Colloids and Surfaces A: Physicochemical and Engineering Aspects 2017 Volume 513() pp:274-279
Publication Date(Web):5 January 2017
DOI:10.1016/j.colsurfa.2016.10.054
•Mixed C22TABr/C18TABr micelles were prepared in ethanol/water (15/85 wt%) solvent.•NaBr was used to inhibit secondary aggregation of the micelles.•The micelles were fixed via the polymerisation of solubilised styrene monomers.The association of mixed docosyltrimethylammobium bromide and octadecyltrimethylammonium bromide, C22TABr/C18TABr, in ethanol (a common solvent favoured for both their alkyl tails and head-groups) induced by the addition of water (a non-solvent for the tails) has been studied using light-scattering measurements. Under the assistance of NaBr, which promoted the surfactant molecules to pack tightly in the micelles, mono-disperse spherical micelles composed of mixed C22TABr/C18TABr were obtained in ethanol/water (15/85 wt%). Styrene was solubilised into the templating C22TABr/C18TABr micelles (βsurf, the molar ratio of C18TABr to C22TABr, was 2.5) and then was polymerised in situ. To achieve a good freezing effect, the amount of styrene solubilised, represented as the molar ratio of styrene monomer to total surfactants, nst/nsurf, was required to be greater than 4.87 for this templating micellar system. The diluting tests demonstrated that, after polymerisation, the styrene-containing micelles froze their microstructure well. Light-scattering measurements, and TEM observation, all indicated that these micelles were mono-dispersed, and retained their spherical shape. As swollen by polystyrene, the micelle had an avarage radius of 18 nm.C22TABr/C18TABr formed mixed micelles in ethanol/water (15/85 wt%) with the assistance of NaBr and styrene were then solubilized and polymerized in situ, by which means the mono-disperse, spherical micelles were frozen.
The reorganization of fumed silica gel formed in sulphuric acid medium after being broken has been studied using rheological measurements including thixotropy, gelling time, and gel strength determination according to the falling rod method. The original gel formed by fumed silica particles was also studied for comparison. The results showed that the segments yielded after the original gel was broken can reorganize into a new gel although its ability was weaker than that of fresh particles. The dispersed size of silica particles influenced both the formation of the original gel and the reorganization behavior. The smaller silica particles favored a prolonged gelling time but yielded a gel with relatively low strength. Comparatively, the tendency to reorganize was weaker than in the original gel formation. The standing temperature during the fresh gel formation showed less of an effect on the reorganization process.
An equally-charged mixture of an anionic gemini surfactant, O,O′-bis(sodium 2-tetradecylcarboxylate)-p-azodiphendiol (G14-azo), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was dissolved in cyclohexane to form reverse worm-like micelles. Samples with different surfactant concentrations and amounts of added water were studied using rheological measurements. The amount of water, represented as the molar ratio of water to total surfactants W0, was c. 13 (at its minimum) in these equally charged systems of G14-azo (200 mmol L−1)/CTAB. The low shear viscosity ηL of this system reached 4370 Pa s at W0 = 13 and the dynamic rheological result showed typical surfactant gel behaviour. Under UV-light irradiation, the transparent sample (G14-azo (300 mmol L−1)/CTAB (600 mmol L−1)) at W0 = 40 became turbid, during which ηL was rapidly reduced from the original 285 Pa s to 0.3 Pa s, indicating a transition of aggregate morphology from reverse worms into simple reverse micelles. Then the sample was returned to its original homogeneous state with c. 290 Pa s viscosity under visible light irradiation. However, this transition cannot be well achieved at low W0 due to the interior cores being too small. This limit has been attributed to both the Gemini type of surfactant molecule and to the inverted structure of aggregates.
A reverse aggregate system composed of oleic acid and diethylenetriamine in cyclohexane has been studied. Small angle X-ray scattering (SAXS) measurements and polarising microscopy (POM) observations suggested the formation of reverse vesicles. FT-IR measurements showed simple attraction between DETA and OA, which increased the size of the head of the forming unit and resulted in reverse vesicle formation. Therefore, the viscosity of solutions depended on the mole ratios of DETA to OA,β, and reached a maximum of 122 Pa s at β = 1 for 1 mol L−1 OA. Dynamic oscillatory sweeps were carried out for this system of equi-mole mixed OA (1 mol L−1) and DETA. Strong elasticity was observed, where the elastic modulus (G′) always dominated over the viscous modulus (G′′) over the range of examined frequencies. The elastic plateau modulus G′P was 127.4 Pa and G′P was found to decrease exponentially with temperature. Strain sweeps exhibited a strain-softening response at high strains. The effect of trace amounts of water was also examined for equi-mole mixed OA (1 mol L−1) and DETA, where the reverse vesicles remained. The water was found to improve the association of DETA with OA and increase the visco-elasticity of the solution. The maximum viscosity was as high as 6005 Pa s at W0 = 6, and G′P also reached 530 Pa. The solution became gelatinous in appearance.
The reverse aggregates formed by mixed zwitterionic surfactant, N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulphonate (abbreviated to SB-12), and non-ionic surfactant, tetraoxyethylene lauryl ether (C12E4), in cyclohexane have been studied using rheological and small angle X-ray scattering (SAXS) measurements and polarised-microscopy (POM) observations. With the help of C12E4 and a trace amount of water, SB-12 was dissolved in cyclohexane to obtain a homogeneous solution. The morphologies of the aggregates depended on the molar ratio of C12E4 to SB-12, β. At β = 1, reverse wormlike micelles were formed, and at β = 2, there were reverse vesicles in the solution. The mechanism underpinning the reverse aggregate formation was discussed. The amount of trace water, represented as the mole ratio of water to total surfactants W0, did not influence the aggregate morphologies.
Co-reporter:Xiaoxiang Sun, Yu Chen and Jianxi Zhao
RSC Advances 2016 vol. 6(Issue 45) pp:38913-38918
Publication Date(Web):13 Apr 2016
DOI:10.1039/C6RA02063A
Commercially available fumed silica (F-SiO2) was hydrophobised in situ via the interaction with a cationic gemini surfactant, ethanediyl-α,ω-bis(tetradecyldimethyl-ammonium bromide) (14-2-14), in aqueous solution. The effect of this surfactant modification was far higher that carried out by its corresponding monomer, tetradecyltrimethylammonium bromide (C14TABr). The mechanism of modification was assumed according to zeta potential measurements and observations of physical appearance. These particles were used to generate and stabilize aqueous foams. Both the foaming efficiency and the stabilising ability of F-SiO2/14-2-14 all exceeded that of F-SiO2/C14TAB. In the gemini case, the synergism and competition between the particles and the free surfactant molecules for their adsorption at the foam film were found, which resulted in two peaks in the foam stability curve. Dilational rheology of the films was measured using an oscillating drop technique. There were also two maxima in the dilational elasticity ε for the F-SiO2/14-2-14 system, respectively corresponding to each maximum in foam stability.
