High Concentration Of Cetyltrimethylammonium Bromide Research Articles

Cyclodextrin as a capturing agent for redundant surfactants on Ag nanoparticle surface in phase transfer process

High-yield phase transfer of hydrophilic mercaptosuccinic acid (MSA)-modified Ag nanoparticles into chloroform is readily attained using cetyltrimethylammonium bromide (CTAB) through electrostatic interaction. Increasing CTAB amount to a certain degree has achieved nearly complete phase transfer due to the sufficient formation of stoichiometric ion-pairs on particle surface. However, at high CTAB concentration, some unbonded CTA + cations will be physically adsorbed on particle surface and enter chloroform layer simultaneously, which cannot be removed by simple water washing or centrifugation. By using β-cyclodextrin (CD) as a capturing agent, this portion of CTA + cations can be adequately removed due to the possible inclusion function of CD. Upon removal of the unbonded CTAB, the monolayer formation of phase-transferred Ag nanoparticles at air–water interface presents improved two-dimensional (2D) orderliness owing to the more effective interdigitation among adjacent particles.

Static secondary ion mass spectrometry for nanoscale analysis: surface characterisation of electrospun nanofibres

The viability of static secondary ion mass spectrometry (S-SIMS) for selected applications of nanoscale analysis has been investigated, focusing on nanofibres produced by electrospinning (ES) as a test case. The samples consist of non-woven nanowebs of which the individual fibres have diameters in the range of 100 nm. Use of solutions with functionalised polymers or polar additives potentially allows the surface composition to be tailored as a function of the application. So far nanowebs are primarily characterised by morphological examination. This paper describes the first detailed characterisation of molecular composition at the surface of nanofibres electrospun from poly(epsilon-caprolactone) (PCL) solutions in acetone containing 0-15 mol% (relative to PCL) of cetyltrimethylammonium bromide (CTAB). Application of S-SIMS to nanowebs has allowed mass spectra to be recorded containing the major diagnostic ions of both components. Their relative intensities point to surface enrichment and depletion of the polar CTAB additive relative to the PCL matrix for samples electrospun from solution containing low and high CTAB concentrations, respectively.

Manipulation of the Electroosmotic Flow in Glass und PMMA Microchips with Respect to Specific Enzymatic Glucose Determinations

The determination of glucose in microfluidic chips made of glass or PMMA was used as a model for the combination of an enzymatic reaction with the separation of compounds. It was based on the enzymatic oxidation of glucose and the amperometric detection of hydrogen peroxide. Real samples frequently contain compounds, such as ascorbic acid, which may interfere with quantitative glucose determinations. Thus, electrophoretic separation of specific from unspecific signals was envisaged by applying electric fields which are also used to control the flow of liquid via electroosmotic effects. Surface charge densities of the capillaries influence the electroosmotic flow (EOF). They are dependent on the chip material and on the adsorption of components from the background electrolyte. Reversal of the EOF after addition of cetyltrimethylammonium bromide (CTAB) and an increase in EOF after addition of sodium dodecylsulfate (SDS) were observed at lower surfactant concentrations with the PMMA chips rather than with the glass chips. For both chip materials these concentrations were below the critical micelle concentration. Effective separation of H2O2 and ascorbic acid was achieved with low CTAB concentrations, which lead to a reduction, but not to a reversal of the EOF. Reversal of the EOF by higher CTAB concentrations or the increase in cathodic EOF by SDS accelerated ascorbic acid transportation and reduced the differences in migration times. Thus, for the specific determination of glucose, glucose oxidase was added together with low CTAB concentrations to the background electrolyte. This avoided interference from ascorbic acid, and data obtained from the analysis of fruit juices showed a good correlation to data obtained from a reference method.

