Surfactant Aerosol OT Research Articles

Combined application of surfactants and iron-based metal–organic framework nanoparticles for targeted delivery of insecticides

With the development of smart delivery systems for pesticides, many studies revealed that nanodelivery methods have great potential for use in efficient and sustainable agriculture; however, field application of the nanopesticides is still a challenge. In this study, the application of a chlorfenapyr (CF)-loaded iron-based metal–organic framework (CF@MIL-101-SL) to maize and its control efficacy for Spodoptera frugiperda were investigated in detail. The results showed that, compared with a suspension concentrate of CF (CF-SC), a solution of CF@MIL-101-SL with the surfactant aerosol OT exhibited excellent wetting, deposition and adhesion with maize leaves. The CF@MIL-101-SL NPs exhibited bidirectional translocation in maize, which significantly enhanced the transport of CF to the target tissues. Field trials revealed that CF@MIL-101-SL maintained > 75 % control efficiency after 21 d of spraying, indicating significantly greater insecticidal activity and persistence than CF-SC. Spray application of CF@MIL-101-SL gave high initial deposition rates, long half-lives on tender and old leaves and significantly reduced pesticide drift into the environment. Based on a biosafety assessment, spraying with CF@MIL-101-SL reduced the negative effects of CF on plants during the growth period. In addition, CF@MIL-101-SL increased the survival rate of Harmonia axyridis larvae and reduced the impacts of CF on the growth and intestinal damage of Harmonia axyridis. In summary, these results highlight the advantages of metal–organic framework delivery systems for multidimensional enhancement of pesticide efficacy, persistence, and safety and provide data on field application and the environmental risks of nanodelivery systems.

Hidden Beneath the Layers: Extending the Core/Shell Model of Reverse Micelles.

Reverse micelles (RMs) provide a unique and highly tunable model system to study water in confined environments. The complex properties of water within RMs arise from the disruption of extended hydrogen bond (H-bond) networks that mediate local and long-range dynamics in bulk aqueous systems. Modulating the water pool size influences its H-bond dynamics, with smaller RMs increasingly restricting the H-bond network rearrangements leading to slower dynamics; however, within small confined systems, the dynamics of the surfactants also influence the water dynamics. Using ultrafast two-dimensional infrared spectroscopy, we investigate the effects of RM size on the surfactant headgroup rotamer populations and picosecond interfacial H-bond dynamics of aerosol-OT surfactants. We find that the increased water penetration accelerates H-bond dynamics, with larger RMs showing faster dynamics. These results imply that the changes in the RM structure alter the physical structure of the RM interface and thus alter the solvation dynamics. The findings in this study can be used for developing models for structure-specific solvation dynamics that account for the surfactant packing and hydration at the interface.

Short-chain branched sulfosuccinate as a missing link between surfactants and hydrotropes.

Surfactants aggregate in water into micelles, and these micelles incorporate organic substances to solubilize them. Hydrotropes are compounds that increase the solubility of hydrophobic substances in water without this form of aggregation. Decreasing the chain length of the classical surfactant Aerosol OT (AOT) from C8 to C5 results in a molecule with intermediate properties. Molecular dynamics simulations and surface tension measurements are performed on this short chain derivative of AOT. This compound shows high solubility and at the same time progressive weak aggregation. The hydration of head groups hinders significant plunging into a hydrophobic core, which leads to well defined liquid chain nanodomains. The transition to bicontinuous aggregates is in the concentration range of 1 mol L-1. The sulfonate group of the head groups (placed at the water interface of worm-like aggregates) rather than the aggregate-aggregate interaction is responsible for the unusual small angle X-ray scattering pattern.

Adsorption kinetics of the partially dissociated anionic surfactant Aerosol-OT in 10 mM NaCl solution

The adsorption kinetics of anionic surfactant Aerosol-OT (AOT) in 10 mM NaCl solution was investigated by measuring and simulating the dynamic and equilibrium surface tension (ST) data. The relaxation of ST for AOT molecules adsorbing onto a freshly created bubble surface was measured using a video-enhanced pendant bubble tensiometer at eighteen AOT concentrations. The partially ionized Langmuir model was applied to best-fit the dynamic/equilibrium ST data. The subsequent findings revealed that the model with a dissociation degree α of 0.1 − 0.2 described the dynamic and equilibrium ST data very well. This implied that AOT behaved as a partially ionized surfactant in 10 mM NaCl solution. The adsorption for AOT onto a clean air–water interface was found to be either (i) diffusion-controlled with a diffusivity value that varied [between 2.5 and 4.6 (10−6 cm2/s)] depending on the bulk concentration or (ii) mixed-controlled with an adsorption rate constant of 2.4 ± 0.8 (107 cm3/mol.s).