The cloud point (CP) behaviour of a carboxylate gemini surfactant, O,O′-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C12ϕ2C12), in aqueous solution has been examined in the presence of tetra-propyl-ammonium bromide (Pr4NBr), an organic salt with less hydrophobicity than that of commonly used species. The aggregates of C12ϕ2C12 in the solution were investigated by dynamic light scattering (DLS), steady-state fluorescence and rheological measurements. Compared with traditional single chain surfactants, C12ϕ2C12 showed the CP phenomena at very low surfactant concentrations. In the presence of Pr4NBr, C12ϕ2C12 in aqueous solution formed several types of aggregates with different sizes. As the temperature was raised to the CP, the micelles rapidly associated, resulting in a cloud-like appearance of the solution. The mechanism has been attributed to C12ϕ2C12, which can provide an attractive force for the micelle–micelle contact. Namely, with increasing temperature, some of the C12ϕ2C12 molecules within the micelles changed their configuration from cis- to trans-form, leading to some tails of C12ϕ2C12 in aggregates stretching towards the solution. When such micelles approached each other, these projecting tails interacted hydrophobically, and this resulted in the association of the micelles.
Co-reporter:Tianhua Zhou, Shengwei Liu, Yi You, Rong Xu, and Jianxi Zhao
Journal of Chemical & Engineering Data 2016 Volume 61(Issue 9) pp:2915-2922
Publication Date(Web):August 4, 2016
DOI:10.1021/acs.jced.5b00778
The micellization of a homologous series of heterogemini surfactants, CmOhpNCn (m, n = 10, 8; 12, 8; 14, 8; 16, 8; and 10, 14), in aqueous solution and their adsorption at the air/water interface have been investigated by surface tension, conductivity, and fluorescence techniques. The surface tension curves of C16OhpNC8 and C10OhpNC14 showed two break points, corresponding to the critical concentration of the premicellar aggregation and the general micellization, respectively. The results of conductivity and fluorescence spectra using pyrene as probe confirmed the premicellization behavior in the two cases. This indicated that these surfactants have strong aggregation ability in the solution. The micelle formed nearby the cmc displayed only a small aggregation number but a large ionization degree. The C20 that characters the efficiency in surface tension reduction was quite small in comparison with those of conventional surfactant and even smaller than those of symmetric gemini surfactants such as 12-s-12 homologous. The special molecular packing of CmOhpNCn in aqueous solution was closely related to the intermolecular hydrogen bonding and a weak electrostatic repulsion.
Journal of Solution Chemistry 2016 Volume 45( Issue 1) pp:126-139
Publication Date(Web):2016 January
DOI:10.1007/s10953-015-0426-x
The thermodynamics of the micellization of long-tail surfactants, including docosyl-, eicosyl-, and octodecyl-trimethylammobium bromide (C22TABr, C20TABr, and C18TABr), docosylethoxyldimethyl-ammonium bromide (C22(OH)DABr), and docosylbenzyldimethyl-ammobium bromide (C22BzDABr), have been studied using static light scattering measurements in ethanol following addition of water. The water content was found to influence the thermodynamics of micellization. In this study, the surfactants examined were at mmol·L−1 concentrations in ethanol and thereby the critical water content inducing aggregation was always smaller than 50 wt%. All the thermodynamic functions are negative over the concentration range investigated. The micellization is mainly enthalpy- and partly entropy-driven. With continuously increasing water content, the entropic contribution to the driving force increases. The critical water contents leading to the transition from mainly enthalpy-driven to mainly entropy-driven behavior are 66.9 wt% (C22BzDABr), 73.2 wt% (C22TABr), and 77.1 wt% (C22(OH)DABr), respectively. Enthalpy–entropy compensation occurs during the micellization processes. The compensation temperatures Tc are close to the general values for surfactants in aqueous solution.
Journal of Solid State Electrochemistry 2016 Volume 20( Issue 3) pp:657-664
Publication Date(Web):2016 March
DOI:10.1007/s10008-015-3090-6
Commercial-grade fumed silica was dispersed by mechanical shearing and/or ultrasonic force to produce dispersed silica particles with different sizes. The light-scattering technique and a diagrammatic method of extrapolation used to eliminate the influence of particle interaction were applied to determine the size of the particles. Then, the effect of particle size on the gelation of fumed silica in sulphuric acid medium, as well as some electrochemical properties, such as ion transfer and redox capacities of lead, in the gelled electrolyte were examined. The results showed that the size of dispersed particles affected the gelation of fumed silica itself: with increasing size, the thixotropy of the system increased and the gelling time decreased, particularly for those particles obtained only by simple stirring. The strength of the gel increased with increasing particle size. At an identical silica content, the increase in particle size led to a decrease in the density of the particles: this weakened the three-dimensional structure of the silica particle network and reduced the efficiency of ion transfer. However, the effect of silica particle size on the redox capacities of lead was negligible.
An equi-charged mixture of cationic gemini surfactant, C,C′-bis(sodium dodecyldimethylammonium bromide)-p-benzenedimethylene (12-Ph-12), and anionic surfactant, sodium laurate (SL), can be dissolved in cyclohexane to form reverse worm-like micelles. The samples, with their different surfactant concentrations and water contents, were studied using rheological measurements. The minimum value of W0, the molar ratio of water to total surfactants, was 9 for the equally charged system of 12-Ph-12 (200 mmol L−1)/SL. The maximum value of zero-shear viscosity (η0) of this system was 1858 Pa s−1 at W0 = 14. Upon increasing the 12-Ph-12 concentration to 300 mmol L−1, η0 increased rapidly to 2200 Pa s−1. The dynamic rheology showed the typical visco-elastic response of a thread-like micelle solution at 12-Ph-12 (200 mmol L−1) and W0 = 10, with a relaxation time (τR) of 0.11 s. At W0 = 14, a characteristic of a surfactant gel was shown, where the elastic modulus (G′) and the viscous modulus (G″) were independent of frequency. Non-linear visco-elasticity showed a strain-softening response at high strains.
