Added Sodium Bromide Research Articles

Regular and irregular deswelling of polyacrylate and hyaluronate gels induced by oppositely charged surfactants

The deswelling kinetics of macroscopic polyacrylate (PA) gels in solutions of dodecyltrimethylammonium bromide (C 12TAB) and cetyltrimethylammonium bromide (C 16TAB), with and without added sodium bromide, as well as hyaluronate (HA) gels in solutions of cetylpyridinium chloride (CPC) are investigated. Additional data are also provided by small-angle X-ray scattering and microgel experiments. The purpose is to study the deswelling behavior of (1) regularly deswelling gels, for which the deswelling is successfully described using a core/shell model earlier employed for microgels, and (2) irregularly deswelling gels, where the gel turns into a balloon-like structure with a dense outer layer surrounding a liquid-filled core. For regularly deswelling gels, the deswelling of PA/C 12TAB is found to be controlled by diffusion through both stagnant layer and collapsed surface phase, while for PA/C 16TAB it is found to be controlled mainly by the latter. The difference in deswelling rate between the two is found to correspond to the difference in surfactant diffusion coefficient in the surface phase. Factors found to promote irregular deswelling, described as balloon formation, are rapid surfactant binding, high bromide and surfactant concentration, longer surfactant chain length, and macroscopic gel size. Scattering data indicating a cubic structure for HA/CPC complexes are reported.

Direct Analysis of SANS and SAXS Measurements of Catanionic Surfactant Mixtures by Fourier Transformation

Vesicle and micellar structures formed by mixtures of the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) with and without added sodium bromide (NaBr) have been examined by small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) techniques. The resulting spectra have been evaluated using a Fourier transform/deconvolution technique. Through indirect Fourier transformation of the scattering intensity and subsequent deconvolution of the resulting cross-sectional pair distance distribution function, detailed information of the cross-sectional and interfacial dimensions of the aggregates is obtained. SANS and SAXS show that the vesicle bilayer has a core radius of 9 A and a headgroup region extending an average 9 A more. SANS results for the micelles investigated indicate a core radius of 10−11 A and a headgroup region of 10 A. This analysis, when compared with theoretical calculations from a thermodynamic cell model, indicates that the ...

Electrostatic Effects on the Phase Behavior of Aqueous Cetyltrimethylammonium Bromide and Sodium Octyl Sulfate Mixtures with Added Sodium Bromide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectrostatic Effects on the Phase Behavior of Aqueous Cetyltrimethylammonium Bromide and Sodium Octyl Sulfate Mixtures with Added Sodium BromideLaura L. Brasher, Kathleen L. Herrington, and Eric W. KalerCite this: Langmuir 1995, 11, 11, 4267–4277Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/la00011a017RIGHTS & PERMISSIONSArticle Views744Altmetric-Citations158LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Micellar catalysis of organic reactions. Part 35. Kinetic determination of the critical micelle concentration of cationic micelles in the presence of additives

AbstractThe critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method. This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations. Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic. Conventional methods cannot be applied with confidence to such systems. The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated. It was wound that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC. The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC. The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.

Ultrasonic relaxation and electrochemical measurements on monomer/micelle exchange in dodecylpyridinium bromide solutions containing added sodium bromide

The ultrasonic relaxations associated with the perturbation of the monomer/micelle equilibrium in dodecylpyridinium bromide (DPBr) have been measured in the presence of 10{sup {minus}4} and 10{sup {minus}1} mol dm{sup {minus}3} sodium bromide (NaBr). The emf of a specially constructed dodecylpyridinium cationic surfactant membrane electrode relative to, successively, a bromide ion, sodium ion, and also a liquid junction electrode has been measured, and the monomer concentration of DP{sup +} in the micellar range and the effective degree of micellar dissociation have been evaluated. The combined dynamic and equilibrium data have been used to investigate the kinetics of the monomer/micelle exchange process by using different versions and modifications of the so-called fast relaxation time equation of Aniansson and Wall and also an alternative approach to investigate kinetics - a phenomenological treatment. The scope and limitations of these approaches to derive new micellar parameters are discussed. From the concentration dependence of the amplitude of the ultrasonic relaxation the volume change associated with the monomer/micelle equilibria has been estimated. In addition density measurements and light scattering measurements were taken.

Allylic oxidation of olefins by cobalt (III), manganese(III), and cerium (IV) acetates in acetic acid in the presence of sodium bromide

The effect of added sodium bromide on the allylic oxidation of olefins by cobalt(III), manganese(III), and cerium(IV) acetates has been studied. Sodium bromide strongly accelerated the oxidation of cyclohexene by these oxidants to give cyclohex-2-enyl acetate in good yield. Only one product was obtained in the oxidation of cycloalkenes, but two allylic acetates were obtained in the oxidations of methyl-substituted cyclohexenes, which have two kinds of allylic hydrogen. A mechanism involving hydrogen abstraction from allylic sites by bromine radicals is suggested.

