Effect of sphere to rod transition on the probe microenvironment in sodium dodecyl sulphate micelles: A time resolved fluorescence anisotropy study

The effect of different hydrotropic salts on the microenvironment at the anionic head group region of sodium dodecyl sulphate (SDS) micelle has been studied through time-resolved fluorescence anisotropy measurements of a solubilized probe, coumarin-153 (C153). The organic cations of the hydrotropic salts used in this study, i.e. aniline hydrochloride (AHC) and o-, m- and p-toluidine hydrochlorides (OTHC, MTHC and PTHC, respectively), differ in their charge to size ratio and hydrophobicity. Present study utilizes the sensitivity of the fluorescence technique to understand the changes in the micropolarity and microviscosity experienced by the fluorescent probe, C153, solubilized in the micellar Stern layer, on addition of different hydrotropic salts. Significant changes are observed in the rotational relaxation dynamics of the probe with increasing concentration of the salts. The changes in the rotational relaxation dynamics clearly reflect the sphere to rod transition in the SDS micelles and correspond nicely with the reported results from dynamic light scattering measurements. The growth behavior of SDS micelles is found to be sensitive to the hydrophobicity of the organic cations. The charge to size ratio of the organic cations also indicated to play a role in inducing the sphere to rod transition in the SDS micelles. The interesting observation made from this study is that the sphere to rod transition of SDS micelles is largely facilitated by the presence of the hydrotropic salts and such a transition is successfully indicated by the simple fluorescence anisotropy measurements of a probe in the micelle carried out in the presence of different hydrotropic salts.     

Influence of a hydrophobic diol on the micellar transitions of Pluronic P85 in aqueous solution

Micellization behavior of an amphiphilic ethylene oxide-propylene oxide-ethylene oxide tri-block copolymer Pluronic P85 [(EO)(26)(PO)(39)-(EO)(26)] in aqueous solution and in the presence of a hydrophobic C(14)diol (also known as Surfynol104) was examined by physico-chemical methods such as viscometry, cloud point (CP) and scattering techniques viz. dynamic light scattering (DLS) and small angle neutron scattering (SANS). The addition of diol decreases the cloud point and gelation temperature of aqueous Pluronic P85 copolymer solution. DLS and SANS measurements of the polymer in aqueous solution indicated micellar growth and sphere to rod transition in the presence of diol. Surfynol 104 is a sparingly water soluble diol surfactant with a solubility of approximately 0.1 wt%. However, up on addition to Pluronic solution, diol gets incorporated in the block copolymer micelles and leads to structural transition of the micelles. An increase in the temperature and the presence of added sodium chloride in the solution further enhances this effect. The addition of hydrophobic C(14)diol increases the hydrodynamic size and aggregation numbers of the micellar system. The micellar parameters for the copolymer in the presence of C(14)diol are reported at different temperatures and added sodium chloride concentrations.     

Room temperature sphere-to-rod growth and gelation of PEO-PPO-PEO triblock copolymers in aqueous salt solutions

The effects of NaCl and KF on the sphere-to-rod micellar growth behavior of triblock copolymers having two different compositions, (EO)20(PO)70(EO)20 (P123) and (EO)26(PO)40(EO)26 (P85), have been studied by dynamic light scattering (DLS), small angle neutron scattering (SANS) and dilute solution viscometry. NaCl can effectively tune the sphere-to-rod growth temperature of the micelles of both these copolymers and induce micellar growth down to the room temperature and below. The growth behavior is found to be dependent on the composition of the copolymer as P123 being more hydrophobic shows the room temperature growth in the presence of ethanol at significantly lesser NaCl concentration than the less hydrophobic copolymer P85. DLS studies depict for the first time the growth driven transition of the copolymer solutions from dilute to semi-dilute regime as a function of copolymer and salt concentrations. KF can also induce room temperature growth of the P123 micelles at lesser salt concentration than NaCl but it fails to induce any such growth of the P85 micelles. A pseudo-binary temperature-concentration phase diagram on 15% copolymer solutions shows the variation of the sphere-to-rod transition temperature and the cloud point of the copolymer solutions as a function of salt concentration.     