Colloid and Polymer Science 2016 Volume 294( Issue 6) pp:1037-1043
Publication Date(Web):2016 June
DOI:10.1007/s00396-016-3857-z
The self-assembly of polypentadeca- and polyeicosa-oxyethylene mono n-hexadecylethers (C16E15 and C16E20) in cyclohexane has been studied using small-angle X-ray scattering (SAXS), rheology measurements and polarised-microscopy (POM) observations. Both surfactants can dissolve in cyclohexane, which benefited from their low cohesive energy. A trace amount of water was used to help the formation of reverse aggregates. The SAXS measurements and POM observations all evinced the formation of reverse vesicles in the solutions. The solution viscosity showed the dependence on both water content, represented as the mole ratio of water to surfactant W0, and surfactant concentration Cs. The samples at Cs = 200 mmol L−1 and W0 = 15–20 had a visco-elastic response with elastic behaviour at high frequencies (G′ dominating over G″) and slightly viscous behaviour at low frequencies (G″ exceeding G′) which resulted in a crossover of G′ and G″ at below 0.1 rad s−1. The elastic plateau modulus G′P increased with increasing W0 or Cs. The effect of temperature on the rheological properties was examined. The value of flow activation energy, Ea, of C16E20 was lower than that of C16E15, which suggested that the former may be more likely to form reverse vesicles than the latter. The elastic plateau modulus G′P showed temperature dependence, which was explained in terms of the hydrogen bonding interactions between the water and the POE.
Co-reporter:Bing-Lei Song, Xiao-Na Yu, Jian-Xi Zhao and Guo-Jing Sun
RSC Advances 2015 vol. 5(Issue 98) pp:80330-80338
Publication Date(Web):16 Sep 2015
DOI:10.1039/C5RA16799J
Stable foams were generated using a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (12-2-12) together with a linear alcohol, hexanol (C6OH) or heptanol (C7OH), in aqueous solution. The foam stability was determined using the half-life of foam height falling (t1/2) as the index. The results showed that C7OH was more efficient than C6OH together with 12-2-12 to stabilize the foams. To generate the most stable foams, the optimum addition for both C6OH and C7OH was determined. The adsorption of the mixtures at the air/water interface was studied using surface tension measurements. The intermolecular interactions and the composition of the mixed monolayer were estimated by Rubingh–Rosen theory and the surface excess was derived from the Gibbs equation. The total surface excess that included both 12-2-12 and alcohols, was shown to significantly increase following the addition of alcohols suggesting the active molecules were more densely packed at the interface. The interfacial dilational rheology of the films was examined using the oscillating drop technique. The results showed that a highly stable foam always corresponded to a highly elastic adsorption film. The present study suggests a new formula for the generation of highly stable foams using a gemini surfactant with a short spacer together with a linear alcohol.
Colloid and Polymer Science 2015 Volume 293( Issue 12) pp:3545-3554
Publication Date(Web):2015 December
DOI:10.1007/s00396-015-3668-7
The gemini surfactants, O,O’-bis(sodium 2-dodecyl-carboxylate)-p-dibenzenediol and O,O’-bis(sodium 2-decylcarboxylate)-p-dibenzenediol (denoted as C12ϕ2C12 and C10ϕ2C10, respectively), were previously found to form network-like aggregates in very dilute solution. In the present work, the effect of alkyltrimethylammonium bromides, CnNBr, on the network-like aggregates formed by C12ϕ2C12 and C10ϕ2C10 was studied using dynamic light scattering, fluorescence probing, steady-state or frequency sweep rheology, and freeze-fractured TEM measurements. These network-like aggregates were easily transformed into core-shell micelles as CnNBr was added, including spherical micelles and even thread-like micelles, upon increased concentration of CnNBr. On further increasing CnNBr concentration, vesicles were formed. The phase diagrams of aggregate transition were plotted. All of these were attributed to the improvement of added CnNBr on the effective molecule geometry under the base of original columnar-like molecules of C12ϕ2C12/C10ϕ2C10.
Journal of Surfactants and Detergents 2014 Volume 17( Issue 4) pp:583-589
Publication Date(Web):2014 July
DOI:10.1007/s11743-013-1486-9
The effect of quaternary ammonium-based bolaform counterions (Bolan-series where n is the number of carbon atoms between the heads) on the adsorption of sodium dodecyl sulfonate (SDDS) at the air/water interface has been studied using surface tension measurements. The results showed that the Bolan counterions strongly interacted with SDDS even at very low concentrations. This reduced the CMC and C20 in the presence of Bolan counterions. The SDDS packed more tightly at the interface under the inducement of Bolan counterions and thus the occupied area per surfactant molecule decreased. Another bolaform counterion series (Bolanph) with a benzene ring attached on each side of the quaternary ammonium heads could further enhance the interaction with SDDS. This is due to the fact that the attached aromatic rings penetrate into the gaps between the surfactant headgroups, which provide an additional association force besides the electrostatic attractions. The present results suggested an approach to construct gemini-like surfactants depending on the electrostatic attraction between the bolaform counterions and the conventional ionic surfactants or an additional hydrophobic force made by the attached aromatic rings.
Colloid and Polymer Science 2014 Volume 292( Issue 11) pp:2785-2793
Publication Date(Web):2014 November
DOI:10.1007/s00396-014-3293-x
This paper reports a study on the aggregation and rheological behavior of the family of O, O’-bis(sodium 2-alkylcarboxylate)-p-dibenzenediol (referred to as Cmϕ2Cm, m = 10, 12, 14, respectively) in aqueous solution using dynamic light scattering, 1H NMR and rheology measurements. The results showed that all three surfactants formed large network-like aggregates at low concentrations. However, C10ϕ2C10 formed small compact micelles simultaneously but neither C12ϕ2C12 nor C14ϕ2C14 did. These network-like aggregates were transformed into the wormlike micelles with increasing the surfactant concentration. The length of alkyl tails was found to strongly affect the viscoelasticity of wormlike micellar solutions. From C10ϕ2C10, C12ϕ2C12 to C14ϕ2C14 in turn, the system developed rapidly from the viscous fluid to typically viscoelastic solution and then to a solid-like gel. The scaling exponents of the concentration dependence of both zero-shear viscosity (η0) and plateau elastic modulus (G′∞) greatly exceeded the theoretic predictions, showing fast micellar growth and strong entanglements between the wormlike micelles. For C14ϕ2C14 that had the longest alkyl tails in this series, the wormlike micelles formed at 140 mmol L−1 were quite long and the micellar reptation dominated over the scission and recombination. This system yielded a viscosity as high as 2.20 × 104 Pa⋅s at 25 °C.
