High Concentration Of Cetyltrimethylammonium Bromide Research Articles

Inhibitory action of quaternary ammonium bromide on mild steel and synergistic effect with other halide ions in 0.5 M H2SO4

The corrosion inhibition of mild steel in 0.5M H2SO4 solution has been investigated using electrochemical methods, X-ray diffraction (XRD) and scanning electron microscope (SEM). The adsorption and inhibition action of acid corrosion of mild steel using cetyltrimethylammonium bromide (CTABr) and different halides (NaCl, NaBr and NaI) has shown synergetic effect. The results showed that the protection efficiency (P%) has high values at considerable high concentration of CTABr. However, in the presence of the different halides, the P increases dramatically at low concentration of CTABr. Physisorption was proposed from the the values of ΔGads0. The synergism parameter (Sθ) is found to be greater than unity indicating that the enhanced P% caused by the addition of the halides to the CTABr is due to a co-operative adsorption of both species. Corrosion products phases and surface morphology were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

Kinetics of Cetyltrimethylammonium Bromide Catalysed Oxidation of Cyclopentanone by N-Bromophthalimide in Acidic Medium

Abstract The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulphate (SDS) on the kinetics of oxidation of cyclopentanone by N-bromophthalimide (NBP) was studied iodometrically at 308 K. In addition to the kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties. The kinetic observations indicate fractional order and first order dependence with respect to [cyclopentanone] and [NBP] respectively. Cationic surfactant (CTAB) strongly catalyses the oxidation of Cyclopentanone in aqueous acetic acid medium. Typical kobs and [CTAB] profile were observed i. e. with the progressive increase in [CTAB], the reaction rate increased and at higher concentration of CTAB, constancy in kobs was observed. Anionic surfactant (sodium dodecylsulphate, SDS), mercuric acetate and phthalimide did not influence the reaction rate. The presence of inorganic salts (KCl, KBr) exhibits a severe hike in the reaction rate. The various activation parameters in the presence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed.

OXIDATION BEHAVIOR OF L-THREONINE BY N-BROMOPHTHALIMIDE IN MICELLAR SYSTEM OF CTAB

ABSTRACT The effect of cationic surfactant Cetyltrimethylammonium bromide (CTAB) molecules on the oxidation of L-threonine by N- bromophthalimide (NBP) has been studied at 308 K. The reaction exhibits first order dependence on NBP and fractional positive order on L-threonine and negative fractional order dependence on HClO 4 . The effects of KCl, KBr, phthalimide, mercuric acetate and dielectric constant of the medium have also been studied and summarized. CTAB strongly catalyzes the reaction and after achieving a maximum the rate remains almost constant at higher concentrations of CTAB. This micellar effect has been analyzed, plotted and results are treated quantitatively in terms of Berezin model. The various activation parameters in presence and absence of CTAB have been also evaluated. A suitable mechanism along with rate law consistent with the experimental findings has been worked out. Based on the model association rate constants have been computed. Keywords: Micellar Kinetics, N-bromophthalimide, L-threonine, Oxidation, Berezin model

Compartmentalized Hollow Silica Nanospheres Templated from Nanoemulsions

Nanoemulsions with very high stability can be created by ultrasonication using a rich variety of surfactants, oils, and solution conditions. Multicompartments within a nanoemulsion droplet can also be created via a carefully chosen surfactant system. We will show in this paper that silica templating of a nanoemulsion system results in compartmentalized hollow silica nanospheres (HSN) of sub-100 nm size under neutral pH conditions. The system consists of water, cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate, n-hexadecane, n-octane, and n-hexanol. Two types of HSN can be obtained by manipulating the formulation; one is named single-compartment HSN (SC-HSN), where the HSN encapsulate a single water-in-oil droplet; the other is multiple-compartment HSN (MC-HSN), where the HSN encapsulate multiple smaller HSN. Using a high concentration of CTAB, we obtained a transparent solution of narrow size-distributed ultrasmall HSN (US-HSN) with a diameter of 12 nm. Parameters involved in the nanoemulsion have been examined and a possible mechanism is proposed. We show further that various new types of nested interior structures within HSN could be created by using other block copolymer type surfactants. Changing the oils to various food oils can also lead to biocompatible multicompartmentalized hollow silica nanospheres. A potential application of SC-HSN as a codelivery system of hydrophilic and hydrophobic drugs was demonstrated in simulated body fluid (SBF) using oil-soluble and water-soluble dyes as model compounds. Finally, we consider the mechanism responsible for the rich varieties of the nested structure in HSN and discuss factors promoting the stability of the nanoemulsion system for easy templating with ultrason-induced sol–gel silica chemistry.