Micellar Behavior of Polystyrene-Poly(Ethylene Oxide) Diblock Copolymers in Aqueous Media: Effect of Copolymer Composition,Temperature, Salt,and Surfactants

Formation and structure of micelles from two amphiphilic polystyrene-block-poly(ethylene oxide) (PS-PEO) diblock copolymers (PS mol.wt. 1000; PEO mol.wt. 3000 and 5000) were examined by surface tension, viscosity, steady state fluorescence, dynamic light scattering (DLS), small angle neutron scattering (SANS), and cryo-transmission electron microscopy (cryo-TEM). The critical micelle concentration (CMC) of the copolymers in aqueous solution was ca. 0.05%; micelle hydrodynamic diameter was 30–35 nm with a narrow size distribution. SANS studies show that the copolymers form ellipsoidal micelles with semi major axis ～23 nm and semi minor axis ～8 nm. No significant change in the structure was found with temperature and presence of salt. The copolymer micelles interaction with the ionic surfactants sodium dodecyl sulphate (SDS) and dodecyltrimethylammonium bromide (DTAB) was also examined by DLS and SANS.     

Small angle neutron scattering study of sodium dodecyl sulfate micellar growth driven by addition of a hydrotropic salt

The structures of aggregates formed in aqueous solutions of an anionic surfactant, sodium dodecyl sulfate (SDS), with the addition of a cationic hydrotropic salt, p-toluidine hydrochloride (PTHC), have been investigated by small angle neutron scattering (SANS). The SANS spectra exhibit a pronounced peak at low salt concentration, indicating the presence of repulsive intermicellar interactions. Model-independent real space information about the structure is obtained from a generalized indirect Fourier transformation (GIFT) technique in combination with a suitable model for the interparticle structure factor. The interparticle interaction is captured using the rescaled mean spherical approximation (RMSA) closure relation and a Yukawa form of the interaction potential. Further quantification of the geometrical parameters of the micelles was achieved by a complete fit of the SANS data using a prolate ellipsoidal form factor and the RMSA structure factor. The present study shows that PTHC induces a decrease in the fractional charge of the micelles due to adsorption at the micellar surface and consequent growth of the SDS micelles from nearly globular to rodlike as the concentration of PTHC increases.     

Effect of phenol on the aggregation characteristics of an ethylene oxide-propylene oxide triblock copolymer P65 in aqueous solution

The effects of phenol on the micellization, micellar growth, and phase separation of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic P65: EO19 PO30 EO19) in aqueous solution have been studied by cloud point, viscosity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), fluorescence spectroscopy, and small-angle neutron scattering (SANS). Various concentrations of P65 have been chosen to estimate the effect of phenol on different concentration regions of P65. Phenol interacts quite differently at low concentrations (0-2%) than at high concentrations (2-10%) of P65, as per the observation that phenol is more predominant at smaller concentrations of P65. A marked decrease in the cloud points of the P65 solutions is observed in presence of phenol. The critical micelle temperature (CMT) of P65 shows a synergistic effect of phenol on P65 aggregates. Micellar transitions, phase separation, and aggregation behaviours like micellization and micellar growth in the presence of phenol have been observed by combining viscometry, DLS, DSC, and CP. DLS shows that the effect of phenol is predominant at high temperatures. SANS shows a high increase in axial ratio and aggregation numbers in the presence of phenol at fixed concentrations of P65. Fluorescence data illustrate that addition of phenol makes micelles polar but at the same time its favours aggregation. Water-soluble phenol (present in low concentrations) forms aggregates with P65, which can be separated by cloud point extraction, making this study interesting for separation of phenol from the phenol-water system.     

Interaction between casein and sodium dodecyl sulfate

The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) with 2.0 mg/ml casein was first investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and fluorescence spectra. ITC results show that individual SDS molecules first bind to casein micelles by the hydrophobic interaction. The micelle-like SDS aggregate is formed on the casein chains when SDS concentration reaches the critical aggregation concentration (c1), which is far below the critical micellar concentration (cmc) of SDS in the absence of casein. With the further increase of SDS concentration to the saturate binding concentration c2, SDS molecules no longer bind to the casein chains, and free SDS micelles coexist with casein micelles bound with SDS aggregates in the system. DLS results show that the addition of SDS leads to an increase in the hydrodynamic radius of casein micelles with bound surfactant at SDS concentration higher than 4 mM, and also an increase in the casein monomer molecule (or submicelles) at SDS concentration higher than 10 mM. Fluorometric results suggest the addition of SDS leads to some changes in the binding process of hydrophobic probes to casein micelles.     