The viscoelastic wormlike micellar solutions formed by the carboxylate gemini surfactant, O,O′-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C12ϕ2C12), have been investigated by steady-state and dynamic frequency-sweep rheological techniques. Another system using its homologue, O,O′-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C12ϕC12), was also examined for comparison. Both C12ϕ2C12 and C12ϕC12 formed wormlike micelles without any additives. The C* corresponding to the onset of the semi-dilute regime was 48 mmol L−1 for C12ϕ2C12 and 160 mmol L−1 for C12ϕC12, respectively, showing the considerably high ability and efficiency of C12ϕ2C12 in forming wormlike micelles. The wormlike micelles started to entangle with each other at 60 mmol L−1 for C12ϕ2C12 and 300 mmol L−1 for C12ϕC12. The average length of the C12ϕ2C12 wormlike micelles was estimated to be about 1.0–1.9 μm, significantly longer than the C12ϕC12 ones. The solution viscosity of C12ϕ2C12 at 200 mmol L−1 reached 613 Pa s, much higher than 24.2 Pa s for C12ϕC12 at 500 mmol L−1. The mechanisms of forming wormlike micelles in both cases were revealed by dynamic light scattering measurements. Differently from the normal micellar growth that C12ϕC12 displayed, C12ϕ2C12 was found to form large network-like aggregates at very low concentrations. These aggregates could more conveniently transform into threadlike (wormlike) micelles by continuously increasing the concentration of C12ϕ2C12, from which a new approach was realised for highly viscoelastic anionic wormlike micellar solutions.
Wettability of aluminum substrate by the aqueous solutions containing ethoxylated alcohol nonionic surfactants C12En- or Triton X-series was studied using dynamic contact angle measurements. The efficiency of wetting was found to strongly depend on the length of polyoxyethylene (POE) chain of C12En- or Triton X surfactants. For C12E4 that has a very short POE chain, it hardly made the aqueous solution spreading over aluminum. The others with a long POE chain were indeed very efficient in promoting the solution spreading. Moreover, all the spreading process could be completed within 10 s. The single-layer NiAl2O3 coatings were fabricated from the precursor solutions containing C12En- or Triton X surfactants and the reflectance spectra were measured by a UV/vis spectrophotometer equipped with an integrating sphere. The results indicated that the precursor solution with a long POE chain surfactant as wetting agent favored to fabricate a uniform film on the aluminum substrate and therefore to get a high solar absorptance.
Colloid and Polymer Science 2013 Volume 291( Issue 6) pp:1471-1478
Publication Date(Web):2013 June
DOI:10.1007/s00396-012-2883-8
The mixed adsorption of a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (abbreviated as 12-2-12), and an anionic conventional surfactant, sodium dodecyl sulfate (SDS), was examined using surface tension measurements. The viscoelastic properties of the mixed films were investigated by dilational interfacial rheology technique. The results showed that the addition of SDS promoted the close packing of adsorbed molecules at the interface, which increased the dilational elasticity of the mixed films. The stability of the foams was determined by the half-life of foam height collapse. The foams generated by 12-2-12/SDS mixtures were more stable than that formed by pure 12-2-12. In the presence of sodium bromide, the foam stability was further enhanced and the surfactant concentration required to attain the maximum effect in stabilizing foams was greatly reduced. The high foam stability could well relate to the high elasticity of the film.
A new gemini surfactant with a long and rigid spacer, O,O′-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C12ϕ2C12), has been synthesized. Its aggregation in aqueous solution has been studied using static and dynamic light scattering measurements. The homologue O,O′-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C12ϕC12) whose spacer only contains a single phenyl group was also examined for comparison. Dynamic light scattering (DLS) revealed the unexpected existence of large aggregates in the solution of C12ϕ2C12. However, C12ϕC12 showed rather normal aggregation behavior. Both the results of intrinsic viscosity and light scattering demonstrated a loose structure for the large aggregates of C12ϕ2C12. This behavior was attributed to an extending configuration of C12ϕ2C12 with the two alkyl tails stretching toward the solution due to the rigidity of the long spacer. The large network-like aggregate formation was an inevitable outcome of spontaneously reducing the energy of the system. Freeze-fracture transmission electron microscopy (FF-TEM) images and 1H NMR measurements supported this speculation. Due to the columnar-like molecular geometry, the large network-like aggregates were directly transformed into rodlike micelles with increasing surfactant concentration. Depending on further micellar growth, the wormlike micelles were finally formed as confirmed by rheological measurements.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2012 Volume 396() pp:258-263
Publication Date(Web):20 February 2012
DOI:10.1016/j.colsurfa.2012.01.004
The influence of the bolaform salts in aqueous subphase, ethanediyl-α,ω-bis(ethyldimethylammonium bromide) (Bola2Et), alkanediyl-α,ω-bis(methyl dimethylammonium bromide) (Bolan, n = 4, 6, 8) and alkanediyl-α,ω-bis(benzyldimethyl ammonium bromide) (Bolanph, n = 2, 4, 6, 8), on the monolayer behavior of sodium hexadecyl sulfate (SHS) has been studied by Langmuir film balance technique. The NMR measurements revealed the benzene rings of these counterions were penetrated among the headgroups of SHS except Bola2ph. This made the interaction of Bolanph with SHS stronger than that of Bolan. With increasing n of both Bolan and Bolanph from 4 to 6, the limiting molecular area (AE) monotonously increased. For Bola8ph, the long spacer chain was bent toward the alkyl tails of SHS, which made the AE reduced under the strong interaction of both. All these suggested that the monolayer behavior of SHS could be controlled by the bolaform counterions in aqueous subphase.Graphical abstractThe Langmuir monolayer behavior of SHS can be well regulated by the bolaform salts with different spacer lengths.Highlights► Bolaform counterions in aqueous subphase can effectively control the Langmuir monolayer behavior of SHS. ► The spacer length of counterions dominates the behavior of SHS monolayer. ► The bolaform conterions attached by benzene rings yield strong interaction with SHS in monolayer.
