Cetyl trimethyl ammonium bromide surfactants

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Surfactants such as cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-lOO) and sodium dodecyl sulphate (SDS) are the most commonly used. CTAB forms large micelles [24-26] with aggregation number 61, cmc 9.2 X 10 M, and a positive micellar Stem layer TX-lOO has aggregation number 139 with neutral OH groups on the Stern layer, and SDS forms negative micelles with cmc 8.3 x 10 M and aggregation number 131. The... 

Schultz and Matijevic (16) prepared nanoparticles of palladium sulfide (PdS) by the continuous double-jet mixing of PdCl2 or Na2(PdCl4) and Na2S. They found that the particle size was 20-30 nm in mean diameter obtained in acidic media (pH = 2-3), but 2-5 nm in alkaline media, probably due to the high equilibrium concentration of sulfide ions S2- by dissociation of H2S and HS in the alkaline media (pH = 10-12). A cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), was found to be useful for stabilizing the small particles prepared in alkaline media. 

Baxendale, Evans and coworkers reported in 1946 that the polymerization of methyl methacrylate (MMA) in aqueous solution was characterized by homogeneous solution kinetics, i.e. where mutual termination of free radicals occurred, in spite of the fact that the polymer precipitated as a separate phase. Increases in the rates of polymerization upon the addition of the surfactant cetyl trimethyl ammonium bromide (CTAB) were attributed to the retardation of the rate of coagulation of particles, which was manifested in a reduction in the effective rate constant for mutual termination,... 

In this area, recent unrelated efforts of the groups of Bhattacharya and Fife toward the development of new aggregate and polymer-based DAAP catalysts deserve mention. Bhattacharya and Snehalatha [22] report the micellar catalysis in mixtures of cetyl trimethyl ammonium bromide (CTAB) with synthetic anionic, cationic, nonionic, and zwitterionic 4,4 -(dialkylamino)pyridine functional surfactant systems, lb-c and 2a-b. Mixed micelles of these functional surfactants in CTAB effectively catalyze cleavage of various alkanoate and phosphotriester substrates. Interestingly these catalysts also conform to the Michaelis-Menten model often used to characterize the efficiency of natural enzymes. These systems also demonstrate superior catalytic activity as compared to the ones previously developed by Katritzky and co-workers (3 and 4). 

In view of the experimental model in the above studies by Jain and Wu [16], the effect of SDS on protein domains cannot be surmised however, similar thermal behavior has been reported for human SC following treatment with the surfactants SDS and cetyl trimethyl ammonium bromide, both of which... 

Eliasson and Ljunger (33) reported that the cationic surfactant cetyl trimethyl-ammonium bromide (CTAB) slowed down the rate of formation of amylopectin crystallites in gelatinized waxy maize starch, as measured by differential scanning calorimetry (DSC). 

As in the case of the concentration dependence of the chemical shift, the H and 13C band shapes of the surfactant resonance peaks are also concentration dependent. Analysis of H NMR band shapes for large aggregates of a cetyl trimethyl ammonium bromide-water system results in a CMC of 1.0 mM this is consistent with the value measured by other methods.57 The H NMR bands of alkyl trimethyl ammonium salicylate and hexadecyl pyridinium salicylate aqueous systems start to broaden at concentrations just above the CMC. The broadening continues up to a concentration above which the band shape is almost constant, as the concentration is further increased.-58 I3C NMR linewidth analysis of sodium octanoate in aqueous solution gives reasonable estimated CMC values.59... 

Fig. 1. 1H chemical-shift dependence on the concentration of surfactants, Triton X-100 (TX-100) and cetyl trimethyl ammonium bromide (CTAB). 

Competitive displacement of spread (3-lactoglobulin from an air-water interface by (a) nonionic and (b) ionic surfactants. The collapse of the protein network is indicated by showing the change in area occupied by the protein at the interface as a function of surface pressure, (a) Data for A-Tween 20 (polyoxyethylene sorbitan monolaurate) and B-Tween 60 (polyoxyethylene sorbitan momostearate). (b) Data for A-cetyl-trimethyl-ammonium bromide (CTAB), B-lyso-phosphatidylcholinelauroyl (LPC-L), and -sodium dodecyl sulphate (SDS). 