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20–30nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous–macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.

Investigation of Phase Separation Behavior and Formation of Plasmonic Nanocomposites from Polypeptide-Gold Nanorod Nanoassemblies

Genetically engineered elastin-like polypeptides (ELP) can be interfaced with cetyltrimethyl ammonium bromide (CTAB)-stabilized gold nanorods (GNRs) resulting in the formation of stable dispersions (nanoassemblies). Increasing the dispersion temperature beyond the ELP transition temperature results in phase separation and formation of solid-phase ELP-GNR matrices (nanocomposites). Here, we investigated different physicochemical conditions that influence nanocomposite formation from temperature-induced phase separation of ELP-GNR nanoassemblies. The presence of cetyltrimethyl ammonium bromide (CTAB), used to template the formation of gold nanorods, plays a significant role in the phase separation behavior, with high concentrations of the surfactant leading to dramatic enhancements in ELP transition temperature. Nanocomposites could be generated at 37 °C in the presence of low CTAB concentrations (<1.5 mM); higher concentrations of CTAB necessitated higher temperatures (60 °C) due to elevated transition temperatures. The concentration of gold nanorods, however, had minimal influence on the phase separation behavior and nanocomposite formation. Further analysis of the kinetics of nanocomposite formation using a mathematical model indicated that CTAB largely influenced the early event of coacervation of ELP-GNR nanoassemblies leading to nanocomposites, but had minimal effect on nanocomposite maturation, which is a later-stage longer event. Finally, nanocomposites prepared in the presence of low CTAB concentrations demonstrated a superior photothermal response following laser irradiation compared to those generated using higher CTAB concentrations. Our results on understanding the formation of plasmonic/photothermal ELP-GNR nanocomposites have significant implications for tissue engineering, regenerative medicine, and drug delivery.

Precipitation, stabilization and molecular modeling of ZnS nanoparticles in the presence of cetyltrimethylammonium bromide

ZnS nanoparticles were precipitated in aqueous dispersions of cationic surfactant cetyltrimethylammonium bromide (CTAB). The sphere radii of ZnS nanoparticles calculated by using band-gap energies steeply decreased from 4.5nm to 2.2nm within CTAB concentrations of 0.4–1.5mmolL−1. Above the concentration of 1.5mmolL−1, the radii were stabilized at R=2.0nm and increased up to R=2.5nm after 24h. The hydrodynamic diameters of CTAB–ZnS structures observed by the dynamic light scattering (DLS) method ranged from 130nm to 23nm depending on CTAB concentrations of 0.5–1.5mmolL−1. The complex structures were observed by transmission electron microscopy (TEM). At the higher CTAB concentrations, ZnS nanoparticles were surrounded by CTA+ bilayers forming positively charged micelles with the diameter of 10nm. The positive zeta-potentials of the micelles and their agglomerates were from 16mV to 33mV.Wurtzite and sphalerite nanoparticles with R=2.0nm and 2.5nm covered by CTA+ were modeled with and without water. Calculated sublimation energies confirmed that a bilayer arrangement of CTA+ on the ZnS nanoparticles was preferred to a monolayer.

Effect of CTAB Micelle on the Oxidation of L-Leucine by N-Bromophthalimide: a Kinetic Study

Abstract The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) on the oxidation of L-leucine by N-bromophthalimide (NBP) has been studied at 308 K. The reaction exhibits first order dependence on NBP and L-leucine and negative and fractional order dependence on HClO4. The effects of KCl, KBr, phthalimide and mercuric acetate have also been studied and summarized. The rate of reaction increased with an increase in dielectric constant of the medium. CTAB strongly catalyzes the reaction and typical k obs and CTAB profile was observed, i.e., with a progressive increase in CTAB, the reaction rate increased and after achieving a peak k obs decreased at higher concentrations of CTAB. The results are treated quantitatively in terms of “Piszkiewicz” and “Raghvan and Srinivasan's” models. The various activation parameters in presence and absence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed. The rate constant in micellar phase k M, cooperativity index (n), binding constant (K 1 and K 2) have been computed.

