Increasing Cetyltrimethylammonium Bromide Concentration Research Articles

Micro-DSC and Rheological Studies of Interactions between Methylcellulose and Surfactants

The effects of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), on the gelation of methylcellulose (MC) in aqueous solutions have been investigated by micro differential scanning calorimetry (micro DSC) and rheology. Methylcellulose had a weight average molecular weight of 310,000 and a degree of substitution of 1.8. The concentration of MC was kept at 0.5 wt % (0.016 mM) and 1 wt % (0.032 mM), and the concentration of CTAB in the MC solutions was varied from 0 to 0.6 wt % (16.5 mM). Upon heating, a single endothermic peak, which is due to the hydrophobic association and gelation of MC, shifts to lower temperatures with increasing CTAB for CTAB < or = CMC (0.93 mM or 0.034 wt %), and then it shifts to higher temperatures lineally with CTAB for CTAB > CMC. At the same time, the endothermic enthalpy decreases with increasing CTAB concentration. Even though CTAB shows a significant "salt-in" effect on the gelation of MC, it does not affect the pattern of the sol-gel transition as well as the gel strength of MC. At the highest concentration of CTAB, 0.60 wt %, MC is still able to form a gel. At a given ratio of CTAB/MC, the effect of CTAB on MC becomes stronger when the MC concentration is lower. The results for the MC-CTAB system are compared with an ionic surfactant, SDS and the significant differences in affecting the gelation of MC between two surfactants are recognized.

Interactions between Hydrophobically Modified Associating Polyacrylamide and Cationic Surfactant at the Water‐Octane Interface: Interfacial Dilational Viscoelasticity and Relaxation Processes

The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2‐ethylhexyl acrylate (EHA) (<1.0 mol%) with a hydrolyzed degree of about 1.5–2.0% at the octane‐water interfaces were investigated by means of two methods: the interfacial tension response to sinusoidal area variations (oscillating barriers method) and the relaxation of an applied stress (interfacial tension relaxation method) respectively. The influence of cationic surfactant cetyl trimethylammonium bromide (CTAB) on the dilational viscoelastic properties was studied. The results obtained by oscillating barriers method showed that dilational modulus decreased moderately with the increase of CTAB concentration. The results obtained by interfacial tension relaxation measurements showed that two main relaxation processes exist in the interface at 7,000 ppm polymer concentration: one is the fast process involving the exchange of hydrophobic blocks between the proximal region and distal region in the interface; the other is the slow relaxation process involving conformational changes of polymer chain in the interface. By adding CTAB, the slow process changed obviously due to the strong electrostatic interaction between oppositely charged surfactant and hydrolyzed part of polymer chain. Only when the CTAB concentration was close to the “equal charge point,” the associations formed mainly by the hydrophobic interaction like that in SDS/polymer system appeared and the characteristic time of fast process decreased obviously. The information of relaxation processes obtained from interfacial tension relaxation measurements can explain the results from dilational viscoelasticity measurements very well.

Influence of Low Cetyltrimethylammonium Bromide Concentration on the Interactions and Properties of Hemoglobin with Acyclovir

AbstractThe effects of cetyltrimethylammonium bromide (CTAB) on the properties of hemoglobin (Hb) at low CTAB concentration were studied in Hb/acyclovir/CTAB system by the methods of UV‐Vis spectrum, fluorescence, zeta potential, conductivity and negative‐staining transmission electron microscope (TEM). With the increase of CTAB concentration, the UV peak intensity at 276 nm, the intrinsic fluorescence, the zeta potential of Hb and the system conductivity were all enhanced. Hb was easily oxidized to oxyHb and hemichrome. In Hb/acyclovir/CTAB system, CTAB made the UV‐Vis spectrum, fluorescence, conductivity and conformation of Hb tend to be returned to those of the original Hb but the zeta potential not to do so. The UV absorption peak of Hb‐acyclovir complex disappeared, and the tight structure of Hb aroused by acyclovir was refolded. When CTAB concentration was higher than 5×10−5 mol/L, the two absorption peaks at 536 and 576 nm appeared again, and the Hb structure became looser again.