Molecular Dynamics Simulation Insight into Interfacial Stability and Fluidity Properties of Microemulsions.

Although the interfacial properties of microemulsions have been extensively studied in both experimental and simulation research studies, the molecular mechanisms of stability and fluidity about microemulsion are still poorly understood. Herein, we report a molecular dynamics simulation study to elaborate the motion of an emulsion droplet involving dichain surfactant Aerosol OT (AOT) and its dynamics evolution at the oil-water interface. By varying the concentrations of AOT, we show that the interfacial thickness and emulsification rate display a piecewise change as the interfacial coverage increases and the W/O emulsion is more stable than the O/W one while O/W emulsion presents better fluidity. In addition, the dispersed system combined with water/AOT/n-heptane tends to form a W/O microemulsion instead of an O/W microemulsion due to the structural collapse of the latter. This work provides a molecular understanding of microemulsion interfacial stability and fluidity.

Inactivation Mechanism of 1-Ethyl-3-Methylimidazolium-Based Ionic Liquid on β-Glucosidase Produced by Paenibacillus sp. LLZ1 and Enhanced Activity Using a Surfactant

β-Glucosidase (BG) hydrolyzes cellobiose into glucose, and is a vital step in converting ionic liquids (ILs)-pretreated biomass to sustainable biofuels. The inactivation mechanism of BG from Paenibacillus sp. LLZ1 induced by microcrystalline cellulose was explored in various concentrations of ILs, composed of [Emim]+ cation and [DEP]-, [OAc]-, [Br]-, [Cl]-, and [BF4]- anions. The FTIR analysis of inactivated BG indicated that the ILs altered its β-sheet content. Moreover, circular dichroism spectroscopy (CD) suggested that the α-helix content decreased, while the β-sheet content increased with the presence of ILs in general. Interestingly, the secondary structure of BG had almost no change after [Emim]DEP treatment, while ionic liquid [Emim]BF4 treatment caused the irreversible denaturation of BG. Eventually, by adding 0.4 mM of Aerosol OT surfactant, the BG activity was increased by 20.1% in the presence of 25% [Emim]DEP, and the corresponding glucose yield from hydrolysis of cellobiose was increased by 23.9%.

The effect of surfactant micellization on the cytotoxicity of silver nanoparticles stabilized with aerosol-OT

The toxic action of surfactant used as a stabilizer of metal nanoparticles have been studied with the aim to determine separate contributions of surfactant monomers and micelles to cell viability decrease. Basing on (1) the well-known ability of surfactant molecules to form micelles in solution at a critical micelle concentration (CMC) and (2) the results reported in literature, showing that toxicity of various surfactants increases when their concentration exceeds CMC, we supposed that surfactant molecules and micelles may differ in their toxic effect on cells. This supposition was verified on the anionic surfactant aerosol-OT (AOT) used as a stabilizer of silver nanoparticles (AgNPs) in studies of their cytotoxicity on Jurkat cells by means of the MTT test. Two samples of AgNPs stabilized with AOT in concentrations higher (3 mM) and lower (1 mM) than its CMC in water were introduced to the cell medium as water solutions diluted to obtain nanoparticle concentrations in the range 1–7 μg/mL. Cell viability changes were registered after 24 h incubation. It was found that AgNPs of similar average size (about 16 nm), synthesized by the same procedure, introduced to the same concentrations in cell medium, produced a different effect on cell viability. Namely, decrease in cell viability was observed for AgNPs with 3 mM AOT, while no noticeable changes were registered for AgNPs with 1 mM AOT. A similar difference was detected for the corresponding dilutions of 3 mM and 1 mM AOT water solutions. We assumed that the toxicity dependence on AOT concentration originated from the difference in toxic action of the two different AOT forms – molecules (monomers) and micelles – present in the AgNPs and AOT solution. The approach was suggested for estimation of the separate contributions of monomers and micelles to the total AOT toxicity; changes of these contributions with AgNPs or AOT concentration were also determined. The results obtained may prove to be useful in studies of the biological activity of surfactants applied both as nanoparticle stabilizers and as agents working in medicine as suppressors of various infections.

