Molar Ratio Of Cetyltrimethylammonium Bromide Research Articles

Alkyl chain length influence of hydrotrope on the pH responsiveness of surfactant aggregates based on dynamic imine bond

• Ionic hydrotropes with different chain length based on imine bond is prepared. • The pH responsiveness of solution by mixing CTAB and hydrotrope is explored. • The mechanism of different pH responsiveness of mixture is analyzed. The combination of pH-responsive hydrotropes and cationic surfactants is a novel way to construct pH-responsive surfactant aggregates. Herein, in order to investigate the chain length influence of hydrotrope on surfactant aggregate, three hydrotropes were formed from p-hydroxybenzaldehyde (HB) and added amine (hexylamine (HA), octylamine (OA), dodecylamine (DA)) respectively based on dynamic imine bonds. Then the surfactant aggregates were constructed by adding cetyltrimethyl ammonium bromide (CTAB). The molar ratio of CTAB: HB: HA/OA/DA was fixed at 100:55:55. The formation of imine bonds was proved by means of 1 H NMR measurement. Rheological measurements, and cryo -TEM were used to explore the pH responsiveness of the surfactant aggregates. The results showed that as pH increased from 6.0 to 12.0, the CTAB/HB/HA system changed from a low viscosity fluid to a viscoelastic fluid, as the CTAB/HB/OA system transformed from aqueous liquid via a transparent gel solution to a turbid fluid. On the other hand, the CTAB/HB/DA system can achieve four state transitions, from a non-viscosity fluid, via a viscoelastic fluid, turbid fluid and finally to a viscoelastic fluid. With the change of pH, the CTAB/HB/HA system turned from spherical to wormlike micelles, while CTAB/HB/OA experienced changes from spherical micelles via wormlike micelles to vesicles. Finally, the CTAB/HB/DA system was the most complex one, which converted from spherical micelles, wormlike micelles via vesicle, into final wormlike micelles. In conclusion, the sensitivity of pH responsiveness among these three systems gradually improved by increasing the chain length of the hydrotrope formed by HB and amine. This can be attributed to the different growth rates of the packing parameter. This work demonstrated the feasibility of constructing pH responsive surfactant aggregates by introducing hydrotropes to cationic surfactants.

Effect of mixed cationic/anionic surfactants on the low-rank coal wettability by an experimental and molecular dynamics simulation

Mixed surfactants consisting of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) demonstrated high floatability of low-rank coal, and the optimal molar ratio of CTAB and SDS was 1:9. The surface and thermodynamic parameters (CMC, γCMC, Γmax, Amin, ΔGm0) obtained from surface measurements indicated higher surface activity and denser molecular arrangement in the mixed CTAB/SDS surfactants than in single CTAB or SDS. The contact angle of the coal sample increased from 38.9° to 73.7°, and the wetting heat of the coal became less negative, which showed a better positive effect on enhancing the contact angle and restricting the hydrophilicity of the coal surface. Molecular dynamics (MD) simulations were carried out to investigate the influence on the wettability of low-rank coal. The results indicated a significant increase in hydrophobicity of the low-rank coal. Furthermore, the combustible recovery was enhanced significantly by up to 47.67%, and the concentrated ash value was increased by up to 3.63%.

Synthesis and Tuning of Hematite (α-Fe2O3) Iron Oxide Nanorods with Magnetism

In recent years, hematite (α-Fe2O3) iron oxide nanorods have attracted the attention of many researchers due to their wide applications in nanobiosensors, lithium batteries and nanomagnetism. In the present work, hematite nanorods with magnetic and optical properties were synthesized in desirable qualities via a fast and low-cost method. Features of these nanorods were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and vibrating sample magnetometry (VSM). Uniform nanorods with a length of between 20 and 30 nm were fabricated in a 0.05:1:3.4 molar ratio of cetyltrimethylammonium bromide (CTAB)/FeCl3/NaOH. The VSM technique showed that the presence of the CTAB as a surfactant agent in 0.1, 0.05 and 0.025 mol L− 1 concentrations can reduce the magnetization of nanorods with an increase in surface layers. The optical absorbance properties of the hematite nanorods demonstrated that the absorption peaks are well tuned in wavelengths of about 250 and 400 nm. The hematite nanorods with the tuned structure in terms of magnetic and optical properties can be proposed as a desirable option in future applications.