The effect of molecular weight and degree of substitution on the interactions between carboxymethyl cellulose and cetyltrimethylammonium bromide

The behavior of mixtures of carboxymethyl cellulose (CMC) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated in the dilute range at the liquid–air interface by means of surface tension and ellipsometry, and in the bulk solution by conductivity and turbidity measurements. CMC behaves like a polyanion under the experimental conditions (pH ∼ 7.5). The effect of the CMC molecular weight and degree of substitution on the complexation with CTAB was studied. Keeping the CMC concentration constant at 1.0 g/L, we observed three critical concentrations as the CTAB concentration was increased. Only the CMC degree of substitution (DS) exerted influence on the critical concentration values, evidencing the cooperative binding and the electrostatic interaction as the main driving forces for the complex formation. The critical concentration values found at the liquid–air interface are in accordance with those determined in the bulk solution. The co-adsorption of CMC and CTAB was observed at the liquid–air interface, where the molecular packing became denser with increasing CTAB concentration.

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.

The enhancement effect of surfactants on the penetration of lorazepam through rat skin

Lorazepam is an anxiolytic, antidepressant agent, having suitable feature for transdermal delivery. The percutaneous permeation of lorazepam was investigated in rat skin after application of a water:propylene glycol (50:50%v/v). The enhancing effects of various surfactants (sodium lauryl sulfate (SLS), cetyltrimethylammonium bromide (CTAB), benzalkonium chloride or Tween 80) with different concentrations on the permeation of lorazepam were evaluated using Franz diffusion cells fitted with rat skins. Flux, K p, lag time and enhancement ratios (ERs) of lorazepam were measured over 24 h and compared with control sample. Furthermore, lorazepam solubility in presence of surfactants was determined. The in vitro permeation experiments with rat skin revealed that the surfactant enhancers varied in their ability to enhance the flux of lorazepam. The permeation profile of lorazepam in presence of the cationic surfactant, CTAB, reveals that an increase in the concentration of CTAB results in an increase in the flux of lorazepam in comparison with the control. But an increase in concentration of CTAB or benzalkounium chloride from 0.5 to 1% w/w or from 1 to 2.5% w/w resulted in a reduction in ER, respectively. Benzalkonium chloride which possessed the highest lipophilicity (log P=1.9) among cationic surfactants provided the greatest enhancement for lorazepam flux (7.66-fold over control) at 1% w/w of the surfactant. CTAB (log P<1) and sodium lauryl sulphate at a concentration of 5% w/w (the highest concentration) exhibited the greatest increase in flux of lorazepam compared with control (9.82 and 11.30-fold, respectively, over control). This is attributed to the damaging effect of the cationic and anionic surfactants on the skin at higher concentration. The results also showed that the highest ER was obtained in presence of 1% w/w surfactant with the exception of SLS and CTAB. The increase in flux at low enhancer concentrations is normally attributed to the ability of the surfactant molecules to penetrate the skin and increase its permeability. Reduction in the rate of transport of the drug present in enhancer systems beyond 1% w/w is attributed to the ability of the surfactant molecules to form micelles and is normally observed only if interaction between micelle and the drug occurs.

Interaction of cetyltrimethylammonium bromide and poly(2-(acrylamido)-2-methylpropanesulfonic acid) in aqueous solutions determined by excimer fluorescence

The binding interaction of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic poly(2-(acrylamido)-2-methylpropanesulfonic acid) (PAMPS) in dilute aqueous solutions was studied using the excimer fluorescent emission of the cationic probe 1-pyrenemethylamine hydrochloride (PyMeA·HCl). In the absence of CTAB, the saturation binding of PyMeAH+ on PAMPS is about 2.4 AMPS repeat units for one probe cation as determined by the relative emission intensity, IE/IM, of the excimer to monomer. With increasing CTAB concentration, IE/IM firstly increases, reaches a maximum, then decreases to zero. The IE/IM maximum indicates a critical aggregation concentration (cac) of 10−5 mol/l for CTAB in PAMPS solutions. The CTAB concentration at which IE/IM is zero is exactly equal to the PAMPS concentration, indicating that the probe cation is thoroughly excluded from the binding site of PAMPS by the CTAB cation and the equivalent stoichiometric aggregation is formed between CTAB and PAMPS. The blueshift of the excimer emission and the excitation spectra shows that the decrease of IE/IM with increasing CTAB concentration above the cac is caused mainly by the decrease of the static excimer.

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.

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.

Stability and activity of potato acid phosphatase in aqueous surfactant media.

The effect of three different classes of surfactants viz., anionic, cationic and neutral on catalytic activity of potato acid phosphatase (AcPase) was studied. Anionic surfactants bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium dodecyl sulfate (SDS) inhibited AcPase activity completely at 3 mM concentration. The cationic surfactant cetyltrimethylammonium bromide (CTAB), at 3.33 mM enhanced the activity by 20 per cent. Increase in CTAB concentration decreased the activity, so that only 50 per cent was retained at 27 mM concentration. Brij 35, a neutral surfactant also decreased the activity, whereas TritonX-100 had little or no effect. At low CTAB concentration, an increase in Vmax and a decrease in Km was observed and the V/K ratio increased. TritonX-100 enhanced Vmax without changing Km. The V/K ratio was also increased. The UV-difference spectra of AcPase in presence of CTAB showed perturbations. The intensity of intrinsic fluorescence also enhanced in presence of CTAB.