Structural changes in CTAB/H2O mixtures using a rheological approach

A complete, rheometrical analysis (steady, oscillatory and transient stress-relaxation experiments) may be performed to indirectly elucidate the inner structure of surfactant solutions over a wide range of physicochemical conditions. In this paper, structure and structural changes in cetyltrimethylammonium bromide (CTAB)/H2O mixtures have been studied by a set of rheological experiments as a function of composition (2–40 wt% CTAB) and temperature (20–70 °C). This system was chosen for several reasons: firstly, it forms elongated micelles and exhibits a strong viscoelasticity at low concentrations (ca. 2 wt%); secondly, it has a low critical micellar concentration and a Krafft temperature close to the room temperature; third, a nematic phase (type-I, N) is formed in the concentration range 25–29 wt% with a clearing temperature of ca. 40 °C. The nematic phase is intermediate to a micellar isotropic phase (L1), at low concentration, and to a normal hexagonal lyomesophase (H1) at high concentration of CTAB. The L1 phase, consisting of a very large region, exhibited different rheological properties. At 30 °C, viscoelastic data revealed a sphere-to-cylinder transition in shape of micelles in mixtures above 14 wt% CTAB. By increasing further the composition, a fast micellar growth was observed without reaching an entangled phase. The evolution of micellar morphology was also recorded with increasing temperature. The nematic and hexagonal phases, made by similar structural units (i.e. unconnected cylindrical aggregates), behaved like shear thinning materials and showed a comparable viscoelastic spectrum consisting of fast and slow relaxation processes. The slower relaxation times were interpreted as a relaxation of a shear-induced orientation that involved large lyotropic domains. Faster relaxation times (<1 s), on the contrary, could be related to dynamics or kinetics of stiff cylindrical aggregates.

Electrodeposition of particles at nickel electrode surface in a laminar flow cell

Electrodeposition of polystyrene particles on a nickel electrode was observed in the laminar flow cell. The efficiency (rate) of the electrodeposition was determined depending on flow intensity, electrode polarization vs. Ag/AgCl electrode and ionic strength of the solution. The negative polystyrene latex particles were turned positive by adsorption of cetyl trimethyl ammonium bromide (CTAB) and experiments were performed at fixed concentration of the surfactant. It was found that at the CTAB concentration 5×10 −5 mol dm −3 mostly single particles were deposited. It was observed that during the experiment, particles were deposited at a constant rate, which well correlated with the electrode polarization and their zeta potential. When the experiments were performed at various flow conditions in the laminar flow cell, the rate of deposition was found only weakly dependent on the flow intensity. That indicated that the hydrodynamic blocking effects were negligible under conditions encountered in the experiment. It was confirmed by the simulation of the dependence of the hydrodynamic blocking on the shear rate in the simple shear flow. At higher concentration of CTAB 5×10 −4 mol dm −3 and for the electrode polarization of −1.5 V (vs. Ag/AgCl), transient aggregation at the electrode surface was observed. Qualitative aspects of this aggregation are presented. When the electrode polarization was removed the aggregates moved away except the initial ones, which were firmly attached to the surface. The observed phenomena can be explained in terms of clustering of particles by electrokinetic flows.

Foam and wetting films: electrostatic and steric stabilization

Foam films and wetting films on quartz, obtained from aqueous solutions of two different surfactants [cetyltrimethylammonium bromide (CTAB) and PEO–PPO–PEO triblock copolymer (F108)] with NaCl as a background electrolyte, are considered as convenient models to compare the properties of symmetric (free thin liquid films) and asymmetric (thin liquid films on solid substrate) films with the same air/solution interface. Microinterferometric methodology of assessment of foam and wetting films is used to allow precise determination of the film thickness. In the case of CTAB films, experimental data for the potential ϕ 0 of the diffuse electric layer at the solution/air interface and the potential ϕ 1 at the solution/quartz interface are used to analyze the stability of the films studied. A conclusion drawn is that electrostatic interaction forces stabilize both kinds of films studied. It is shown that with increasing CTAB concentration a charge reversal occurs at both the solution/air and solution/quartz interfaces that determines the stability/instability of the foam and wetting films. Concentration ranges where both types of films produce stable (equilibrium) films are found. There are also concentration ranges where the films either rupture or are metastable (quasi-equilibrium). The CTAB concentration ranges, which provide formation of unstable (rupturing and metastable) and stable films, are different for symmetric (foam) and asymmetric (wetting) thin liquid films. It is only at high CTAB concentrations (>2×10 −4 mol dm −3) that both cases render formation of stable equilibrium films. In the case of F108 films, the comparison of foam films and wetting films on quartz indicates film stability that is either electrostatic or steric in origin. On the basis of the effect of electrolyte concentration on film thickness, the transition from electrostatic to steric stabilization is demonstrated for both kinds of films. The critical electrolyte concentration at which this transition occurs is determined. Foam films are found to be always stable (equilibrium). Formation of either unstable (rupturing and metastable) or stable (equilibrium) wetting films on quartz is established depending on the solution composition. The effects are similar for both hydrophilic and hydrophobic quartz surfaces. The results obtained show certain similarity between foam and wetting films. In both cases, electrostatic forces below the critical electrolyte concentration, and above it steric forces govern film stability. Some specific properties of the wetting films are induced by the asymmetric boundary conditions as distinct from symmetric foam films.

