Volumes and heat capacities of transfer of ammonium salts from water to aqueous octyldimethylamine oxide at 25 °C

Abstract

. 66, 767 (1988).The effect of an additive on a water-surfactant system can be studied through thermodynamic functions of transfer of the additive from water to aqueous solutions of the surfactant. These thermodynamic functions often go through extrema in the region of the critical micellar concentration (cmc) of the surfactant. As it can be shown with a simple chemical equilibrium model, the general shape of the transfer functions is primarily related to the pair-wise hydrophobic interactions between the additive and the surfactant monomers, to a shift in the monomer-micelle equilibrium and to the distribution of the additive between the aqueous phase and the micelles. Medium and electrostatic effects are also possible, especially with ionic systems. To separate these effects and identify the salts which distribute themselves in the micelles, the volumes and heat capacities of transfer of hydrophobic ammonium salts from water to aqueous solutions of dimethyloctylamine oxide have been investigated. The short chain salts have only a small effect on monomer-micelle equilibrium by salting out the monomers, whereas the more hydrophobic ones participate also to the micellization process, shifting more strongly the surfactant monomer-micelle equilibrium.DANIEL HCTU et JACQUES E. DESNOYERS. Can. J. Chem. 66, 767 (1988).L'effet d'un additif sur un systkme eau-tensioactif peut Ctre CtudiC par le biais des fonctions de transfert de l'additif de l'eau aux solutions aqueuses du tensioactif. Ces fonctions thermodynamiques passent souvent par un extremum dans la region de la concentration micellaire critique (cmc) du tensioactif. Comme il peut Ctre dCmontrC B l'aide d'un modkle simple d'tquilibre chimique, l'allure gCnCrale des fonctions de transfert est principalement relike aux interactions hydrophobes par paires entre les monomkres de l'additif et du tensioactif, au dCplacement de 1'Cquilibre monomkres-micelles du tensioactif, ainsi qu'i la distribution de l'additif entre la phase aqueuse et les micelles. Des effets de milieu ainsi qulClectrostatiques peuvent aussi jouer un r61e important, particulikrement dans le cas de systkmes ioniques. Afin de sCparer ces effets et d'identifier les sels qui participent B la micellisation, les volumes et capacitCs calorifiques dc transfert de sels hydrophobes d'ammonium de I'eau aux solutions aqueuses d'oxyde dloctyldimCthylamine ont CtC investiguks. Les sels a courtes chaines ont seulement un petit effet sur 1'Cquilibre monomkres-micelles du tensioactif, dh a un effet de relargage, alors que les sels B plus longues chaines participent en plus i la micellisation, dCpla~ant davantage 1'Cquilibre du tensioactif.

Volumetric Mixing in Anionic/Nonionic, Cationic/Nonionic, and Anionic/Cationic Mixed Micelles

“…Paar reports an accuracy namics (i.e., the free energy of mixing) only at the onset of of {1.5 1 10 06 g/cm 3 in the measured densities (6); how-mixed micelle formation and that Eqs. [2] and [3] are not ever, the actual error was approximately {1.5 1 10 05 g/cm 3 necessarily valid at total surfactant concentrations greater (5), due to the fluctuations of the water bath temperature. than the CMC m .…”

“…The volumetric properties of surfactants in aqueous solution have been widely studied, to investigate surfactant/sol-EXPERIMENTAL vent interactions and the thermodynamics of micelle formation. Very few studies, however, have investigated the voluMaterials metric properties of surfactants in mixed surfactant systems (1)(2)(3)(4), even though such studies may yield valuable inforSodium dodecyl sulfate (SDS) was the anionic surfactant mation about the thermodynamics of mixed micelle forma-used in this study. The SDS was purchased from Baxter tion.…”

“…The regular solution theory pseudowater (ion-exchanged twice and then treated with activated phase separation model for mixed micelle formation, Eqs. carbon), ACS-grade sodium chloride (Mallinckrodt), 0.01 [2] - [5], predicts the lowest total surfactant concentration N hydrochloric acid and 0.01 N sodium hydroxide solutions at which the first mixed surfactant micelle forms in the bulk (Fisher Scientific), and disposable 3-ml plastic hypodermic solution (CMC m ), as a function of the mixed surfactant syringes (Becton Dickinson).…”

“…The density meter was calibrated at 30.00ЊC using solution theory pseudo-phase separation model for mixed air and DI water (6), and then the solvent and surfactant micelle formation (Eqs. [2] - [5]) describes the thermodysolution densities were measured. Paar reports an accuracy namics (i.e., the free energy of mixing) only at the onset of of {1.5 1 10 06 g/cm 3 in the measured densities (6); how-mixed micelle formation and that Eqs.…”

“…Once the interaction parameter for mixed micelle formation (W mic /RT ) was deter-surfactant concentrations equal to, or infinitesimally greater than, the onset of mixed micelle formation (C T à CMC m ) mined, CMC m values at any mixed surfactant composition (Y 1 Å Q 1 and Y 2 Å Q 2 , at the onset of mixed micelle forma-and that it is valid at total surfactant concentrations greater than the onset of mixed micelle formation (C T ú CMC m ) tion) could be predicted using Eqs. [2] - [5].…”