A phenol-induced structural transition in aqueous cetyltrimethylammonium bromide solution

The effect of phenol on the structure of micellar solution of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) was investigated using viscosity, dynamic light scattering (DLS), small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) techniques. The relative viscosity and apparent hydrodynamic diameters of the micelles in CTAB solution increase initially and then decrease with addition of phenol. SANS studies indicate a prolate ellipsoidal structure of the micelles. The axial ratio of the prolate ellipsoidal micelles increases and then decreases with addition of phenol, consistently with DLS and viscosity measurements. NMR studies confirm the solubilization of phenol to the palisade layer and growth of the micelles at high concentration of phenol as revealed from the broadening of peaks.     

Surfactant/nonionic copolymer interaction: a SLS, DLS, ITC, and NMR investigation

The interactions between an oxyphenylethylene-oxyethylene nonionic diblock copolymer with the anionic surfactant sodium dodecyl sulfate (SDS) have been studied in dilute aqueous solutions by static and dynamic light scattering (SLS and DLS, respectively), isothermal titration calorimetry (ITC), and 13C and self-diffusion nuclear magnetic resonance techniques. The studied copolymer, S20E67, where S denotes the hydrophobic styrene oxide unit and E the hydrophilic oxyethylene unit, forms micelles of 15.6 nm at 25 degrees C, whose core is formed by the styrene oxide chains surrounded by a water swollen polyoxyethylene corona. The S20E67/SDS system has been investigated at a copolymer concentration of 2.5 g dm(-3), for which the copolymer is fully micellized, and with varying surfactant concentration up to approximately 0.15 M. When SDS is added to the solution, two different types of complexes are observed at various surfactant concentrations. From SLS and DLS it can be seen that, at low SDS concentrations, a copolymer-rich surfactant mixed micelle or complex is formed after association of SDS molecules to block copolymer micelles. These interactions give rise to a strong decrease in both light scattering intensity and hydrodynamic radius of the mixed micelles, which has been ascribed to an effective reduction of the complex size, and also an effect arising from the increasing electrostatic repulsion of charged surfactant-copolymer micelles. At higher surfactant concentrations, the copolymer-rich surfactant micelles progressively are destroyed to give surfactant-rich-copolymer micelles, which would be formed by a surfactant micelle bound to one or very few copolymer unimers. ITC data seem to confirm the results of light scattering, showing the dehydration and rehydration processes accompanying the formation and subsequent destruction of the copolymer-rich surfactant mixed micelles. The extent of interaction between the copolymer and the surfactant is seen to involve as much as carbon 3 (C3) of the SDS molecule. Self-diffusion coefficients corroborated light scattering data.     

Partitioning of macrocyclic compounds in a cationic and an anionic micellar solution: a small-angle neutron scattering study

Following a previous investigation on partitioning of some macrocycle compounds in sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) aqueous solutions and their effect on the micellar structure, a small-angle neutron scattering (SANS) study has been performed at fixed surfactant content (0.20 mol/L) and varying macrocycle concentrations from 0.20 up to 1.0 mol/L. Conductivity measurements have been also performed in order to evaluate the effect of the presence of macrocycles on the critical micellar concentration (cmc) of the two surfactants. SANS experimental data were fitted successfully by means of a core-plus-shell monodisperse prolate ellipsoid model. It has been found that 1,4,7,10,13,16-esaoxacyclooctadecane (18C6) and 4,7,13,16-tetraoxa-1,10-diazacyclooctadecane (22) do not interact with DTAB micelles whereas their sodium complexes interact with SDS aggregates and partially localize, as a consequence of electrostatic interaction, on the micellar surface or in the Stern layer. 2,5,8,11,14,17-Hexaoxabicyclo[16.4.0] dicosane (B18C6), as a consequence of the increased hydrophobic character with respect to 18C6, interacts with DTAB hydrocarbon chains and partially localizes in the inner part of micelles. This finding has been successfully used to justify the higher amount of B18C6 compared to the 18C6 one found in the SDS micellar phase. The substituted crown ether has been found localized both on the micelle surface via complex formation and in the inner part of micelles as a consequence of the increased hydrophobic character. For all systems, the aggregate size primarily decreases with the amount of macrocycle in the micellar phase. The interpretation of cmc trends as a function ofmacrocycle concentration gives information on its distribution between micellar and aqueous phases that is in line with SANS results.     

Clouding and Hydrodynamic Behavior of Pluronic-Surfactant Interaction in Aqueous Salt Solutions

Clouding behavior of PEO-PPO-PEO and PPO-PEO-PPO block copolymers were studied in presence of sodium dodecyl sulfate (SDS) and NaCl. Extensive study of Pluronic P84 (EO₁₉PO₄₃EO₁₉) with different salts and ionic surfactants, were carried out using cloud point, viscosity and dynamic light scattering (DLS) measurements. The change in cloud point, as well as the size of P84 micelles in aqueous salt solution obeys the Hofmeister lyotropic series. Results on P84-ionic surfactant mixture indicate stronger interaction in case of SDS compared to those in presence of dodecyl trimethylammonium chloride (DTAC); here interaction seems to diminish in the presence of salts.     