Effect of (Si+Al)/CTAB ratio on crystal size of mesoporous ZSM-5 structure over methanol-to-olefin reactions

Mesoporous ZSM-5 catalysts were prepared with different (Si+Al)/CTAB (cetyltrimethylammonium bromide) molar ratios and their applications in methanol-to-olefin (MTO) reactions were studied at various reaction conditions. It was found that methanol conversion and selectivity to light olefins showed a volcano-type dependency on (Si+Al)/CTAB molar ratios. The highest initial methanol conversion and selectivity of light olefins, catalyst stability were obtained over (Si+Al)/CTAB molar ratio of 15 due to its moderate crystal size with hierarchical structure. A higher C3=/C2= ratio was obtained over mesoporous ZSM-5 catalysts, which was ascribed to high Si/Al ratio and low diffusion hindrance of hierarchical structure.

Tailoring the magnetic properties of cobalt-ferrite nanoclusters

In this contribution, we report on the tuning of magnetic properties of cobalt-ferrite nanoclusters. The cobalt-ferrite nanoclusters were synthesized from a two-step approach that consists of the synthesis of cobalt-ferrite nanoparticles in organic media, followed by their dispersion into aqueous dissolution to form an oil-in-water emulsion. These emulsions were prepared at three different concentrations of the cationic surfactant cetyltrimethylammonium bromide (CTAB), in order to control the size and clustering density of the nanoparticles in the nanoclusters. The synthesized samples were characterized by transmission electron microscopy and their related techniques, such as bright-field and Z-contrast imaging, electron diffraction and energy-dispersive X-ray spectrometry; as well as static magnetic measures. The experimental evidence indicates that the size, morphology, and nanoparticles clustering density in the nanoclusters is highly dependent of the cobalt-ferrite:CTAB molar ratio that is used in their synthesis. In addition, due to the clustering of the nanoparticles into the nanoclusters, their magnetic moments are blocked to relax cooperatively. Hence, the magnetic response of the nanoclusters can be tailored by controlling the size and nanoparticles clustering density.

Particle settling in micellar solutions of varying concentration and salt content

The effect of concentration and molar ratio of cetyltrimethylammonium bromide with sodium salicylate (CTAB/NaSal) micellar aqueous solutions on the settling of non-Brownian spheres is determined. The micelles cause shear thinning, which may result in a shear-stress plateau. The measurements were performed in the wide range of Weissenberg numbers showing drag reduction and enhancement. Maximum drag coincides with the minimum relaxation time. For equimolar solutions, a correlation between Weissenberg number and normalized drag correction factor is proposed. The average settling velocity decreases proportionally to the inverse CTAB/NaSal concentration squared and is closely related to the micellar network size. Salt excess in 10 mM CTAB solutions results in an exponential increase in the average velocity. We find steady and unsteady regimes for the particle motion. In equimolar solutions, the frequency decreases with the concentration, whereas the dominant frequency does not change with salt excess, but is associated with the shear-stress oscillations. We show that the unsteady particle motion is related to the rheological time-dependent properties of the micellar solutions.

The microemulsion preparation and high catalytic performance of mesoporous NiO nanorods and nanocubes for toluene combustion

Cubically crystallized mesoporous nickel oxide nanorods and nanocubes were fabricated by using a facile microemulsion strategy with cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) as surfactant. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the combustion of toluene. It was shown that the morphology of the samples strongly depended on the nature of surfactant: when CTAB was used, the product was mesoporous NiO nanorods; when SDS was adopted, mesoporous NiO nanocubes were obtained. The NiO-CTAB-2 sample derived with a Ni2+/CTAB molar ratio of 0.364 displayed the highest surface area (ca. 46m2/g) and the best low-temperature reducibility. A clear correlation of oxygen adspecies concentration or low-temperature reducibility with catalytic performance was observed. The high catalytic activity (T50%=256°C and T90%=278°C at SV=20,000mL/(gh)) for toluene combustion of NiO-CTAB-2 was related to its larger surface area, higher oxygen adspecies concentration, and better low-temperature reducibility.