Controllable Synthesis of NIR-Luminescent ErQ3 Nano-/Microstructures through Self-assembly Growth

The NIR-luminescent ErQ3 nano-/microstructures have been successfully synthesized through a simple microemulsion route. Various morphologies, including nanorods, bundles, and urchins, have been achieved by tuning the fundamental experimental parameters, such as the organic solvents and the concentration of cetyltrimethylammonium bromide (CTAB). The results from SEM images indicate that a solvent with lower polar and higher boiling-point would result in nanorods, while higher concentrations of CTAB and solvents with higher polar and lower boiling-point would prefer the formation of bundles or urchins. The molecular formula of the products being ErQ3 can be deduced by the elemental analysis and thermal gravimetric analysis (TGA) and can be further confirmed by the X-ray powder diffraction (XRD) and Fourier-transform infrared spectra (FTIR). A self-assembly growth mechanism has been proposed to explain our system based on the obtained results. Following excitation of the absorption of the ligand, all the ErQ...

Electrodeposition of Ni-Co-Fe2O3 composite coatings

Ni-Co-Fe2O3 composite coatings were electrodeposited using cetyltrimethylammonium bromide (CTAB)-modified Watt’s nickel bath with Fe2O3 particles dispersed in it. The effects of the plating parameters on the chemical composition, structural and morphological characteristics of the electrodeposited Ni-Co-Fe2O3 composite coatings were investigated by energy dispersive X-ray (EDS) spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results reveal that Fe2O3 particles can be codeposited in the Ni-Co matrix. The codeposition of Fe2O3 particles with Ni-Co is favoured at high Fe2O3 particle concentration and medium stirring, and the deposition of Co is favoured at high concentration of CTAB. Moreover, the study of the textural perfection of the deposits reveals that the presence of particles leads to the worsening of the quality of the observed 〈220〉 preferred orientation. Composites with high concentration of embedded particles exhibit a preferred crystal orientation of 〈111〉. The more the embedded Fe2O3 particles in the metallic matrix, the smaller the sizes of the crystallite for the composite deposits.

Influence of Ionic Strength and Surfactant Concentration on Electrostatic Surfacial Assembly of Cetyltrimethylammonium Bromide-Capped Gold Nanorods on Fully Immersed Glass

The effect of ionic strength as well as surfactant concentration on the surface assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanorods (GNRs) has been studied. Glass substrates were modified to yield a net negative charge through electrostatic coating of polystyrenesulfonate (PSS) over a self-assembled monolayer (SAM) of positively charged aminopropyltriethoxysilane (APTS). The substrates were then fully immersed in GNR solutions at different CTAB concentrations and ionic strengths. Under slightly excess CTAB concentrations, it was observed that the density of GNRs immobilized on a substrate was predictably tunable through the adjustment of NaCl concentration over a wide range. Motivated by the experimental observation, we hypothesize that electrostatic shielding of charges around the GNRs affects the density of GNR immobilization. This model ultimately explains that at moderate to high CTAB concentrations a second electrostatic shielding effect contributed by excess CTAB molecules occurs, resulting in a parabolic trend of nanorod surface density when ionic strength is continually increased. In contrast, at a low CTAB concentration, the effect of ionic strength becomes much less significant due to insufficient CTAB molecules to provide for the second electrostatic shielding effect. The tunability of electrostatic-based surface assembly of GNRs enables the attainment of a dense surface assembly of nanorods without significant removal of CTAB or any other substituted stabilizing agent, both of which could compromise the stability and morphology of GNRs in solution. An additional study performed to investigate the robustness of such electrostatic-based surface assembly also proved its reliability to be used as biosensing platforms.

Multi-technique approach on the effect of surfactant concentrations on the thermal unfolding of rabbit serum albumin: Formation and solubilization of the protein aggregates