Photophysical properties of 1,2-dihydroxyanthraquinone in AOT reverse micelles

We report photophysical properties of 1,2-dihydroxyanthraquinone (alizarin) confined in methanol-in-oil reverse micelles by steady-state and time-resolved fluorescence spectroscopy. The formation of reverse micelles and confinement of alizarin molecules inside the reverse micelles were confirmed by Raman spectroscopy and fluorescence anisotropy measurements. The emission of alizarin centered at 585 nm showed 2.5–3.0 times increase in intensity in small reverse micelles, and the lifetime was also largely increased compared to those of bulk solution. We conclude that alizarin confined in the core of small reverse micelles has a strong interaction with the sulfonate head group of the surfactant Aerosol OT, and that the emission band at 585 nm originates from the alizarin with the proton partly deprotonated and trapped near the anionic surfactant head groups.

Synthesis and Characterisation of Metallosurfactants as Carbon Dioxide Viscosity Modifier

This paper focuses on a systematic approach to enhance the viscosity of supercritical CO2 (scCO2) for enhanced recovery applications. Recent successful results have shown for the first time that fluorinated surfactants can be used as viscosity modifiers for CO2. Although some fluorinated surfactants have been synthesised, up to now no systematic studies have been carried out toward scCO2 viscosity enhancement and impeded commercial developments of viscosity modifier. Here, metallosurfactant structure design was focused on anionic surfactant analogues of Aerosol -OT (sodium bis (2-ethyexyl) sulfosuccinate). The metallosurfactant were systematically synthesised with modification centred on fluorinated content in surfactant chain with introduction of nickel (Ni2+) and manganese (Co2+) counter ions. The metallosurfactant have been investigated by a range of techniques including Nuclear Magnetic Resonance (NMR) Spectroscopy, UV-Visible Spectroscopy and High-Pressure Viscometer. The result shows that fluorination is a crucial factor influencing Aerosol-OT surfactant analogue compatibility with scCO2. The presence of fluorine in the metallosurfactant chemical structure gives rise to relative scCO2 viscosity. The results obtained are beneficial for expanding CO2 in enhanced oil recovery applications and realising its potential using the most efficient metallosurfactant as CO2 viscosity modifier.

Charging Poly(methyl Methacrylate) Latexes in Nonpolar Solvents: Effect of Particle Concentration.

The electrophoresis of a well-established model system of charged colloids in nonpolar solvents has been studied as a function of particle volume fraction at constant surfactant concentration. Dispersions of poly(12-hydroxystearic acid)-stabilized poly(methyl methacrylate) (PMMA) latexes in dodecane were prepared with added Aerosol OT surfactant as the charging agent. The electrophoretic mobility (μ) of the PMMA latexes is found to decrease with particle concentration. The particles are charged by a small molecule charging agent (AOT) at finite concentration, and this makes the origin of this decrease in μ unclear. There are two suggested explanations. The decrease could either be due to the reservoir of available surfactant being exhausted at high particle concentrations or the interactions between the charged particles at high particle number concentrations. Contrast-variation small-angle neutron scattering measurements of PMMA latexes and deuterated AOT-d34 surfactant in latex core contrast-matched solvent were used to study the former, and electrokinetic modeling was used to study the latter. As the same amount of AOT-d34 is found to be incorporated with the latexes at all volume fractions, the solvodynamic and electrical interactions between particles are determined to be the explanation for the decrease in mobility. These measurements show that, for small latexes, there are interactions between the charged particles at all accessible particle volume fractions and that it is necessary to account for this to accurately determine the electrokinetic ζ potential.

Organized assemblies of AOT determine nanoparticle characteristics and their performance as FRET donors

CdS nanoparticles (NPs) have been synthesized in three organized assemblies formed by the surfactant Aerosol-OT (AOT). Although NP synthesis in AOT reverse micelles is well documented, but AOT regular micelles and gels have not been commonly used for NP synthesis in the past. The NP shape, size and particularly crystallinity are found to bear direct correlation to the type of AOT assembly. These CdS NPs were found to be photoluminescent and participate in very effective fluorescence resonance energy transfer (FRET) with a dye, Ethidium bromide (EB). The efficiency of FRET between CdS NPs and EB is found to depend largely on the location of dye in the surfactant assembly and more significantly on the NP characteristics. This is the first report of preparation of CdS NPs in AOT regular micelles and gels and the first report of FRET between CdS NPs and dye in AOT based organized assemblies.