CTAB micelles and the hydroformylation of octene with rhodium/TPPTS catalysts: Evidence for the interaction of TPPTS with micelle surfaces

The addition of cetyltrimethylammonium bromide (CTAB) to TPPTS/rhodium hydroformylation catalysts has a complicated effect on reaction activity and selectivity. In water alone as the solvent, high CTAB concentration leads to the formation of emulsions and reaction selectivity drops. In aqueous alcohol solvents selectivity also drops but the effect appears to be due to the solvent composition. Emulsion formation is minimized and initial reaction activity goes through a maximum at a CTAB/TPPTS ratio of 3. NMR studies show that there is a strong interaction of CTAB and TPPTS in water while the interaction in aqueous methanol appears to be nonspecific.

Fluorescence study of chromophore labeled strong polyelectrolyte bound with oppositely charged surfactant

Four strong polyelectrolyte samples of 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide (DMAA) were radically copolymerized with a single label of naphthalene or pyrene, with both labels and without label, containing about 40 mol % AMPS. Fluorescence nonradiative energy transfer (NRET) I Py/I Np, anisotropy r, I 1/I 3 and excimer emission I E/I M of pyrene labels were observed in dilute aqueous solutions with and without cationic surfactant of cetyltrimethylammonium bromide (CTAB). The overlap concentration was determined as 3 g/L from the appearance of intermolecular excimer. The variation of intra- and intermolecular NRET with total polyelectrolyte concentration showed that the charged chains preferentially interpenetrated each other rather than reduce their coil volume as their concentration beyond the overlap threshold. By binding with CTAB, the polyelectrolyte chain became more coiled as known from the reduced viscosity. The intramolecular NRET was dominant when [CTAB]≤4×10–5 M and then the intermolecular NRET occurred at higher CTAB concentrations with hydrophobic aggregation between CTAB tails bound on different polyelectrolyte chains. The CTAB concentration corresponding to the maxima of I Py/I Np just is equal to the AMPS monomer concentration, indicating the formation of 1:1 binding between surfactant and polyelectrolyte in very dilute solutions. Added salt of NaCl up to 0.1 M hardly affected the intramolecular NRET but affected the I Py/I Np value for the intermolecular NRET.

Growth of silica particles in surfactant gel

Abstract Growth of silica particles produced by the hydrolysis of tetraethoxy silane (TEOS) in gels of the cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was investigated by static light scattering and dynamic light scattering measurements. The time evolution of the size of the silica particles was estimated by the static and the dynamic correlation lengths obtained from the two measurements. Both the growth rate and the final size were smaller at higher concentrations of CTAB, indicating that a more confined network exerted a more restrictive effect on the particle growth. The random motion of silica particles was more severely restricted when the particle was larger and the network mesh size was smaller at higher CTAB concentrations. This restriction of movement resulted in the cessation of the growth of silica particles.

Foam and Wetting Films from Aqueous Cetyltrimethylammonium Bromide Solutions: Electrostatic Stability1

Foam films and wetting films on quartz formed from aqueous solutions of cetyltrimethylammonium bromide (CTAB) are investigated in a wide range of surfactant concentrations in the presence of background electrolyte (5 × 10–4 mol dm–3 NaCl). Foam and wetting films are convenient models for the study of symmetric (free thin liquid films) and asymmetric (thin liquid films on solid substrate) films with the same air/solution interface. Microinterferometric methods of assessment of foam and wetting films are used which allow precise determination of the film thickness. Determined are the values of the potential ϕ0 of the diffuse electrical layer at the solution/air interface (applying the method of “equilibrium foam films”) and the potential ϕ1 at the solution/quartz interface (applying the method of capillary electrokinetics). These values are used to analyze the stability of the films studied in terms of the DLVO theory. A conclusion drawn is that both kinds of films studied are stabilized by electrostatic interaction forces. It is shown that with increasing CTAB concentration, a charge reversal occurs at both the solution/air and solution/quartz interfaces which determines the stability/instability conditions of the foam and wetting films. Concentration ranges where both kinds of films produce stable (equilibrium) films are found. There are also concentration ranges where the films either rupture or are metastable (quasi-equilibrium). The CTAB concentration ranges, which provide the formation of unstable (rupturing and metastable) and stable films, are different for symmetric (foam) and asymmetric (wetting) thin liquid films. It is only at high CTAB concentrations (higher that > 2 × 10–4 mol dm–3) that both cases render formation of stable equilibrium films. These studies give direct experimental indications that the electrostatic interactions between identical or different interfaces can differ when the surfactant concentration is varied.