Effect of cationic surfactant, cetyltrimethylammonium bromide (CTAB) addition on the thermal denaturation of rabbit serum albumin (RSA) has been studied by employing small-angle neutron scattering (SANS), circular dichroism (CD), intrinsic fluorescence and ultra violet (UV) spectroscopy. The studies were performed at three different temperatures viz., 30, 50 and 70 °C and at two different concentrations of CTAB: the low concentration of CTAB used was 1 mM and the higher concentration was 80 mM (for SANS) and 20 mM (for CD, fluorescence and UV). A collective effect of high temperature and low concentration of CTAB led to the protein aggregation followed by solubilization of these aggregates at higher concentration of surfactant. At 1 mM CTAB and 30 °C, the protein–surfactant complex has a prolate ellipsoidal shape with semi-major axis of 88.9 Å and semi-minor axis of 19.6 Å which are slightly greater than the values of the native RSA. At 50 °C, the size of the semi-major axis increases while at 70 °C an increase in the size of both axes was found. The thermal outcome at higher concentration of CTAB (80 mM) was rather different. Higher concentration of CTAB unfolds the protein by the formation of micelle-like aggregates along the polypeptide chains of the protein and the complex was stabilized at higher temperatures, which was not found with lower concentration of CTAB. The CD results were found to be consistent with the SANS results, i.e., decrease in α-helicity of RSA was more when less amount of surfactant was present as compared to the system with higher surfactant concentration. In a similar fashion, results of relative fluorescence intensity (RFI) reveal that increase in temperature causes decrease in λ max of native RSA as well as RSA + 1 mM CTAB, whereas the λ max remains unchanged for RSA + 20 mM CTAB systems. That means the structure remains compact in presence of 20 mM CTAB while the structure becomes loose when low or zero amount of surfactant was present. The UV results indicate that the protein aggregation takes place in presence of low amount of CTAB and these aggregates become soluble at high concentration of CTAB.

Mesoporous titania–silica composite from sodium silicate and titanium oxychloride. Part II: one-pot co-condensation method

Mesoporous titania–silica composite with large primary particles and homogeneous dispersion of Ti in the silica matrix were synthesized by the sol–gel method via a one-pot co-condensation method using cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. Freshly prepared titanium oxychloride (TiOCl2, titania precursor that is relatively stable) and sodium silicate were used as titania and silica precursors (at the initial ratio of Ti:Si = 1), respectively. The final products were obtained after removing the template by calcination and had overall ratio of Ti:Si = 2:3 (based on EDS and XRF analyses). Other characterization techniques employed include FE-SEM, TEM, FT-IR, DTGA, and nitrogen physisorption studies. The textural properties of the products were highly influenced by the molar concentration of CTAB. Materials with large primary particles (submicrometer-scale dimensions) were obtained at higher concentrations of CTAB (1.7 wt%). The porosities of the templated material were highly reduced compared to that of the untemplated material, emphasizing the influence of Ti loading in the silica matrix. Both pore size and surface area increased at a calcination temperature of 550 °C. The DTGA result showed that the composites exhibited elevated thermal stability (up to 900 °C). In summary, mesoporous titania–silica composite with desirable properties were developed via the proposed method using a relatively inexpensive silica precursor.

Thermo-Induced Aggregation Behavior of Poly(ethylene oxide)-b-poly(N-isopropylacrylamide) Block Copolymers in the Presence of Cationic Surfactants

Low-molecular-weight cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB), were introduced to dilute aqueous solutions of thermosensitive poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAM) block copolymers at concentrations (C(s)) either lower or higher than the critical micelle concentrations (cmc) of the surfactants. The copolymer/surfactant mixtures were investigated by dynamic and static light scattering at different temperatures. At temperature lower than the aggregation temperature (T(agg)), the disaggregation of the copolymers from the loose associations was observed upon addition of the surfactants(.) The thermo-induced aggregation behavior was found to be profoundly influenced with the cooperation of cationic surfactants in terms of T(agg) and the structural characteristics of the aggregates formed at high temperature. In general, T(agg) was increased together with the decrease in the size and molecular weight of the aggregates. These were attributed to the copolymer/surfactant interactions and the electrostatic repulsion coming from the ionic head groups of the surfactants within the mixed aggregates. These changes were much more pronounced at higher C(s). CTAB, which has a longer hydrophobic tail, displayed higher influences compared to DTAB. The formation of vesicles, by one of the copolymers, was suppressed in the presence of CTAB. At the higher CTAB concentration, only small mixed aggregates with very low mass were observed even at the highest temperature investigated.

Template-Assemble Synthesis of ZnO:Er Nanostructure and Their Upconversion Luminescence Properties

ZnO:Er3+ crystallites with controllable morphology of nanorod, columnlike, swordlike, flower-, and prismlike were prepared via the cetyltrimethylammonium bromide (CTAB) assisted hydrothermal process. The effect of the reaction conditions on the morphologies was investigated. A higher concentration of CTAB and/or temperature favor formation of ZnO:Er3+ with larger aspect ratio. When LiOH was used to obtain Zn(OH)4(2-) instead of NaOH, the nanoparticles with smaller aspect ratio was formed due to the different rate determining step. Different solvent also introduced the formation of nanoparticles with different shape as a result of interface-solvent interaction. The different upconversion photoluminescence was observed in different morphology samples under infrared 980 nm excitation, which is causes the variation of the Er3+ local structure.