Adsorption of Aerosol-OT on Sand and Shale at High Sodium Salt Concentration

Surfactant flooding is a method for additional recovery of oil from partially depleted reservoirs by changing the interfacial tension. During the application of surfactant into a reservoir, a certain loss in the high equivalent weight fraction occurs. These surfactant molecules are the most efficient in lowering the interfacial tension between reservoir brine and crude oil. Introducing the surfactant to rock sediment may result in these losses and increase the partition or adsorption of hydrocarbon organic compounds (HOCs) in the rock-water system. The adsorptive behaviour of Aerosol-OT was studied under high salt concentration at room temperature in the presence of sandstone and shale. This study detected the adsorption based on the monitored changes in the initial concentration of the surfactant. The adsorption of the surfactant Aerosol-OT has been investigated using batch adsorption isotherms and the technique of UV-Vis spectroscopy. The objective of the study was to gain further insight into the surfactant adsorption for these adsorbents and to determine the appropriate isotherm model. The equilibrium results showed that the value of concentration changed from 0.03 g/L to the lowest value of 0.0124 g/L, which is lower than half. The batch adsorption isotherms that Aerosol-OT adsorption behaviour followed was found to fit Langmuir-Frandluich model.

Polymer-surfactant nanoparticles for improving oral bioavailability of doxorubicin

The oral bioavailability of several clinically relevant drugs is compromised because of their limited absorption across the gastrointestinal tract. Active efflux of the drug by transporters such as P-glycoprotein (P-gp) present on the luminal side of the intestinal epithelial cells limits drug absorption. Encapsulation of drugs in nanoparticles can reduce transporter-mediated efflux and increase drug absorption. The purpose of this manuscript is to determine if the bioavailability of doxorubicin, a P-gp substrate, could be increased by encapsulation in nanoparticles. We synthesized polymer-surfactant nanoparticles comprised of a sodium alginate core complexed with doxorubicin and stabilized by the surfactant Aerosol OT (AOT). Encapsulation of doxorubicin in nanoparticles improved its transport across cell monolayers as evidenced by Transwell® studies. Drug uptake studies were carried out in cells overexpressing P-gp and those with basal levels of P-gp. These studies revealed that AOT inhibited P-gp activity and improved drug uptake in P-gp expressing cells by ~5-6-fold. Increase in drug uptake was found only in cells expressing P-gp and was limited to P-gp substrates. We also determined the in vivo oral bioavailability of the nanoparticle formulation of doxorubicin in mice. Doxorubicin delivered in the form of nanoparticles had a higher bioavailability relative to that with the free drug. This study shows that the oral bioavailability of P-gp substrates such as doxorubicin can be enhanced by delivering them in AOT-alginate nanoparticles.

Use of reflectance anisotropy spectroscopy for mapping the anisotropy of lyotropic liquid crystal dispersions in formulations

ABSTRACTLyotropic liquid crystal dispersions have commercial importance in the formulation of cleaning products and pharmaceuticals. The anisotropy of such dispersions is an important aspect of their properties and a simple method for measurement would be valuable to formulators. The relatively new optical technique of reflectance anisotropy spectroscopy (RAS) was considered to have potential in this respect. To test the idea, the anisotropy of a binary mixture of an anionic surfactant Aerosol OT (AOT) and glycerol (used as a model for water) was investigated using RAS. The variation in the measured anisotropy parallels the expected behaviour of a dispersion of lyotropic liquid crystals as a function of concentration and temperature. A response surface of anisotropy generated as a function of temperature and surfactant concentration demonstrates the use of RAS as a tool for mapping liquid anisotropy to facilitate the formulation of structured liquids.