Preparation of gold nanoparticles by surfactant-promoted reductive reaction without extra reducing agent

Cetyltrimethyl ammonium bromide (CTAB) has been extensively applied in the solution-phase synthesis of many types of colloidal nanoparticles. However, the uses of CTAB were mainly considered as template or capping agents to form controllable shape and protect the product from agglomeration. Here it was discovered that CATB could serve as a very mild reductant to reduce gold salt precursors preparing gold nanoparticles (GNPs) at base environment. CTAB acted as the reducing agent suffering a partial degradation and forming CTA macro radicals. FTIR proved the formation of CCl and/or CBr bond after CTAB degraded. The characterization of synthesized GNPs was examined by UV–Vis spectra, TEM and XRD. Several factors affecting the process of reaction, such as the amount of NaOH, the molar ratio of CTAB and HAuCl4, the reaction temperature, the effect of light and oxygen, and stirring were discussed.

Cationic Polymerization of β-Pinene Using Keggin Phosphotungstates as Catalysts

Polymerization of β-pinene was investigated in the presence of various Keggin phosphotungstates. The experiments show that cetyltrimethylammonium phosphotungstate with molar ratio of cetyltrimethylammonium bromide to phosphotungstatic acid equal to 0.5 indicate efficient catalytic performance for the polymerization of β-pinene. The catalyst was easily removed from reaction mixture by filtration. Therefore, a clean and environmental friendly strategy for synthesis of terpene resin is developed.

Preparation of Mesoporous 1,4‐Phenylene‐silica Nanorings through a Dual‐templating Approach

AbstractMesoporous 1,4‐phenylene‐silica nanorings were prepared using cetyltrimethylammonium bromide (CTAB) and (S)‐2‐methyl‐1‐butanol as a chiral dopant in concentrated aqueous NH3 solutions. Transmission electron microscopy images of the samples indicated that the nanorings were formed by bending nanorods 360°. With increasing the stirring speed or the (S)‐2‐methyl‐1‐butanol/CTAB molar ratio, the morphologies of mesoporous 1,4‐phenylene‐silicas changed from helical nanofibers to nanorings, and then to nano‐saddles. Circular dichroism spectra of these hybrid silicas indicated that they were chiral.

Synthesis of Nanosized Multilayered Silica Vesicles with High Hydrothermal Stability

Nanosized multilayered silica vesicles have been synthesized through a dual-template way by using cetyltrimethylammonium bromide (CTAB) and C3F7O(CFCF3CF2O)2CFCF3 CONH(CH2)3N+(C2H5)2CH3I− (FC-4) as the cotemplates and tetraethyl orthosilicate (TEOS) as the siliceous precursor. According to transmission electron microscopy, X-ray diffraction, and N2 sorption analysis, the formation of the multilayered silica vesicles passed through the route of the normal mesoporous silica spheres (MCM-41) to irregular hexagonal structures with cavities inside MCM-41 spheres and finally to the small-sized multilayered siliceous vesicles with the increase of FC-4/CTAB molar ratio. The possible mechanism of the two kinds of micelles cooperation was discussed. The synthesized silica vesicle spheres were 30−40 nm with a few shells that may facilitate the transport of the molecules. Furthermore, the vesicular structure was also obtained by aging at 150 °C, which maintained high surface area even after hydrothermal treatment in ...

Synthesis and Surface Properties of Silica Spheres with Core Shell Structure by One Convenient Method

Earlier, we have published a paper on the preparation of silica sphere using propanol as cosurfactant. We report here a highly cost‐effective method of preparation of mesoporous silica spheres with core shell structure using sodium silicate as silica precursor, cetyltrimethyl ammonium bromide (CTAB) as surfactant, and methanol as cosurfactant. Thus after removal of the template by dissolutions or/and activation at higher temperature, mesoporous silica spheres with core shell structure were obtained. The products prepared with methanol to CTAB molar ratio 8.5 : 1 were confirmed to give best results. All the spherical products have very large surface area (~589–1044 m2/g), pore volume (~0.98–1.41 cm3/g), and ordered pore structure.