Catalysis of carbaryl hydrolysis in micellar solutions of cetyltrimethylammonium bromide.

Carbaryl hydrolysis was studied in micellar solutions of cetyltrimethylammonium bromide (CTAB) at pH 7.5 The hydrolysis followed first-order kinetics with respect to carbaryl concentration. Above the critical micelle concentration (CMC) the rate of hydrolysis increased with increasing CTAB concentration. A plateau was ultimately reached, at which the rate constant was 30 times the rate constant in an equivalent solution without CTAB. Entropies of activation were calculated to prove that the reaction mechanism did not change in the micellar environment. The binding constant of the micelle for carbaryl and the rate constant in the micellar pseudophase were determined from kinetic data using the pseudophase model. To verify this binding constant, a study of the solubility of carbaryl in CTAB solutions was performed. The results were found to be in very good agreement with those from the kinetic studies.

Electric birefringence and emf measurements on polymer/surfactant complexes

Electromotive force measurements with a surfactant-sensitive electrode and transient electric birefringence measurements have been carried out to study the interaction between the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the neutral copolymer poly (vinyl alcohol-co-vinyl acetate) (PVAA). The results show that binding of CTAB on the polymer starts abruptly at a critical surfactant concentration c 1 far below the c.m.c. of CTAB. The uptake of surfactant ions by the neutral polymer is accompanied by a dramatic increase of the Kerr constant B. With increasing CTAB concentration, the Kerr constant approaches a saturation value which increases linearly with the polymer concentration. The relaxation of the electric birefringence after removal of the electric field had to be fitted with two time constants τ 1 and τ 2. The relaxation times showed, in contrast to the Kerr constants, no significant variation with polymer or surfactant concentration, which implies that no expansion of the macromolecular coil due to binding takes place. It seems that the long relaxation time τ 2 corresponds to the overall rotational motion of the whole macromolecular coil. The critical association concentration c 1 is, in a large polymer concentration range, nearly independent of the polymer concentration. However, c 1 is markedly depressed, as expected, by addition of NaCl. A linear relationship between the logarithm of the critical concentrations c 1 and the c.m.c. and the logarithm of the counter-ion concentration was found with a smaller slope for c 1. It was concluded that in the CTAB concentration range studied two different association processes take place which differ with respect to their cooperativity: a first non- or only slightly cooperative association process after binding starts, followed by a second highly cooperative association process. The nature of the two different processes is discussed.

Micellar interaction and its catalytic role in the polymerization of acrylamide catalyzed by bisulfite

A micellar interaction of cetyltrimethylammonium bromide (CTAB) with sodium bisulfite was observed, which coincided with a pH shift. This shift probably resulted from the formation of a complex that seemed highly susceptible to oxidation. Bisulfite-catalyzed polymerization of acrylamide was thus accelerated by the addition of CTAB to the polymerization system. The rate of acceleration of a CTAB-containing system was nearly three times as high as that of a CTAB-free nonmicellar system at pH = 5.3, which is an optimum for the highest rate for all cases of polymerization. It was observed that there were some salt effects in nonmicellar simple systems with a gradual increase in R p in proportion to the salt concentration. The unique kinetic feature of a CTAB-micellar system, was in sharp contrast, was a slow increase in R p at the CMC region but a sharp increase in R p at [CTAB] ⋍ 8.0 × 10 ṫ M. The R p approached a limiting value with further increase of CTAB concentration.

Adsorption from solutions exhibiting consolute temperatures. II. Adsorption of 2,6-dimethyl pyridine and cetyltrimethylammonium bromide

The paper describes the measurement of adsorption for a three-component solution system onto silica. The aqueous solution of 2,6-dimethyl pyridine (DMP) and cetyltrimethylammonium bromide (CTAB) shows a lower consolute temperature, the value of which increases with increasing CTAB concentration. The isotherms generally show competition between the CTAB and DMP for the available surface. However, at low DMP concentration (less than 0.5 M), both CTAB and DMP show enhanced adsorption at the expense of water. The effect of temperature is much less marked in the three-component system than in the corresponding two-component (DMP/water) system, where large increases in adsorption occur near to the consolute point.