Copper nanoparticles in AOT “revisited”-direct micelles versus reverse micelles

For the first time, direct micelles of the surfactant Aerosol-OT (AOT) have been used to synthesize copper nanoparticles. The synthesized nanoparticles are spherical and highly crystalline with diameter 5–10 nm. They show the prominent surface plasmon resonance typical of copper nanoparticles. AOT plays a dual role-initially it provides a site for initiation of reduction and subsequently it acts as a stabilizer for controlled nucleation. For comparison, copper nanoparticles were also synthesized in the well known AOT reverse micelles. Small sized nanoparticles (diameter < 4 nm) were formed. Unlike previous works on copper nanoparticle synthesis in reverse micelles using substituted AOT i.e Cu(AOT)2, in this work unsubstituted Na-AOT was used. This minimizes the adverse effects on stability and shape which arise due to surfactant functionalization. Finally, the most important finding of the present work is that AOT direct micelles are better substrates than reverse micelles for synthesis of stable, spherical and crystalline copper nanoparticles with distinct surface plasmon resonance spectra.

Proton transfer in ionic and neutral reverse micelles.

Proton-transfer kinetics in both ionic and neutral reverse micelles were studied by time-correlated single-photon counting investigations of the fluorescent photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS). Orientational dynamics of dissolved probe molecules in the water pools of the reverse micelles were also investigated by time-dependent fluorescence anisotropy measurements of MPTS, the methoxy derivative of HPTS. These experiments were compared to the same experiments in bulk water. It was found that in ionic reverse micelles (surfactant Aerosol OT, AOT), orientational motion (fluorescence anisotropy decay) of MPTS was relatively unhindered, consistent with MPTS being located in the water core of the reverse micelle away from the water-surfactant interface. In nonionic reverse micelles (surfactant Igepal CO-520, Igepal), however, orientational anisotropy displayed a slow multiexponential decay consistent with wobbling-in-a-cone behavior, indicating MPTS is located at the water-surfactant interface. HPTS proton transfer in ionic reverse micelles followed kinetics qualitatively like those in bulk water, albeit slower, with the long-time power law time dependence associated with recombination of the proton with the dissociated photoacid, suggesting a modified diffusion-controlled process. However, the power law exponents in the ionic reverse micelles are smaller (∼ -0.55) than that in bulk water (-1.1). In neutral reverse micelles, proton-transfer kinetics did not show discernible power law behavior and were best represented by a two-component model with one relatively waterlike population and a population with a faster fluorescence lifetime and negligible proton transfer. We explain the Igepal results on the basis of close association between the probe and the neutral water-surfactant interface, with the probe experiencing a distribution of more and less waterlike environments. In addition, the observation in bulk water of a power law t(-1.1) for diffusion-controlled recombination is in contrast to the theoretical prediction of t(-1.5) and previously reported observations. The difference from prior experimental results is discussed.

Micellization behavior of Aerosol OT in alcohol/water systems.

This paper examines the effects of solvent composition on the micellization behavior of the surfactant Aerosol OT (AOT). The critical micelle concentrations of AOT in the pure solvents methanol, ethanol, propanol, and isopropanol were measured using conductiometric techniques. These solvents were then mixed with water to create solvent spectra from pure alcohol to pure water in 12 increments. Critical micelle concentrations were measured at each solvent composition. Dynamic light scattering was used to verify the presence or absence of micelles in the solvent mixtures. It was found that inverse micelles exist over a range of solvent compositions where εeff < 48 with CMCs increasing with increasing solvent polarity. Micellization was found not to occur when 48 < εeff < 80. Regular micelles formed in pure water, with the measured CMC agreeing with the literature value of 2.25 mM.

Interaction between Surfactants and Colloidal Latexes in Nonpolar Solvents Studied Using Contrast-Variation Small-Angle Neutron Scattering

The interaction between deuterium-labeled Aerosol OT surfactant (AOT-d34) and sterically stabilized poly(methyl methacrylate) (PMMA) latex particles dispersed in nonpolar solvents has been studied using contrast-variation small-angle neutron scattering (CV-SANS). The electrophoretic mobilities (μ) of the latexes have been measured by phase-analysis light scattering, indicating that μ is negative. Two analogues of the stabilizers for the particles have been studied as free polymers in the absence of PMMA latexes: poly(12-hydroxystearic acid) (PHSA) polyester and poly(methyl methacrylate)-graft-poly(12-hydroxystearic acid) (PMMA-graft-PHSA) stabilizer copolymer. The scattering from both PHSA in dodecane and PMMA-graft-PHSA in toluene is consistent with extended polymer chains in good solvents. In dodecane, PMMA-graft-PHSA forms polymer micelles, and SANS is consistent with ellipsoidal aggregates formed of around 50 polymer chains. CV-SANS measurements were performed by measuring SANS from systems of PHSA, PMMA-graft-PHSA, and PMMA latexes with 10 and 100 mM surfactant solutions of AOT-d34 in both polymer/particle and AOT contrast-matched solvent. No excess scattering above the polymer or surfactant was found for PHSA in dodecane or PMMA-graft-PHSA in dodecane and toluene. This indicates that AOT does not significantly interact with the free polymers. Excess scattering was observed for systems with AOT-d34 and PMMA latexes dispersed in particle contrast-matched dodecane, consistent with the penetration of AOT into the PMMA latexes. This indicates that AOT does not interact preferentially with the stabilizing layers but, rather, is present throughout the colloids. Previous research ( Langmuir 2010, 26, 6967-6976 ) suggests that AOT surfactant is located in the latex PHSA-stabilizer layer, but all the results in this study are consistent with AOT poorly interacting with alkyl-stabilizer polymers.