PH Controlled Synthesis of High Aspect-Ratio Gold Nanorods

Here we report the two-step synthesis of high aspect-ratio gold nanorods via combining low pH growth and higher cetyltrimethylammonium bromide concentration. The approach is motivated by the "slow growth principle," which has been demonstrated recently as a effective protocol to prepare high aspect-ratio one-dimensional nanostructures. When the pH value of the growth solution gradually decreased, the growth rate of nanorods was significantly decreased and a continuous morphological changing from uniform monodisperse gold nanospheres to extraordinary long gold nanorods occured. By simultaneously decreasing the growth pH and increasing the concentration of cetyltrimethylammonium bromide, the length of gold nanorods could be further elongated to above 2 μm with large aspect-ratio of above 80. This kind of high aspect-ratio gold nanorods could be excellent building blocks for optical or electrical nanodevices in future.

Phase Behavior and Shear Alignment in SWNT‐Surfactant Dispersions

The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.

Hydrothermal Synthesis of Free-Floating Au2S Nanoparticle Superstructures

We describe the formation of gold sulfide (Au2S) nanoparticle superstructures via hydrothermal synthesis approach at 175 °C using HAuCl4 and Na2S reagents and cetyltrimethylammonium bromide (CTAB) surfactant. Uniform 2−4 nm Au2S nanoparticles were found to assemble into a densely packed lamellar phase structure, and the resulting material displays a cross-sheet-like morphology. The sheets are 125−250 nm in length and can be suspended in solution. XRD, TEM, and EDS characterization of the nanoparticle samples confirmed the composition of the nanoparticles as Au2S. Some isolated faceted gold nanoparticles were also observed. XPS data also support the formation of Au2S nanoparticles. UV−vis absorption spectra showed only absorption features from the Au2S nanoparticles, and an indirect band gap value of 1.77 eV was obtained. Sufficiently high concentrations of Na2S and CTAB in the reaction mixture were concluded to be necessary to promote the growth of Au2S nanoparticles, and reduce the production of gold nan...

Luminescent Silicon Nanoparticles Formed in Solution

Here we report the two-step synthesis of high aspect-ratio gold nanorods via combining low pH growth and higher cetyltrimethylammonium bromide concentration. The approach is motivated by the "slow growth principle", which has been demonstrated recently as a effective protocol to prepare high aspect-ratio one-dimensional nanostructures. When the pH value of the growth solution gradually decreased, the growth rate of nanorods was significantly decreased and a continuous morphological changing from uniform monodisperse gold nanospheres to extraordinary long gold nanorods occured. By simultaneously decreasing the growth pH and increasing the concentration of cetyltrimethylammonium bromide, the length of gold nanorods could be further elongated to above 2 microm with large aspect-ratio of above 80. This kind of high aspect-ratio gold nanorods could be excellent building blocks for optical or electrical nanodevices in future.

A new and simple method for rapid extraction and isolation of high‐quality RNA from grape (Vitis vinifera) berries

AbstractBACKGROUND: A fast and easy method to isolate RNA from grape (Vitis vinifera) berries is proposed.RESULTS: The procedure uses high concentrations of cetyltrimethylammonium bromide (CTAB) and includes boric acid with the purpose of increasing the RNA extraction. Eppendorf tubes can be used since the amount of sample and volumes of reagents needed are small. The method is based on genomic DNA digestion with DNase I, which avoids the disadvantages of using LiCl (e.g. possible amplification of rare transcripts and reduction or even suppression of the activity of RNA‐dependent DNA polymerase). The use of DNase reduces the duration of the isolation method to 8 h. The RNA yield (32.9–49.2 µg g−1) and purity indices were satisfactory in all cases.CONCLUSION: Although there is a referenced grape berry method (RNeasy Midi Kit + polyethylene glycol) that is faster than the one proposed, it is 3.7 times more expensive and gives a lower yield. The ability to successfully amplify from the RNA extract was verified by measuring the β‐tubulin and lipoxygenase gene expression. Copyright © 2007 Society of Chemical Industry