Oxymetallation. Part 18. Extensive rearrangement to a [4.2.1 ] skeleton in the bromodemercuriation of 2-bromomercurio-9-oxabicyclo[3.3.1]nonane

The distributions of isomeric 2-bromo-9-oxabicyclononanes obtained by the brominolysis of trans-2-brompmercurio-9-oxabicyclo[4.2.1]nonane and of trans-2-bromomercurio-9-oxabicyclo[3.3.1]nonane in methanol with added sodium bromide, in dichloromethane and in pyridine, and from the bromination of 5-trimethylsilyloxycyclo-octene and of 5-t-butyloxycyclo-octene have been determined using 13C n.m.r. spectroscopy. Whereas the product distributions are generally in keeping with established mechanisms, the bromodemercuriation of the [3.3.1]mercurial in methanol with added sodium bromide affords the trans-[4.2.1]bromide as the major product. It is suggested that this novel skeletal rearrangement occurs via a sequence of deoxymercuriation and bromination.

Quantitative estimate of the orientational persistence length of flexible elongated micelles of cetylpyridinium bromide

The experimental results obtained previously (G. Porte, J. Appell, and Y. Poggi, J. Phys. Chem. 84, 3105 (1980); J. Appell and G. Porte, J. Colloid Interface Sci. 81, 85 (1981)) on semiflexible rod-like micelles of cetylpyridinium bromide in aqueous solutions with added sodium bromide are reinterpreted taking into account the distribution in size of the micelles (G. Porte and J. Appell, J. Phys. Chem. 85, 2511 (1981)). This allows a quantitative estimate of the persistence length: 1 = 200 ± 50 A ̊ . The origins of this persistence length are probably twofold: a steric hindrance and short-range interactions between the polar heads.

Oxymetallation. Part 14. Modified procedures for t-butyl peroxymercuriation and bromodemercuriation that lead to an improved, stereoselective, conversion of non-terminal alkenes into β-bromoalkyl peroxides

Stereospecific trans-peroxymercuiation of non-terminal alkenes with little or no accompanying acyloxymercuriation has been accomplished by using mercury(II) acetate under conditions of equilibrium control induced by the presence of 20 mol% of perchloric acid. Bromodemercuriation of the derived peroxymercurials, using bromine in methanol with added sodium bromide, stereoselectively affords β-bromoalkyl peroxides with predominant retention of configuration. Neither of the modified procedures is effective in improving the preparation of peroxides derived from norbornene. Ten diastereoisomerically pure bromoperoxides have been isolated by silica chromatography and characterised by 13C n.m.r. spectroscopy. Configurations have been assigned to the cyclohexene and norbornene derivatives on the basis of their 200 MHz 1H n.m.r. spectra.

Kinetics and mechanism of the denitrosation of nitrosamines in ethanol

Rate constants have been determined for the denitrosation of N-methyl-N-nitrosoaniline (NMNA), N-nitrosodiphenylamine (NDA), and N-methyl-N-nitrosotoluene-p-sulphonamide (MTS) in ethanolic solutions of hydrogen chloride. For both NMNA and NDA the change is reversible in the absence of a trap for the nitrosyl chloride formed; the equilibrium position is dependent upon [HCl]. A kinetic analysis in the case of NMNA gives the rate constants for both the forward and reverse reactions. A more accurate determination of the forward rate constant was obtained for both NMNA and NDA by using an excess of added ascorbic acid to remove the free nitrosating species. Under these conditions the rate law, rate =k2[Nitrosamine][HCl], prevails. The reaction of MTS was irreversible even in the absence of a nitrite trap and the same rate law was established. All three reactants show the absence of catalysis by added sodium bromide and potassium thiocyanate and gave kinetic deuterium solvent isotope effects kEtOH/kEtOD in the range 2.6–3.8. The results are in accord with a rate-determining proton transfer to the nitrosamine, contrasting with the behaviour (of NMNA and NDA) in water solvent. The rate of denitrosation of NMNA decreases as water is added to the solvent, and nucleophilic catalysis begins to be effective. The Fischer–Hepp rearrangement of NDA is observed when ascorbic acid is absent; the rate constant for rearrangement is much less than that for denitrosation at the same acidity.

Micellar catalysis of anilide hydrolysis

The rate of hydrolysis of several anilides is catalysed by cationic micelles (cetyltrimethylammonium bromide), and inhibited by anionic micelles (sodium lauryl sulfate). The magnitude of catalysis is greatest for those anilides which contain the most hydrophobic R groups (R = C7H15 and Ph) and is less for those containing less hydrophobic R groups (R = Me). The magnitude of catalysis is greater for compounds activated by nitro groups than for those activated by a ring nitrogen atom. The catalysis is inhibited by added sodium bromide. There is no evidence that anilide hydrolysis in a micellar environment involves dianionic intermediates. Micellar catalysis of anilide hydrolysis is much greater than for ester hydrolysis.