal array is formed. The preformed liquid crystals were found to be unstable in the prese...

Removal of copper ions from aqueous solutions by means of micellar-enhanced ultrafiltration

The aim of the study was to assess the usefulness of micellar–enhanced ultrafiltration (MEUF) for removal of copper ions from water solutions in comparison with classic ultrafiltration process. The tests were conducted in a semi–pilot membrane installation with the use of ultrafiltration module KOCH/ROMICON® at a transmembrane pressure of 0.05 MPa. The effect of concentration of copper ions on ultrafiltration process efficiency was investigated. The second part of the tests concerned the removal of copper ions by MEUF under wide range of anionic surfactant concentration (0.25, 1, and 5 CMC (critical micelle concentration)). Concentration of copper ions in model solutions was equal to 5, 20, and 50 mg Cu/L. Furthermore, the effect of surfactant leakage to the permeate side during filtration was evaluated. Conducted experiments confirmed effectiveness of MEUF in copper ions removal. For the highest copper concentration in the feed (i.e. 50 mg/L), the average concentration of copper ions in the permeate ranged from 1.2–4.7 mg Cu/L depending on surfactant concentration. During filtration experiments, UF module exhibited stable transport properties for model solutions containing copper. For the highest concentration of metal, the decrease of permeate flux did not exceed 11% after 60 minutes of filtration. In the presence of the surfactant, a slight deterioration of transport properties was observed.

19 F NMR matrix-assisted DOSY: a versatile tool for differentiating fluorinated species in mixtures.

NMR is the most versatile tool for the analysis of organic compounds and, in combination with Diffusion-Ordered Spectroscopy ('DOSY'), can give information on compounds in complex mixtures without the need for physical separation. In mixtures where the components' diffusion coefficients are nearly identical, for example because of similar sizes, Matrix-Assisted DOSY ('MAD') can help separate the signals of different constituents, resolving their spectra. Unfortunately, DOSY (including MAD) typically fails where signals overlap, as is common in 1 H NMR. Using 19 F NMR avoids such problems, because the great sensitivity of the 19 F chemical shift to local environment leads to very well-dispersed spectra. Another advantage is the absence of any 19 F background signals from the matrices typically used, avoiding interference with the analyte signals. In this study, differentiation among fluorophenol and fluoroaniline isomers was evaluated using normal and reverse micelles-of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and dioctyl sodium sulfosuccinate (AOT)-as matrices. These surfactants provide useful diffusion separation in these difficult mixtures, with all the solutes interacting with the matrices to different extents, in some cases leading to differences in diffusion coefficient of more than 30%. The best matrices for separating the signals of both acid and basic species were shown to be AOT and CTAB, which are useful over a wide range of surfactant concentration. Copyright © 2016 John Wiley & Sons, Ltd.