Journal of Colloid and Interface Science 2011 Volume 356(Issue 1) pp:176-181
Publication Date(Web):1 April 2011
DOI:10.1016/j.jcis.2010.12.065
The formation and the properties of wormlike micelles in aqueous solutions of mixed cationic and anionic gemini surfactants, 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3(OH)-12) and O,O′-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C12ϕC12), have been studied by steady-state and dynamic rheological measurements at 25 °C. With the addition of a small amount of C12ϕC12 into the solution of 12-3(OH)-12, the total surfactant concentration of which was always kept at 80 mmol L−1, the solution viscosity was strongly enhanced and its maximum was much larger than that of the mixed system of propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (12-3-12) and C12ϕC12. The results of dynamic rheology measurements showed that 12-3(OH)-12/C12ϕC12 formed longer wormlike micelles in comparison with 12-3-12/C12ϕC12. This was attributed to the effect of hydrogen bonding occurring between 12-3(OH)-12 molecules, which was an effective driving force promoting micellar growth. As few C12ϕC12 participated in the micelles, the electrostatic attraction between the oppositely charged head groups of 12-3(OH)-12 and C12ϕC12 made the molecules in the aggregates pack more tightly. This reinforced the hydrogen-bonding interactions and greatly promoted the micellar growth.Graphical abstractOn the addition of a small amount of C12ϕC12, the hydrogen-bonding interaction between 12-3(OH)-12 molecules is greatly enhanced, resulting in longer micelles and a viscous solution.Research highlights► Wormlike micelle formed in aqueous solutions of mixed gemini surfactants. ► Intermolecular hydrogen-bonding interaction promotes growth of the wormlike micelles. ► Electrostatic attraction reinforces hydrogen-bonding interactions.
Chinese Journal of Chemistry 2011 Volume 29( Issue 10) pp:2003-2006
Publication Date(Web):
DOI:10.1002/cjoc.201180348
Abstract
The rheological behavior of the aqueous solutions of mixed sulfate gemini surfactant with no spacer group, referred to as d-C12S, and dodecyltrimethylammonium bromide (C12TABr) at a total concentration of 100 mmol·L−1 but different molar ratios of C12TABr to d-C12S (α1) was investigated using steady rate and frequency sweep measurements. The wormlike micelles were formed over a narrow α1 range of 0.20–0.27. The viscoelastic solutions exhibited Maxwell fluid behavior. At the optimum molar ratio of 0.25, the zero-shear viscosity was as high as 600 Pa·s and the length of the mixed wormlike micelle was about 0.45–0.85 µm. The present result provides an example to construct long wormlike micelles by anionic gemini surfactant.
Co-reporter:Yi You, Xiaona Wu, Jianxi Zhao, Yizhang Ye, Wensheng Zou
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2011 Volume 384(1–3) pp:164-171
Publication Date(Web):5 July 2011
DOI:10.1016/j.colsurfa.2011.03.050
This paper reports the investigation about the effect of the alkyl tail length of quaternary gemini surfactants, 2-hydroxyl-propanediyl-α,ω-bis(dimethylalkylammonium bromide), referred to as m-3(OH)-m, where m represents the number of carbon atoms at each alkyl tail, on the foamability and foam stability. To understand the foaming behavior, the adsorption of surfactants at the air/water interface as well as the dilational viscoelasticity of their films was studied using surface tension and dilational interfacial rheology measurements. 14-3(OH)-14 was found to have stronger foamability and stabilize more efficiently the foam than 12-3(OH)-12, however, 16-3(OH)-16 failed to generate foam. The latter was attributed to the self-coiling of the long hexadecyl tails prior to the adsorption of surfactant at the air/water interface, resulting in the ageing effect of the adsorption behavior. For both 12-3(OH)-12 and 14-3(OH)-14, the results revealed a good correlation between the high limit interfacial elasticity and high stability of foam at the level of identical surface excesses.Graphical abstract. Increase in the length of alkyl tails of gemini surfactant generally favors to stabilize the foam but too long tails may self-coil to fail in foaming.Highlights► 14-3(OH)-14 is excellent foam inducing agent and stabilizer. ► 16-3(OH)-16 fails to generate foam due to the self-coiling of hexadecyl tails. ► Foam stability can be well correlated with the dilational interface elasticity.
Colloid and Polymer Science 2011 Volume 289( Issue 9) pp:1025-1034
Publication Date(Web):2011 June
DOI:10.1007/s00396-011-2425-9
This paper reports the adsorption and interfacial viscoelasticity of gemini surfactants with a hydroxyl-substituted spacer, 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide), 2-hydroxyl-butanediyl-α,ω-bis(dimethyldodecylammonium bromide), and 2,3-hydroxyl-butanediyl-α,ω-bis(dimethyldodecylammonium bromide), referred to as 12-3(OH)-12, 12-4(OH)-12, and 12-4(OH)2-12, respectively, at the air/water interface using dropping shape and interface dilational rheology measurements. For comparison, the unsubstituted surfactants were also examined at identical conditions. The results showed that substituted surfactants produced a remarkably higher interfacial elasticity than the corresponding unsubstituted ones. This was attributed to the effect of the intermolecular hydrogen bonding occurring between the hydroxyl-substituted spacers of adsorbed molecules, which resulted in tighter packing of the molecules in the monolayer. Besides, we measured foam stability. The foam produced by the substituted geminis was found to have higher stability than that by the unsubstituted geminis. It was suggested that the foam stability may be related to the limit elasticity of interfacial film at the level of identical surface excesses.
Dyes and Pigments 2010 Volume 84(Issue 3) pp:223-228
Publication Date(Web):March 2010
DOI:10.1016/j.dyepig.2009.09.006
Nile red (phenoxazone-9) was used as a fluorescence probe to detect the sphere-to-rod-to-wormlike micellar transition in the aqueous mixtures of cetyltrimethylammonium bromide and sodium salicylate or potassium bromide, and also in the aqueous solution of a Gemini surfactant, ethanediyl-α,ω-bis(dimethyl dodecyl ammonium bromide). The results showed the Ia/Ib of Nile red (the fluorescence intensity ratio of the twisted intramolecular charge transfer band to the planar locally excited band) was a more sensitive index than the Ia (the fluorescence intensity of the twisted intramolecular charge transfer band) to represent the micellar transition. This was attributed to the special molecular structure of Nile red that has a large conjugated ring and the can form hydrogen bond with water molecules at the electron acceptor group. This led to sensitive response of the twisted intramolecular charge transfer state of Nile red to the change of microenvironment.
