Micellar rate enhancement studies in mixed sodium fluorocarbon/hydrocarbon surfactant solutions

Abstract

. Can. J. Chem. 70, 1581Chem. 70, (1992. Stopped-flow kinetic studies were conducted in mixed micellar solutions of fluorocarbon and hydrocarbon anionic surfactants to determine the prevalent micellar form. The probe reaction was the ~i,~~/~~ridine-2-azo-~-dimeth~lani-line (PADA) complexation, which is many times accelerated in the presence of anionic micelles. Binding constants for Ni,;+ and PADA partitioning between bulk solution and micelles were determined through the murexide technique and solubility measurements respectively and the molar reaction volume was obtained from the Robinson equation. The three binary surfactant systems investigated had sodium perfluoroheptanoate as the fluorocarbon surfactant while the hydrocarbon surfactants were sodium decylsulfate, sodium nonanesulfonate, and sodium octanesulfonate. The kinetic results were consistent with unimicellar composition in all three systems which was not the behaviour previously found with the sodium octane sulfonate / sodium perfluoroctanoate system. The difference was attributed to closer similarity in the surfactant pair hydrophobicities as revealed through their critical micelle concentrations. Another finding was that mixed micelles synergistically can lead to a much greater solubilization of PADA than is possible through either of the pure surfactants.TERRENCE J. CONNOLLY et VINCENT C. REINSBOROUGH. Can. J. Chem. 70, 158 1 (1992). Dans le but de determiner la forme micellaire prevalante, on a realis6 des Ctudes cinetiques a flux stoppC sur des solutions micellaires d'agents de surface anioniques fluoro-et hydro-carbonCs. La rCaction indicatrice utilisCe est la complexation ~i,~+/~~ridine-2-azo-~-dim~th~laniline (PADA) qui est fortement accC1CrCe en prCsence de micelles anioniques. Les constantes de fixation du Ni$+ et de partition du PADA entre la masse de la solution et les micelles ont Ct C dCterminCes respectivement B l'aide de la technique du murexide et de mesures de solubilitC et on a CvaluC le volume molaire de la reaction grdce B 1'Cquation de Robinson. Les trois systkmes binaires d'agents de surface Ctudies contenaient du perfluoroheptanoate de sodium comme agent de surface fluorocarbonC alors que les agents de surface hydrocarbonCs Ctaient le dCcylsulfate de sodium, nonanesulfonate de sodium et octanesulfonate de sodium. Dans les trois systbmes, les rCsultats cinetiques sont en accord avec la composition unirnicellaire; ce comportement est diffCrent de celui observe antkrieurement avec le systbme octanesulfonate de sodium / perfluorooctanoate de.sodium. On attribue la difference B la plus grande similarit6 dans les hydrophobicites des paires d'agents de surface qui sont rCvClCes par leurs concentrations micellaires critiques. Une autre observation a trait au fait que les micelles mixtes peuvent agir par synergie pour conduire i une solubilisation beaucoup plus grande du PADA que celle possible par chacun des agents de surface agissant seuls.[Traduit par la rCdaction]

Influence of Urea on Sodium Decyl Sulfate Micellization by Kinetic and Solubility Studies

“…Relatively crude assumptions, e.g., that the micelles do not change in size and the value of the CMC corresponds to the free surfactant concentration in micellar solution, do not prevent a successful quantitative correlation of multisourced experimental results in many surfactant systems including microemulsions . The simplified Robinson variant of this kinetic expression takes the form where R is the ratio of the observed pseudo-first-order rate coefficients, with surfactant and without any surfactant present, i.e., s k obs / o k obs ; C is the concentration of the micellized surfactant or ( C T − CMC) where C T is the total surfactant concentration; V is the reaction volume per mole of micellar surfactant. , K PADA and K Ni are the partitioning constants for each of the reactants of the probe reaction distributing between the bulk solution and the micelles. K PADA is defined as ( S s − S o )/ CS o where S is the solubility of PADA and the subscripts correspond to the two different media, micellar surfactant solution and water, respectively.…”

“…The principal investigative procedure adopted in the present work was micellar catalysis using the probe complexation reaction of Ni 2+ with the organic ligand, trans -pyridine-2-azo- p -dimethylaniline or PADA. The kinetic parameters of this reaction as obtained through the Robinson version , of the pseudophase model for micellar catalysis , are sensitive to variations in micelle structure and dynamics. − This technique seemed appropriate because debate revolves around whether urea interacts more significantly with the solvent (“indirect mechanism”) or with the micelles (“direct mechanism”) in bringing about the observed changes in properties in surfactant solution. ,, Catalysis takes place within the micelle so, if urea does not partition into the micelle as postulated by the proponents of the indirect mechanism, then ideally there should be very little modification to the normal kinetic pattern of the probe reaction upon urea addition. PADA solubility measurements were required as ancillary to the kinetic analysis but also they independently provide another insight into micellar phenomena …”

“…The kinetic parameters of this reaction as obtained through the Robinson version 4,5 of the pseudophase model for micellar catalysis 6,7 are sensitive to variations in micelle structure and dynamics. [8][9][10] This technique seemed appropriate because debate revolves around whether urea interacts more significantly with the solvent ("indirect mechanism") or with the micelles ("direct mechanism") in bringing about the observed changes in properties in surfactant solution. 2,3,11 Catalysis takes place within the micelle so, if urea does not partition into the micelle as postulated by the proponents of the indirect mechanism, then ideally there should be very little modification to the normal kinetic pattern of the probe reaction upon urea addition.…”

Metal ion extraction in microheterogeneous systems

“…The kinetics of complexation of Ni 2+ by PADA in anionic mixed micelles of fluorinated-hydrogenated surfactants have shown synergistic PADA solubilisation [89], but a lower solubilisation ability for the pure fluorinated micelles (for a same micellar volume). Pure fluorinated micelles were considered in the study of kinetics of water replacement in the palladium complex of tetraethyldiethylenetriamine by monoalkylthioureas [90].…”

Micellar catalysis in mixed anionic/cationic surfactant systems

“…Anioniclcationic (4) and surfactant mixtures (5)(6)(7)(8). The chosen concentration ranges mirror the complete miscibility ranges in SDS-rich solutions.…”