RELATIONSHIP BETWEEN WETTING OF TEFLON BY CETYLTRIMETHYLAMMONIUM BROMIDE SOLUTION AND ADSORPTION

Contact angles for cetyltrimethylammonium bromide (CTAB) solution (θ) and for series of n-alkanes from n-hexane to n-hexadecane on a Teflon surface were measured. In addition, contact angle measurements for water and diiodomethane on Teflon surface covered with CTAB layer were carried out. The results obtained are used for the determination of the amount of CTAB adsorbed at the Teflon/water interface, the surface free energy of Teflon, the interfacial free energy of Teflon/CTAB solution, the standard free energy of adsorption and the standard free energy of micellization. From an adhesion tension plot of γL cos θ vs γL and application of the Gibbs and Young equations it appears that the amount adsorbed to the Teflon/water interface at a high equilibrium concentration of CTAB is close to that adsorbed at the water/air interface, whereas in the range of low concentrations there are considerable differences between adsorption at Teflon/water and water/air interfaces. This is confirmed by data obtained from the plot of Teflon/solution interface free energy against CTAB solution concentration. It is found that the standard free energy of adsorption at the Teflon/water interface can be determined approximately from the interfacial tail of surfactant-water, tail-tail and tail-Teflon tension data. A good agreement between the standard free energy of micellization and free energy of interactions of CTAB ions through water is found. The free energy of interactions between CTAB ions through water is determined on the basis of the surface free energy of CTAB and the ψ potential. © 1997 Elsevier Science Ltd

Biopolymer–Surfactant Interaction 2: Kinetics of Binding of Cetyltrimethylammonium Bromide with Bovine Serum Albumin

Abstract The results of the kinetics of binding of the surfactant cetyltrimethylammonium bromide (CTAB) with bovine serum albumin (BSA) under varied conditions of CTAB concentration, pH, ionic strength and temperature are presented. The kinetic process has been found to be comprised of either two or three stages; the rate constants of the first, second, and third stages follow the general order of k1 &amp;gt;&amp;gt; k2 &amp;gt; k3. The three-stage kinetic process has been observed at higher CTAB concentrations, higher temperature and in presence of the protein denaturant urea. The activation parameters for this three-stage kinetic process have been determined. Most entropies of activation have been found to be negative (a very few are positive) whereas the activation enthalpies and energies are both positive and negative. The enthalpy and entropy for all the kinetic stages in different environmental conditions have been found to compensate each other, whereas the free energy of activation has remained unaffected. A model for the three-stage kinetic process has been proposed.

Studies on the interaction of azo dyes with cationic surfactant (I)

As the cetyltrimethyl ammonium bromide (CTAB) concentration increases to 2×10−4M the absorption maximum of ethyl orange (EO) makes a blue shift from 475nm to 395nm. At higher concentration of CTAB than 2×10−4M the absorption maximum shifts to higher wavelength than 395nm. A new peak at 395nm is shown to result from the mixed micelle due to dye stacking interaction rather than from a change in dye geometry. Because Raman spectra of EO on interaction with varying amount of CTAB are similar to that of EO in water, EO retains trans azo type on interaction with CTAB. There is a change of c.m.c.s of CTAB for the mixed micelle in the presence of salt. The effect of added salt on c.m.c. of CTAB for the mixed micelle is given that the logarithm of the c.m.c. is a linear function of the logarithm of the sum of the c.m.c. and the concentration of added salt.