Amide I IR probing of core and shell hydrogen-bond structures in reverse micelles

Abstract The properties of N-methylacetamide (NMA) molecules encapsulated in the reverse micelles (RMs) formed by anionic surfactant aerosol OT (AOT), are studied with vibrational spectroscopy and computation. Vibrational spectra of the amide I′ mode of the fully deuterated NMA-d 7 show gradual increase of peak frequencies and line broadening as the size of RMs decreases. Analyses of the spectral features reveal the presence of three states of NMA-d 7 that correspond to NMA located in the core of water phase (absorption frequency of 1606 cm–1) and two types of interfacial NMA near the surfactant layer (1620 and 1644 cm–1). In larger RMs with water content w 0 = [D2O]/[AOT] ≥ 10, only the first two states are observed, whereas in smaller RMs, the population of the third state grows up to 25 % at w 0 = 2. These results indicate the general validity of the two-state core/shell model for the confined aqueous solution of NMA, with small modifications due to the system-dependent solute-interface interaction. However, simulations of small RM systems with w 0 ≤ 15 show continuous variations of the population, frequency shifts, and the solute-solvent interaction strengths at solute-interface distance less than 4 Å. Thus, the distinction of solute core/shell states tends to be blurred in small RMs but is still effective in interpreting the average spectroscopic observables.

Effects of small ionic amphiphilic additives on reverse microemulsion morphology

HypothesisInitial studies (Hopkins Hatzopoulos et al. (2013)) have shown that ionic hydrotropic additives can drive a sphere-to-cylinder (ellipsoid) transition in water-in-oil (w/o) microemulsions stabilized by the anionic surfactant Aerosol-OT; however the origins of this behaviour remained unclear. Here systematic effects of chemical structure are explored with a new set of hydrotropes, in terms of an aromatic versus a saturated cyclic hydrophobic group, and linear chain length of alkyl carboxylates. It is proposed that hydrotrope-induced microemulsion sphere-to-cylinder (ellipsoid) transitions are linked to additive hydrophobicity, and so a correlation between the bulk aqueous phase critical aggregation concentration (cac) and perturbation of microemulsion structure is expected. ExperimentsWater-in-oil microemulsions were formulated as a function of water content w (= [water]/[AOT]) and concentration of different hydrotropes, being either cyclic (sodium benzoate or sodium cyclohexanoate), or linear chain systems (sodium hexanoate, sodium heptanoate and sodium octanoate). Phase behaviour studies were performed as a function of w, additive type and temperature at total surfactant concentration [ST]=0.10M and constant mole fraction x=0.10 (x=[hydrotrope]/[ST]). Microemulsion domain structures were investigated by small-angle neutron scattering (SANS), and these data were fitted by structural models to yield information on the shapes (spheres, ellipsoids or cylinders) and sizes of the nanodroplets. FindingsUnder the conditions of study hydrotrope chemical structure has a significant effect on microemulsion structure: sodium cyclohexanoate does not induce the formation of cylindrical/ellipsoidal nanodroplets, whereas the aromatic analogue sodium benzoate does. Furthermore, the short chain sodium hexanoate does not cause anisotropic microemulsions, but the more hydrophobic longer chain heptanoate and octanoate analogues do induce sphere-to-ellipsoid transitions. This study shows that underlying microemulsion structures can be tuned by hydrotropes, and that the strength of the effect can be identified with hydrotrope hydrophobicity in terms of the bulk aqueous phase cac.