The use of CTAB to improve the crystallinity and dispersibility of ultrafine magnesium hydroxide by hydrothermal route

The high-dispersed lamellar ultrafine magnesium hydroxide was obtained at relatively low hydrothermal temperature in the presence of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). The procedure described in this study is attractive since proper amount of CTAB could promote the dissolution and precipitation of magnesium hydroxide in hydrothermal system, resulting in the well-defined morphology, narrow size distribution and good crystallinity of ultrafine particles. The resultant magnesium hydroxide was characterized by X-ray powder diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), field-emission scanning electron microscopy (FESEM) and laser diffusion analysis. The method led to the production of particles with mean size of 400 nm and a thickness of 60 nm. The optimal conditions of preparation were hydrothermal treatment at 150 °C for 6 h at pH 11 with Mg 2+/CTAB molar ratio of 80.

A New pH and Thermo-Responsive Chiral Hydrogel for Stimulated Release

Chirality of the amphiphile to promote gelation in the given solvent medium is narrated in a new catanionic surfactant mixture from a twin-chiral, twin-tailed surfactant derived from tartaric acid and cetyltrimethylammonium bromide (CTAB). The surfactant bis(decyloxy) succinic acid (BDSA), a chiral Gemini-type surfactant with a rigid spacer, in association with CTAB formed pH and temperature responsive vesicles and hydrogels. Molecular chirality gave rise to supertwisted fibrillar hydrogels at a BDSA:CTAB molar ratio of 1:2 and in 31% water content. The hydrogels from enantiomeric BDSA were reversibly pH and irreversibly temperature responsive at pH<6.2 and at 55 degrees C, respectively, whereas the corresponding sodium succinates formed transparent clear gels reversible to both pH and temperature. The hydrogels were able to entrap and release model dye molecules, Rhodamine B, and Congo red, responding to thermal and pH stimuli. Circular dichroism unraveled the chiro-optical behavior of the assembled fibers, allowing monitoring of aggregation and packing. The presence and the relative configuration of the stereogenic centers in the structure of this low molecular weight gelator have been observed to be critical to form gels. The high curvature Gaussian gel network was modeled based on the chiral elastic membrane approach and the pitch angle of the Gaussian twist was estimated to be 45 degrees.

Shape and Size Control of ZnO Nanostructures via a Simple Solution Route

ZnO nanostructures with different morphologies were synthesized by condensing the Zn(OH)4(2-) precursors under hydrothermal conditions in the presence of a surfactant, cetyltrimethylammonium bromide (CTAB). Shape and size control of ZnO nanostructures was achieved by relatively simple variations of molar ratio of CTAB to Zn(OH)4(2-). With a higher molar ratio, ZnO nanotubes were obtained, whereas with a lower molar ratio, ZnO nanorods were formed; furthermore, with a moderate w value, the coexistence of ZnO nanorods and nanotubes was also observed. The photoluminescence of ZnO nanorods and nanotubes was also investigated.

Mixed Cationic-Nonionic Surfactants Route to MCM-48: Effect of the Nonionic Surfactant on the Structural Properties

Structurally ordered MCM-48 silicas were facilely synthesized using the mixtures of cetyltrimethylammonium bromide (CTAB) and p-Octyl polyethylene glycol phenyl ether (OP-10) as co-templates with low molar ratio of CTAB to silica (0.139:1) and low concentration of mixed surfactants (ca. 5%) and within a wide range of OP-10/CTAB ratio (0.08–0.25). For comparison purpose, the cubic material was also prepared with only CTAB as the structure-directing agent under the same preparation conditions. The products obtained by different templating method were thoroughly characterized by XRD, N2 sorption, TEM, TG-DSC and 29Si MAS NMR. Measurement results from these techniques indicated that the introduction of nonionic OP-10 had significant effect on the structural properties of MCM-48 and the mixed surfactants' route allowed an efficient synthesis and a more condensed product compared to the only cationic CTAB templating protocol. Finally, our preliminary explanation for that why cubic MCM-48 materials could be obtained in this system and structural properties were sensitive to the OP-10/CTAB ratios was discussed in detail.

