Abstract:The structure of aggregates of a new bolaform surfactant [α‐ω (4,7,10,13‐pentaoxa‐16‐azacyclooctadecane) hexadecane] in neat aqueous solution has been investigated by small‐angle neutron scattering. Preliminary data analysis unequivocally indicates that globular micelles are formed. This finding has been confirmed by the analysis of data obtained upon addition of hydrochloric acid. The observed significant reduction of micelle aggregation number has been attributed to the peculiar complexing ability of the two… Show more
“…In solution, it selectively complexes some cations, depending on their relative size, charge, and concentration. , Other examples of amphiphilic molecules able to form metal complexes are reported in the literature. − 1 Schematic representation of some possible Bola C-16 monomer conformations. Redrawn from ref .…”
Section: Introductionmentioning
confidence: 93%
“…To shed light on such a technologically relevant product, useful in ion removal from polluted waters, we present and discuss the results obtained by small angle neutron scattering (SANS) experiments on solutions containing Bola C-16. In a previous work, through comparison of the scattering patterns obtained from sonicated samples (30, 60, and 90 min) with those obtained from the nonsonicated one, it was inferred that the surfactant forms stable globular aggregates.…”
Aq. solns. contg. a bolaform surfactant [α,ω-(4,7,10,13-pentaoxa-16-azacyclooctadecane)hexadecane], with and without electrolytes were investigated as a function of surfactant concn. and ionic strength. Small angle neutron scattering (SANS), NMR self-diffusion, and other phys.-chem. methods were used. From the anal. of SANS data it was inferred that in water the surfactant forms slightly charged ellipsoidal micelles, because of the partial hydrolysis of amino groups. The aggregates grow with the increase of concn., becoming more elongated. Due to the selective complexing ability of aza crown ether units, significant differences were obsd. upon addn. of LiCl, NaCl, and HCl. LiCl gives rise only to a screening of electrostatic repulsion between micelles. NaCl, in addn. to the screening effect, induces a redn. of micelle aggregation no. as a consequence of the increased repulsion between charged headgroups. The micelle size redn. is much stronger in the presence of HCl, which screens the micelle interactions once the surfactant is completely in ionic form. The aforementioned effects increase, as expected, on increasing the electrolyte concn. They are in line with information on the complexation of sodium and proton by the aza crown units, inferred by ionic cond. and potentiometric findings
“…In solution, it selectively complexes some cations, depending on their relative size, charge, and concentration. , Other examples of amphiphilic molecules able to form metal complexes are reported in the literature. − 1 Schematic representation of some possible Bola C-16 monomer conformations. Redrawn from ref .…”
Section: Introductionmentioning
confidence: 93%
“…To shed light on such a technologically relevant product, useful in ion removal from polluted waters, we present and discuss the results obtained by small angle neutron scattering (SANS) experiments on solutions containing Bola C-16. In a previous work, through comparison of the scattering patterns obtained from sonicated samples (30, 60, and 90 min) with those obtained from the nonsonicated one, it was inferred that the surfactant forms stable globular aggregates.…”
Aq. solns. contg. a bolaform surfactant [α,ω-(4,7,10,13-pentaoxa-16-azacyclooctadecane)hexadecane], with and without electrolytes were investigated as a function of surfactant concn. and ionic strength. Small angle neutron scattering (SANS), NMR self-diffusion, and other phys.-chem. methods were used. From the anal. of SANS data it was inferred that in water the surfactant forms slightly charged ellipsoidal micelles, because of the partial hydrolysis of amino groups. The aggregates grow with the increase of concn., becoming more elongated. Due to the selective complexing ability of aza crown ether units, significant differences were obsd. upon addn. of LiCl, NaCl, and HCl. LiCl gives rise only to a screening of electrostatic repulsion between micelles. NaCl, in addn. to the screening effect, induces a redn. of micelle aggregation no. as a consequence of the increased repulsion between charged headgroups. The micelle size redn. is much stronger in the presence of HCl, which screens the micelle interactions once the surfactant is completely in ionic form. The aforementioned effects increase, as expected, on increasing the electrolyte concn. They are in line with information on the complexation of sodium and proton by the aza crown units, inferred by ionic cond. and potentiometric findings
“…To reduce the number of fitting parameters, C terms in eq 11 were evaluated from the slope of the linear regression of Q 4 I(Q) versus Q 4 in the Porod region of the scattering curve. 51 S(Q) was calculated by the rescaled mean spherical approximation 52,53 (RMSA), assuming the interaction potential to be the sum of hard-sphere and Coulombic contributions for both Bola C-16 and SDS. Details of the computational procedures are given elsewhere.…”
Section: Resultsmentioning
confidence: 99%
“…A model reported in previous work 10,52 is used in the computation of the form factor for Bola C-16 micelles. It is the result of an optimization procedure accounting for the possible molecular conformations of Bola C-16.…”
Section: Resultsmentioning
confidence: 99%
“…S ( Q ) was calculated by the rescaled mean spherical approximation , (RMSA), assuming the interaction potential to be the sum of hard-sphere and Coulombic contributions for both Bola C-16 and SDS. Details of the computational procedures are given elsewhere …”
Mixtures composed of water, sodium dodecyl sulfate (SDS), and a bolaform surfactant with two aza-crown ethers as polar headgroups (termed Bola C-16) were investigated by modulating the mole ratios between the components. The two surfactants have ionic and nonionic, but ionizable, headgroups, respectively. The ionization is due to the complexation of alkali ions by the aza-crown ether unit(s). Structural, thermodynamic, and transport properties of the above mixtures were investigated. Results from surface tension, translational self-diffusion, and small angle neutron scattering (SANS) are reported and discussed. Interactions between the two surfactants to form mixed micelles result in a combination of electrostatic and hydrophobic contributions. These effects are reflected in the size and shape of the aggregates as well as in transport properties. The translational diffusion of the components in mixed micelles, in particular, depends on the Bola C-16/SDS mole ratio. Nonideality of mixing of the two components was inferred from the dependence of the critical micelle concentration, cmc, on the mole fraction of Bola C-16. This behavior is also reflected in surface adsorption and in the area per polar headgroup at the air-water interface. SANS data analysis for the pure components gives results in good agreement with previous findings. An analysis of data relative to mixed systems allows us to compute some structural parameters of the mixed aggregates. The dependence of aggregation numbers, nu(T), on the Bola C-16/SDS mole ratio displays a maximum that depends on the overall surfactant content and is rationalized in terms of the nonideality of mixing. Aggregates grow perpendicularly to the major rotation axis, as formerly observed in the Bola C-16 system, and become progressively ellipsoidal in shape.
The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.
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