AFM images showing the displacement of a spread (3-lactoglobulin protein film from an air-water interface by the progressive addition of surfactant, (a) Displacement with (polyoxyethylene sorbitan monolaurate) Tween 20, surface pressure Tr=22.5mN/m, image size 3.2 X 3.2 jam. (b) Displacement with cetyl-trimethyl-ammonium bromide (CTAB), TT = 22.8 mN/m, image size 1x1 /rm. (c) Displacement with CTAB in the presence of 0.2 M sodium phosphate buffer, pH — 7, ir— 22.8 mN/m. scan size 1x1 /rm. Data are shown at similar surface pressures in order to allow comparison of domain sizes for ionic and nonionic surfactants. 

The location occupied by a solute within a micelle depends upon the structure and hydrophobicity of the solute as well as the charge of both the surfactant and the solute (Mittal K.L., 1977). A solute bearing a charge may associate tightly to an oppositely charged micelle surface, be confined to a region close to the surface, or exist in the bulk phase. A neutral solute may be solubilized within the micelle interior, close to the surface, in the surface, or on the surface. For those solutes with dimensions that are comparable to that of the micelles, a specific micellar location may not exist. However, two operational positions may be defined (a) within the micelle or close the surface and (b) on the surface, in close proximity to the aqueous bulk phase. Thomas J.K. (1980), for example, suggested that several aromatic molecules are solubilized on, or at the surface of cetyl trimethyl ammonium bromide (CTAB) micelles. 

Fig. 1.4. Main types of surfactants a- nonionic on the basis of long-chain alcohol and ethylene oxide, b -anionic represented by sodium dodecyl sulphate, cationic represented by cetyl trimethyl ammonium bromide, d - betain surfactant represented by fatty acid amidopropyl dimethyl ammonio acetate, e - siloxane surfactant represented by N,N,N-trimethyl-3-(1.1.1.3.5.5.5-heptamethyl trisiloxane-3-yl) propylammonium bromide...

For the evaluation of the foamability of a surfactant the bulk concentration is used at which the relative rate of foam collapse is equal to 50% of its formation (cw °). The cw ° values determined from foam formation isotherms of a number of products are given in Table 6.1. As it is seen, typical representatives of anionics (sodium dodecyl sulphate), cationics (cetyl trimethyl ammonium bromide) and nonionics (ethoxylated alkylphenols) give bubble foams at very low concentrations, and the foam stability of ionic surfactants does not differ much from that of nonionics. For anionics, the highest concentrations are required for soaps of higher carboxylic acids. 

Let us now discuss some applications of microemulsions in catalytic processes. It has been shown in [298] that the use of microemulsions instead of organic solvents for electrochemical reactions is advantageous from both economical and ecological reasons. The electrode/fluid interface in microemulsions probably consists of a dynamic layer of surfactant molecules packed more loosely on the electrode than in aqueous solutions. Microemulsions provide good yields of carbon-carbon addition products in reactions catalysed by cobalt complexes when preparing vitamin B 2. Excellent stereo-selective control in microemulsions made with the cationic surfactant cetyl trimethyl ammonium bromide was demonstrated for the catalytic cyclisation of 2-(4-bromobutyl)-2-cycIohexene-l-one to 1-decalone. Electrochemical synthesis may be a viable future approach to environmentally friendly chemical methods. 

When we have small water pools in a continuous oil phase an emulsion is produced that can be stabilized by the introduction of surfactants such as cetyl trimethyl ammonium bromide. The microemulsions thus produced can serve as nanoreactors for the synthesis of nanorods. The ratio of water to surfactant affects the size of the nanoreactor and this in turn can influence the size and shape of nanorods. Nanorods of oxides, metals, and semiconductors have been synthesized examples include Ce02, BaTiOa, BaCr04, Ag, and CdSe (25). 

---