Micellar copolymerization of associative polymers: study of the effect of acrylamide on sodium dodecyl sulfate-poly(propylene oxide) methacrylate mixed micelles

Mixed micelles of sodium dodecyl sulfate (SDS) and poly(propylene oxide) methacrylate (PPOMA) have been studied in the presence of acrylamide using conductimetry, fluorescence spectroscopy, and small-angle neutron scattering (SANS) under the following conditions: (i) the SDS-acrylamide binary system in water; (ii) the SDS-acrylamide-PPOMA ternary system in water. The addition of acrylamide in SDS solutions perturbs the micellization of the surfactant by decreasing the aggregation number of the micelles and increasing their ionization degree. The variations of the various micellar parameters versus the weight ratio R=PPOMA/SDS are different in the presence of acrylamide or in pure water. These differences are much more pronounced for the lower than for the higher PPOMA concentrations. There is competition between acrylamide and PPOMA and at higher PPOMA concentration, acrylamide tends to be released from SDS micelles and is completely replaced by PPOMA.     

Morphological characterization of self-assembled peptide nucleic acid amphiphiles

Peptide nucleic acid amphiphiles (PNAA) are a promising set of materials for sequence-specific separation of nucleic acids from complex mixtures. To implement PNAA in micellar separations, the morphology and size of PNAA micelles in the presence and absence of a sodium dodecyl sulfate (SDS) cosurfactant have been studied by small-angle X-ray scattering and dynamic light scattering. We find that a 6-mer PNAA with a 12-carbon n-alkane tail forms ellipsoidal micelles (a = 5.15 nm; b = 3.20 nm) above its critical micelle concentration (CMC) of 110.9 microM. On addition of a stoichiometric amount of complementary DNA, PNAA hybridizes to DNA, suppressing the formation of PNAA micelles. At a ratio of 19:1 SDS/PNAA (total concentration = 20 mM), spherical micelles are formed with outer radius Rs = 2.67 nm, slightly larger than spherical micelles of pure SDS. Capillary electrophoresis studies show that PNAA/DNA duplexes do not comicellize with SDS micelles. No such effects are observed using noncomplementary DNA. The shape and size of the PNAA micelles is also verified by dynamic light scattering (DLS) studies. These results provide an interesting case study with competing electrostatic, hydrophobic, and hydrogen-bonding interactions in micellar systems and make possible the use of PNAA in micellar separations of DNA oligomers.     

SANS study of tuning of clouding in charged micellar system

We report the phenomenon of clouding in charged micellar solution of sodium dodecyl sulfate (SDS) surfactant with varying concentration of tetrabutylammonium bromide (TBAB) salt. The cloud point (CP) temperature is found to decrease significantly with TBAB concentration. Small-angle neutron scattering (SANS) studies have been performed on these systems to understand the evolution of structure and interaction of micelles prior and after the CP. Data are analyzed using Baxter’s sticky hard-sphere potential between the micelles as approaching the CP. It is found that the attractive potential amongst micelles increases with temperature leading to clustering at CP. Both the micelles and clusters coexist at CP and even at temperatures much higher than CP. The propensity of cluster formation strongly depends on the TBAB concentration where higher TBAB concentration provides smaller temperature range over which the clusters are formed. SANS data from clusters show a Porod scattering in the low-Q region, suggesting a very large size of the clusters. The stability of these clusters against phase separation is examined by the time-dependent SANS and compared for different TBAB concentrations.     

Stopped-flow kinetic studies of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt

The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS], chi(PTHC)=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time, tau(g), for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson-Wall (A-W) theory. At chi(PTHC) > or = 0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtained tau(g) decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. At chi(PTHC)=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at low chi(PTHC) and the sphere-to-rod transition at high chi(PTHC) further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain lengths, the slower the sphere-to-rod transition.     

Micellization of sodium dodecyl sulfate and polyoxyethylene dodecyl ethers in solution

The effect of polyoxyethylene type nonionic surfactants (C₁₂E _n n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of C₁₂E _n , micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence of NaCl. Micellar growth is most significant in presence of shorter moieties of C₁₂E _n (e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm this assumption are reported. The cloud point of C₁₂E _n has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were present.     

Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 2. n-Tetradecyl-beta-D-maltoside

The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-d-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degrees C. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degrees C. Comparison of DLS data in D(2)O and H(2)O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO(4)(2)(-) > Cl(-) > NO(3)(-) > I(-) > SCN(-), where I(-) and SCN(-) act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.     

Polyaniline nanoparticles prepared in rodlike micelles

The effect of aniline hydrochloride (AHC) on the size and shape of sodium dodecyl sulfate (SDS) micelles has been investigated by dynamic light scattering. A monotonic decrease in the diffusion coefficient of the micelles was observed with an increase in AHC at fixed SDS concentration. This was ascribed to prolate ellipsoidal growth of the micelles due to decrease of the effective headgroup area/molecule by adsorption of AHC on SDS micelles. The length of the micelles can be tuned by controlling the ratio of concentrations of AHC to SDS. Polymerization of aniline in micelles of different sizes leads to the formation of colloidal polyaniline with variable sizes. A direct correlation between size ofmicelles and size ofpolyaniline particles was observed. Combination of static and dynamic light scattering experiments reveal that the conformations of the polymer do not change significantly with size of the colloid.     

Variegated micelle surfaces: correlating the microstructure of mixed surfactant micelles with bulk solution properties

Electron paramagnetic resonance, viscosity, and small-angle neutron scattering (SANS) measurements have been used to study the interaction of mixed anionic/nonionic surfactant micelles with the polyampholytic protein gelatin. Sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (C12BNMG) were chosen as "interacting" and "noninteracting" surfactants, respectively; SDS micelles bind strongly to gelatin but C12BNMG micelles do not. Further, the two surfactants interact synergistically in the absence of the gelatin. The effects of total surfactant concentration and surfactant mole fraction have been investigated. Previous work (Griffiths et al. Langmuir 2000, 16 (26), 9983-9990) has shown that above a critical solution mole fraction, mixed micelles bind to gelatin. This critical mole fraction corresponds to a micelle surface that has no displaceable water (Griffiths et al. J. Phys. Chem. B 2001, 105 (31), 7465). On binding of the mixed micelle, the bulk solution viscosity increases, with the viscosity-surfactant concentration behavior being strongly dependent on the solution surfactant mole fraction. The viscosity at a stoichiometry of approximately one micelle per gelatin molecule observed in SDS-rich mixtures scales with the surface area of the micelle occupied by the interacting surfactant, SDS. Below the critical solution mole fraction, there is no significant increase in viscosity with increasing surfactant concentration. Further, the SANS behavior of the gelatin/mixed surfactant systems below the critical micelle mole fraction can be described as a simple summation of those arising from the separate gelatin and binary mixed surfactant micelles. By contrast, for systems above the critical micelle mole fraction, the SANS data cannot be described by such a simple approach. No signature from any unperturbed gelatin could be detected in the gelatin/mixed surfactant system. The gelatin scattering is very similar in form to the surfactant scattering, confirming the widely accepted picture that the polymer "wraps" around the micelle surface. The gelatin scattering in the presence of deuterated surfactants is insensitive to the micelle composition provided the composition is above the critical value, suggesting that the viscosity enhancement observed arises from the number and strength of the micelle-polymer contact points rather than the gelatin conformation per se.     

Formation of monodisperse charged vesicles in mixtures of cationic gemini surfactants and anionic SDS

The aggregation behavior of catanionics formed by the mixture of cationic geminis derived from dodecyltrimethylammonium chloride (DTAC) and anionic sodium dodecylsulfate (SDS) was studied by means of phase studies and comprehensive small-angle neutron scattering (SANS) experiments at 25 °C and 50 mM overall concentration. The results are compared to those for the previously studied SDS + DTAC system. Various gemini spacers of different natures and geometries were used, but all of them had similar lengths: an ethoxy bridge, a double bond, and an aromatic ring binding the two DTACs in three different substitutions (ortho, meta, and para). SANS and SAXS data analysis indicates that the spacer has no large effect on the spheroidal micelles of pure surfactants formed at low concentration in water; however, specific effects appear with the addition of electrolytes. Microstructures formed in the catanionic mixtures are rather strongly dependent on the nature of the spacer. The most important finding is that for the hydrophilic, flexible ethoxy bridge, monodisperse vesicles with a fixed anionic/cationic charge ratio (depending only on the surfactant in excess) are formed. Furthermore, the composition of these vesicles shows that strongly charged aggregates are formed. This study therefore provides new opportunities for developing tailor-made gemini surfactants that allow for the fine tuning of catanionic structures.