Co-reporter:Xiaomei Pei, Yi You, Jianxi Zhao, Yongshu Deng, Erjun Li, Zhenxiang Li
Journal of Colloid and Interface Science 2010 Volume 351(Issue 2) pp:457-465
Publication Date(Web):15 November 2010
DOI:10.1016/j.jcis.2010.07.076
The adsorption and aggregation of 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecyl ammonium bromide) (abbreviated as 12-3(OH)-12) in aqueous solution have been investigated by equilibrium and dynamic surface tension, surface dilational rheology, conductivity, fluorescence probing, viscosity, zeta potential and dynamic light scattering measurements. The results measured by dynamic surface tension, molar and differential conductivities strongly suggested the formation of dimolecular moieties in dilute systems prior to their adsorption and aggregation, which was attributed to intermolecular hydrogen-bonding between the hydroxyl substituted spacers. This increased the hydrophobicity of the molecular moieties and greatly promoted their adsorption at the air/water interface and association in solution. The intermolecular hydrogen-bonding between the molecules adsorbed at the air/water interface made their arrangement tighter and thus produced lower γcmc compared with unsubstituted 12-3-12. Moreover, the effect of intermolecular hydrogen bonding promotes growth of 12-3(OH)-12 micelles and leads to dissociation of the counterions on the aggregate surfaces.Graphical abstract12-3(OH)-12 forms intermolecular hydrogen bonding through the substituted spacers, which in turn strongly affects adsorption and aggregation.Research highlights► The hydroxyl substituted surfactant forms dimers by intermolecular hydrogen bonding. ► Intermolecular hydrogen bonding enhances adsorption and association of the surfactant. ► Intermolecular hydrogen bonding interaction promotes growth of the micelles. ► Hydrogen bonding leads to dissociation of more counterions on the aggregate surfaces.
Journal of Colloid and Interface Science 2010 Volume 341(Issue 1) pp:94-100
Publication Date(Web):1 January 2010
DOI:10.1016/j.jcis.2009.09.023
A homologue of carboxylate gemini surfactants with an azobenzene spacer and different lengths of the alkyl tails, referred to as Cm(azo)Cm, has been synthesized. All the surfactants formed wormlike micelles at relatively low concentrations without addition of salt. The reason was attributed to the long and rigid characteristic of the azobenzene spacer, which yielded the pseudo volume between the two tails and thus a columnar-like molecular geometry favorable for the formation of wormlike micelles. The results of rheology and FF-TEM measurements showed that the length of the alkyl tails strongly affected the viscoelastic properties of the wormlike micelle solution. With the increase of the alkyl tail length, the solutions evolved from a typically viscous fluid to a strong viscoelastic solution and then to a gel-like state. This was attributed to the different microstates as revealed by scaling law. These solutions behave as polyelectrolyte systems because of their additive-free nature.The solutions of newly synthesized gemini surfactants with an azobenzene spacer show strong chain length-dependent viscoelasticity at relatively low concentrations without any additives.
Chinese Journal of Chemistry 2010 Volume 28( Issue 2) pp:189-192
Publication Date(Web):
DOI:10.1002/cjoc.201090052
Abstract
The Langmuir monolayer of carboxylic methyl ester Gemini surfactants with the azobenzene spacer, referred to as MCm(azo)MCm, was prepared and the π-A isotherms were measured. The result revealed an orientational picture of the azobenzene spacer at the air/water interface. Before irradiation, the planar trans-azobenzene group adopted an approximate configuration parallel to the interface and lay on the air/water interface. After UV-light irradiation, the spacer became the twisted cis-one. Because of the location of the polar headgroups at the air/water interface, the two phenyl rings were also forced to take a near-parallel orientation with the interface to reduce the free energy. As a result, the spacer thin-layer was "thickened", which caused an elevation in collapse pressure.
Colloid and Polymer Science 2010 Volume 288( Issue 6) pp:711-717
Publication Date(Web):2010 April
DOI:10.1007/s00396-010-2200-3
We report a systematic investigation on the mixed micellization of the binary homologues of Gemini surfactant 12-s-12 series that has a flexible polyethylene spacer. The results showed that the micellization behavior deviates from the ideality when the difference of the spacer lengths (Δs) of two components is larger than 6. The obvious synergism between two components occurs in the mixtures of 12-2-12/12-18-12 and 12-4-12/12-18-12. This was attributed to a relatively large difference in the molecular shape of the two components induced by the length and the configuration of the spacer chain, which yielded better steric compensation between two components within a mixed micelle than other mixed systems.
Colloid and Polymer Science 2010 Volume 288( Issue 14-15) pp:1359-1367
Publication Date(Web):2010 October
DOI:10.1007/s00396-010-2265-z
The adsorption and the micellization of a series of cationic Gemini surfactants, alkanediyl-bis(dimethyldodecylammonium bromide), referred as 12-s-12, in the isopropyl myristate (IPM)/aqueous system have been investigated using interfacial tension measurements. These surfactants showed much stronger ability for their adsorption at the IPM/water interface and micellization in the water phase in comparison with the corresponding monomer, C12TABr. The adsorption and micellization behavior of 12-s-12 was found to strongly depend on the length of spacer chain, which was comparable with those studied previously in the air/water system. Compared with the compounds with short spacer chain, the 12-s-12 having a long spacer chain (s ≥ 12) showed complicated behavior for their adsorption and micellization due to the bending of the long spacer chain. Thus, the adsorption process could be divided into two stages. At the beginning stage, the adsorption was diffusion-only controlled and the long spacer chain had a free conformation on the interface. At the second stage, more 12-s-12 molecules crowd into the adsorption layer and forced the long spacer chain to bend strongly in order to make room for the new molecules. This resulted in more and more tight packing of the molecules on the interface and thus a quite large limiting dilational elasticity for 12-16-12 and 12-18-12. The addition of salt greatly promoted the adsorption and micellization of 12-s-12. The present results suggested that the 12-s-12 with s ≥ 12 may be a good emulsifier to construct stable emulsion.