The effect of buffers and of organic and inorganic cations on the electrokinetic properties of bacteria

Microelectrophoresis of bacteria provides information on the ionogenic groups in the outer portion of their cell wall. Streptococcus faecalis and Escherichia coli had approximately one carboxylic acid group per 2,300 and 1,000 Å 2, respectively, plus a much lower concentration of basic groups. Incubation time, from exponential growth through decline period, affected these values only marginally. The isoelectric point of S. faecalis was at pH = 2.3. Treating S. faecalis with increasing concentrations of cetyltrimethylammonium bromide (CETAB) or one of five acridine salts reduced the zeta potential from about −22 mV to zero as the K + or Na + cations neutralizing the carboxylate ions in the cell wall were replaced by cetyltrimethylammonium or acridinium cations. Subsequent physical sorption of entire CETAB or acridinium salt molecules raised the zeta potential to +20 mV or higher. The effectiveness of the acridine salts to reduce the negative charge of the cell wall increased with their base strength. It was not related to their ability to inhibit bacterial growth. Some acridines and high concentrations of CETAB caused leakage of bacterial nucleic acids. Relatively high acridine concentrations also caused agglutination of S. faecalis, possible via bridging by nucleic acid-acridine complex coacervates. The effectiveness of inorganic salts to reduce and invert the zeta potential ranked the cations in the order thorium ≅ hydrolyzed ferric ⋍ chromic ⋍ cupric > hydrogen > lead > calcium ⋍ potassium ≅ sodium. The order of effectiveness in inhibiting the bacterial growth was thorium > hydrolyzed ferric > cupric. The remaining cations caused no detectable inhibition at concentrations up to 0.003 M.

Electrokinetic Studies of Bacteria II: Effect of Cetyltrimethylammoniurn Bromide on Streptococcus faecalis

Bacteria were treated with different concentrations of cetyltrimethylammonium bromide in solutions of constant ionic strength equal to 0.01 M, buffered at pH values of 3.4 and 7.0. The initial negative ζ-potential of the bacterial cell wall decreased in absolute value as the concentration of cetyltrimethylammonium bromide was increased, reached zero in the vicinity of the CMC, and then became increasingly positive. This is interpreted as chemisorption of the surface-active cation by ion exchange to form cetyltrimethylammonium carboxylate, followed by physical adsorption of the entire cetyltrimethylammonium bromide molecule. Lysis of the bacteria in the presence of relatively high concentrations of cetyltrimethylammonium bromide increased the positive value of the ζ-potential of the cell wall. Cetyltrimethylammonium bromide completely inhibited the growth of Streptococcus faecalis at a concentration which produced only a 10–30% decrease in the absolute value of the ζ-potential. This seems to indicate that the primary site of attack of the compound is probably not the cell wall.

The adsorption of cetyltrimethylammonium bromide by bacteria, its action in releasing cellular constituents and its bactericidal effects.

SUMMARY: The form of the uptake curve of cetyltrimethylammonium bromide (CTAB) by Staphylococcus aureus and Escherichia coli is that of an adsorption isotherm. Tested on six different bacteria, the maximum amounts of CTAB adsorbed showed variations from one organism to another. When ceils of Staphylococcus aureus. Streptococcus faecalis, Escherichia coli or Salmonella pullorum are suspended in water, the ultra-violet spectrum of the supernatant liquid has a maximum absorption at a wave-length of 260 mμ. The height of this maximum is greatly increased when the cells are suspended in CTAB solutions instead of water. Free purines and pyrimidines contribute to this maximum. There is a parallel relationship between the leakage of 260 mμ.-absorbing material, glutamic acid and inorganic phosphorus from two CTAB-treated Gram-positive bacteria, when their release is followed during the initial rapid phase of leakage. There is a similar relationship for Each. coli. although no glutamic acid is released. Release of cell constituents from CTAB-treated Staph. aureus continues slowly for some time after the initial process and is accompanied by a decrease in dry weight of the cells and a gradual change from positive to negative in their Gram-staining reaction. The rate of release of cellular constituents was increased by raising the temperature or by treatment with high concentrations of CTAB. Treatment of suspensions with sufficient CTAB to sterilize them released amounts of cell constituents comparable to those released by placing the cells in boiling water. When smaller amounts of CTAB were used, a quantitative relationship was found between the amount of CTAB present, the proportion of cells killed and the amount of 260 mμ.-absorbing material released.

Electron microscopy of bacteria treated with cetyltrimethylammonium bromide.

SUMMARY: When viewed in the electron microscope, cells of Staphylococcus aureus, Streptococcus faecalis and Escherichia coli changed markedly when suspended in cetyltrimethylammonium bromide (CTAB) solutions instead of distilled water; the cytoplasm contracts away from the cell wall. The proportion of cells showing such contraction, in the case of Esch. coli, can he correlated with the proportion of cells killed by the treatment. High concentrations of CTAB appear to strip off the cell envelopes.