Synthesis of rod-like mesoporous silica with hexagonal appearance using sodium silicate as precursor

Using sodium silicate as precursor, rod-like mesoporous silica with hexagonal appearance was synthesized by controlling the pH value of a mixed micelles solution of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) during hydrolysis of ethyl acetate. The resulting mesoporous silica was characterized by small angle X-ray diffraction, nitrogen gas adsorption-desorption measurement and scanning electron microscopy. Results showed that the regular rod-like shapes with hexagonal appearance were obtained at a 9:1 molar ratio of CTAB to CTAC, and that the amounts and lengths of the rod-like mesoporous silica particles decreased with decreasing CTAB to CTAC molar ratio. There existed a type IV adsorption isotherm and an H1 hysteresis loop in N2 gas adsorption-desorption curves.

Effect of phenylazoaniline to cetyltrimethyl-ammonium bromide ratio on micellar shape

The purpose of this study was to determine the influence of phenylazoaniline (PAA) on the shape of cetyltrimethylammonium bromide (CTAB) micelles. Change in micellar shape may have an impact on PAA transport characteristics. In a previous publication (Yoon, K.A. and Burgess, D.J., Pharm. Res. 13 (1996) 433), it was reported that the concentration of CTAB is related to the permeability coefficient of PAA in a triphasic system containing mineral oil, water and micellar phases. The diffusion coefficients of PAA in CTAB solutions were calculated from viscosity, dynamic light scattering and dialysis studies, (using U-tube viscometry, a Nicomp particle sizer and side-by-side diffusion cells, respectively) to determine any change in micellar shape with change in CTAB concentration. Diffusion coefficients were estimated from intrinsic viscosity using Simha's relationship (Tanford, C., Physical Chemistry of Macromolecules. Wiley, New Yoirk, 1961). According to the viscosity and dynamic light scattering studies, CTAB micelles change from spheres to rods at a PAA: CTAB molar ratio of 0.468±0.02, whereas this transition occurred at 0.32±0.02, according to the dialysis data. The difference between these data can be explained by the effects of aqueous boundary layer present on either side of the permeating membrane and the membrane adsorption in the dialysis studies. Aqueous boundary layer effects were determined by changing the stirring rate and the membrane adsorption effect was determined by presaturating the membrane. These studies indicate that change in the permeability coefficient of PAA with increase in CTAB concentration in the triphasic system may be due to change in micellar shape.

INTERACTION OF SULFONATED POLYSTYRENE WITH CATIONIC SURFACTANTS IN AQUEOUS SOLUTION

The interaction of sulfonated polystyrene (SPS) with cetyl trimethylammonium bromide (CTAB) and myristyl trimethylammonium bromide (MTAB) in aqueous solution was investigated. It was found that the solution viscosity increases rapidly at the molar ratio of CTAB/-SO3Na = 0.5 or MTAB/-SO3Na = 0.6 (the first viscosity maximum) and CTAB/-SO3Na = ∼1.5 or MTAB/-SO3Na = 2.0 (the second viscosity maximum). Both the first and the second viscosity maxima are related closely with the hydrophobic domains formed in solution, which can be detected using methyl orange as a spectral probe or N,N-dimethylamino flavone as fluorescent probe. In the higher concentration of [SPS], such as >0.05 M (-SO3Na unit), the SPS/CTAB solution converts to gel suddenly at CTAB/-SO3Na = ∼1.5–1.7 region, but with a further addition of CTAB or SPS, the gel collapses quickly. A term “micelle crosslinking” was proposed to explain the conversion of solution/gel and the reversible nature of gel ↔ solution.