Journal of Surfactants and Detergents 2010 Volume 13( Issue 1) pp:
Publication Date(Web):2010 January
DOI:10.1007/s11743-009-1132-8
The viscosity of aqueous micellar solutions depends on the size and shape of the aggregates and thus can be adjusted by addition of another surfactant interacting with the original component, which alters the geometry of the molecule-pair consisting of two surfactants and influences strongly the size and shape of the mixed micelles. Ethanediyl-α,ω-bis(dimethyl dodecyl ammonium bromide), referred to as C12-2-C12·2Br, forms generally large micelles. Addition of a cationic surfactant (dodecyltrimethylammonium bromide, C12TMABr) or a nonionic surfactant (alkyl polyoxyethylene ether, CmEn), the mixed micelle size is reduced violently since the electrostatic repulsion between the same charged heads of C12-2-C12·2Br and C12TMABr or the steric hindrance of the PEO chain of CmEn in the palisade layers of the mixed micelle, which leads to a decrease in the packing parameter P of the molecule-pair. As a result, the zero-shear viscosity (η0) of the mixed solution reduces rapidly. In contrast, on adding an oppositely charged surfactant, η0 of the mixed solution increases strongly since the P of the molecule-pair increases through electrostatic attraction between the oppositely charged heads. The typical cases occur in the mixtures of the anionic gemini surfactant, O,O′-bis(sodium 2-lauricate)-p-benzenediol C11pPHCNa, and the cationic surfactant C12-2-C12·2Br, C12TMABr or its homologue with a different size of heads.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010 Volume 366(1–3) pp:203-207
Publication Date(Web):20 August 2010
DOI:10.1016/j.colsurfa.2010.06.004
A comparative study of the viscoelastic properties of the wormlike micellar solutions of hexanediyl-α,ω-bis(dimethylcetylammonium bromide), referred to as 16-6-16, and cetyltrimethylammonium bromide (CTAB) in the presence of sodium salicylate (NaSal) has been carried out. In terms of Cates model on Maxwell fluid, the characteristic parameters of both wormlike micelles were revealed and compared. The results were discussed on the basis of their different molecular structures, which leaded to different response of 16-6-16 and CTAB to salt.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010 Volume 369(1–3) pp:34-38
Publication Date(Web):20 October 2010
DOI:10.1016/j.colsurfa.2010.07.027
The adsorption of alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) (referred to as 12-s-12, s = 12, 14 and 16) at the air/water interface in the absence and the presence of 10 mmol L−1 NaBr has been investigated using surface tension measurements. The addition of salt strongly promoted the adsorption of 12-s-12, resulting in the formation of the double layers in the subphase below the main adsorption layer. In the double layers, the alkyl tails of surfactants were wrapped in the two layers of the heads and the long and flexible spacer chains were bent to insert into the alkyl tails. The π–A isotherm and surface dilational elasticity measurements supported this hypothesis. The reason may be due to the high hydrophobicity of the 12-s-12 with a long and flexible spacer chain. With addition of salt, the polarity of the solution environment was increased, which expelled the 12-s-12 from the bulk solution. The 12-s-12 molecules concentrated in the domain close to the interface formed the core–shell structure in order that the hydrocarbon chains could escape from the contact with water.
Journal of Colloid and Interface Science 2009 Volume 333(Issue 2) pp:820-822
Publication Date(Web):15 May 2009
DOI:10.1016/j.jcis.2009.02.030
A new gemini surfactant with an azobenzene group incorporated in the spacer has been synthesized. In water, this new compound forms a photo-responsive fluid, and the properties have been characterized by rheology and freeze-fracture electron microscopy (FF-TEM). UV/Vis irradiation causes a reversible change in zero shear viscosity of about 5 orders of magnitude. The different rheological properties correspond to different aggregation states in solution. A densely entangled network and small discrete micelles are respectively responsible for the high viscosity and the low viscosity state, as revealed by FF-TEM. The simplicity and high photo-efficiency of this single-component system act as a foundation for designing novel stimuli-responsive materials.Rheological properties of aqueous solutions of a novel gemini surfactant containing an azobenzene spacer can be conveniently and reversibly controlled using UV/Vis light irradiation.
Chinese Journal of Chemistry 2009 Volume 27( Issue 3) pp:469-471
Publication Date(Web):
DOI:10.1002/cjoc.200990076
Abstract
In order to understand the special role of the flexible alkylene spacer of gemini surfactant in the self-assembly, three gemini surfactants, alkylene-α,ω-bis(didodecylmethylammonium bromide) that is designated as 2C12-s-2C12· 2Br (s=3, 6, 8), were synthesized. When the spread films of 2C12-s-2C12·2Br on the surface of water were constructed, they form the dense layer of the alkyl tails owing to four dodecyl chains per molecule. This induced the bending of the spacer chain toward the air-side at the s smaller than that of C12-s-C12·2Br adsorbed on the air/water interface owing to the enhanced hydrophobic interaction between the alkyl tails and the spacer chain, where C12-s-C12·2Br has only two alkyl tails per molecule. Conclusively, the enhanced hydrophobic interaction between the alkyl tails and the spacer chain can effectively induce the bending of the latter toward the air-side.
Co-reporter:Binglei Song, Jianxi Zhao, Beixi Wang, Rong Jiang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2009 Volume 352(1–3) pp:24-30
Publication Date(Web):5 December 2009
DOI:10.1016/j.colsurfa.2009.09.044
A homologue of dissymmetric quaternary ammonium Gemini surfactants, hexanediyl-α-(butylazobenzene dimethylammonium)-ω-(alkyldimethylammonium) dibromides (referred to as a4-6-m, m = 12, 14, 16), and a symmetric quaternary ammonium Gemini surfactant, hexanediyl-α,ω-bis(butylazobenzene dimethylammonium bromide) (referred to as a4-6-4a), have been synthesized. The Krafft temperature at 1 wt% concentration was determined to be 17–32 °C for dissymmetric a4-6-m homologues depending on the length of aliphatic tail and 42.5 °C for symmetric a4-6-4a. After UV light irradiation, the content of their cis-azobenzene isomers reaching photostationary state was estimated to be ca. 67–71% for the dilution. The critical micelle concentration (cmc) of a4-6-m is close to that of 12-6-m, indicating that the both are equivalent from the self-assembly point of view. But the cmc of a4-6-4a is higher than that of a4-6-12 or 12-6-12, showing the effect of the steric inhibition on aggregation owing to the two rigid terminal azobenzene groups per molecule. After UV light irradiation, the twisted cis-azobenzene groups in both a4-6-m and a4-6-4a molecules shows more obvious steric inhibition, resulting in a larger cmc than that of the trans-surfactants.
Colloid and Polymer Science 2009 Volume 287( Issue 7) pp:839-846
Publication Date(Web):2009 July
DOI:10.1007/s00396-009-2038-8
The effects of NaBr on the adsorption of alkanediyl-bis-(dimethyl dodecyl- ammonium bromide) (referred to as C12-s-C12 2Br) at the air/water interface and on the micellization in the solution have been investigated by surface tension and fluorescence techniques. The results showed that the addition of NaBr greatly enhances their efficiency and effectiveness in surface tension reduction as well as the ability of micellization, even induces strong premicellar aggregation before the cmc. These were attributed to the unique molecular structure of gemini surfactant, where the flexible polymethylene chain was the spacer linking the two quaternary ammonium heads. By a short spacer, the charges of the two quaternary ammonium head groups are concentrated. Even for a long spacer (s = 12), since it is bent toward the alkyl tails, the similar effect is also produced. This results in the high sensitivity of their ionic head groups to salt. Besides, the addition of salt also effectively promotes the hydrophobic interaction between the alkyl tails of gemini surfactants.
Chinese Journal of Chemistry 2008 Volume 26( Issue 4) pp:635-639
Publication Date(Web):
DOI:10.1002/cjoc.200890120
Abstract
Transformation of vesicles formed in DTAB/C11-p-PhCNa aqueous surfactant two-phase (ASTP) was observed by the transmission electron microscopy (TEM). The trans-conformation of the gemini surfactant in the aggregates was considered to be the important factor for constructing the multi-lamellar structure of the vesicle wall. The cation-π interaction between the quaternary ammonium cation and the aromatic ring in the spacer was determined by the UV-Vis spectrum analysis, which, as well as the general electrostatic attraction and hydrophobic force, contributes to the stability of the multi-lamellar structure. The concentrations of the surface-active ions were measured for understanding the mechanism of vesicle transformation. The results show that isoelectric mixing of the two components benefits the growth of vesicles both in size and wall thickness.
A series of double-chain sulfobetain zwitterionic surfactants with varying carbon number of the intercharge group (spacer), (C16H33)2NCH3(CH2)nSO3, where n=2, 3, 4, and 6, referred to as (C16)2NCnS, were synthesized. The influence of the spacer length on the thermal behaviors of (C16)2NCnS in their pure state was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the thermal stability of (C16)2NCnS lowered with increasing the spacer length. All compounds showed a complex polymorphism. Only for (C16)2NC4S and (C16)2NC6S, thermotropic liquid crystals were observed using POM. The former exhibited a smectic A (SmA) phase, whereas the latter formed a hexagonal columnar phase. These liquid crystals obtained both in the cooling and the second heating scans provided compelling evidence for the thermal stability of these compounds.
Journal of Colloid and Interface Science 2007 Volume 310(Issue 1) pp:331-336
Publication Date(Web):1 June 2007
DOI:10.1016/j.jcis.2007.01.056
The interfacial composition and the structure of the water/C12–EOxEOx–C12⋅2Br/n-hexanol/n-heptane microemulsion have been investigated by the dilution method. The results showed that C12–EOxEOx–C12⋅2Br formed a stable water/oil microemulsion with the assistance of n-hexanol. Owing to the relatively large size of the head group, more n-hexanol molecules are populated on the droplet surface than in the C12–2–C12⋅2Br system. The radius of the water pool of the C12–EO3–C12⋅2Br system is not as sensitive to W0W0 as in the C12–2–C12⋅2Br system. Another feature of the present system is that its droplet size is considerably smaller than that of the C12–2–C12⋅2Br system, and also those of the CPC and CTAB systems at relative high water content. This provides a potential application for the synthesis of nanoparticles with small size.C12–EOxEOx–C12⋅2Br forms a stable w/o microemulsion with the assistance of n-hexanol. Owing to the relatively long spacer chain as well as the features of the oxyethylene groups in the spacer, more n-hexanol molecules are required to populate on the droplet surface.
With n-hexanol as the cosurfactant, quaternary ammonium Gemini surfactants C12-EOx-C12 · 2Br (x = 1, 2, 3) formed the reverse micelles in n-heptane. The critical reverse micelle concentrations (cmch) were determined using the absorption spectrum method with iodine as the probe. All values were less than the corresponding critical micelle concentration (cmcaq) in aqueous solution, where C12-EOx-C12 · 2Br formed the normal micelles. The cmch increased with increasing x, which was similar to the variation of cmcaq with x. The saturated amount of water solubilizated by the reverse micelles was enhanced by either increasing x or raising the temperature.
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2007 Volume 304(1–3) pp:25-30
Publication Date(Web):1 September 2007
DOI:10.1016/j.colsurfa.2007.04.017
The micellization of C11pPHCNa, a carboxylated gemini surfactant with an p-Oxybenzene residue in the spacer, in aqueous solution at pH 12 was characterized by the absorption and the fluorescence spectra of the p-Oxybenzene residue. The critical micelle concentration of C11pPHCNa was determined by the absorption spectra to be 0.0940 mmol L−1, which agreed well with that measured by surface tension technique. The fluorescent intensity of C11pPHCNa aqueous solution rapidly increased with increasing C11pPHCNa concentration (C) then reduced when C was beyond 0.45 mmol L−1, which meant the self-quenching occurring. At fixed C, the time-resolved and the steady-state fluorescence quenching with the p-Oxybenzene residue as the intrinsic probe and with methyl viologen (MV2+) as the extrinsic quencher could be used to measure the aggregation number (N) of C11pPHCNa micelle. The results showed the N for the micelle formed at C = 1.5 mmol L−1 was 14.5 and gradually increased with further increasing C. This indicated the more and more molecules packed within a micelle with increasing C, which explained well the fluorescence self-quenching when C was beyond 0.45 mmol L−1.
When a quaternary ammonium surfactant has a suitable solubility in a polar solvent, it can induce the phase self-separation of mutually soluble polar and apolar mixed solvents and a stable interface between the two phases can be formed. This phenomenon is attributed to the quaternary ammonium surfactant reaching suitable solubility in the polar solvent and driving out the most part of the apolar solvent in which the surfactant is insoluble. As a result, phase separation appears. Using aqueous surfactant two-phase as reference, we suggest that it be termed nonaqueous surfactant two-phase and also as two oil phases for short.
