Diffusion in associating nonelectrolyte mixtures: stepwise aggregation and micelle formation

Abstract

Equations have been developed to predict diffusion coefficients and Onsager coefficients for associating nonelectrolyte solutes in binary or multicomponent solutions with any number of association equilibria. The equations are used to interpret previously reported data for binary diffusion with stepwise association of ethanol and N-methylacetamide in carbon tetrachloride solutions. Diffusion of Triton X-100, a non-ionic micelle-forming surfactant, is also analyzed. In contrast to the gradual decrease in the diffusivity caused by stepwise association, formation of micellar aggregates produces a sharp drop in the diffusivity at the critical micelle concentration. The relation between interdiffusion coefficients and intradiffusion coefficients for associating nonelectrolyte solutes is discussed. DEREK G. LEAIST. Can. J. Chem. 66, 1129 (1988). On a dtveloppt des tquations qui permettent de prtdire les coefficients de diffusion et les coefficients dlOnsager de solutts non-tlectrolytes qui s'associent dans des solutions binaires ou B plusieurs composants et qui comportent n'importe quel nombre d'kquilibres d'association. On a utilist les tquations pour interprtter des donnkes rapporttes anttrieurement pour de la diffusion binaire impliquant une association par ttapes de l'tthanol et du N-mtthylacttamide dans des solutions de tttrachlorure de carbone. On a aussi analyst la diffusion du Triton X-100, un agent de surface non-ionique qui forme des micelles. Par opposition avec la diminution graduelle de la possibilitt de diffusion provoqute par cette association par ttapes, la formation d'aggrkgats micellaires provoque une diminution importante de la possibilitk de diffusion B la concentration micellaire critique. On discute de la relation entre les coefficients d'interdiffusion et les coefficients d'intradiffusion pour les solutks non-tlectrolytes qui s'associent.[Traduit par la revue] Introduction Many nonelectrolyte solutes associate (1). Aqueous urea, for example, is extensively dimerized (2,3). In nonpolar solvents, carboxylic acids and phenols form dimers (4-7). Other solutes, such as nucleic acids (8), amides (9-1 l), and certain dyes (12), associate in a stepwise manner to form chain-like aggregates. Non-ionic surfactants illustrate an extreme case of association in which micellar clusters containing several hundred molecules can form (13-16).The work reported here was undertaken to study the diffusion behavior of associating nonelectrolytes. The effects of association on diffusion are interpreted by determining changes in the solute mobility and the free energy gradient, the driving force for diffusion.Binary diffusion of dimerizing solutes (2,(17)(18)(19)(20) and ternary diffusion of solutes A and B that form complex AB (21) have already been studied. The equations developed in the present paper extend the earlier treatments to nonelectrolyte mixtures that contain arbitrary numbers of components and association equilibria.Weinheimer et al. (15) have reported an approximate expression for estimating the diffusion...

Coupled diffusion of butanol solubilized in aqueous sodium dodecylsulfate micelles

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Theoretical Comparisons of the Concentration-Dependent Diffusion Coefficients from Dynamic Light Scattering and Taylor Dispersion Analysis

“…In the next two sections, a prior theoretical derivation [9,14,15] of the intrinsic mutual diffusion coefficient for self-association is presented. In general, a self-associating solute diffuses as its polymers i.e., monomers (A 1 ), dimers (A 2 ), trimers (A 3 ) etc.…”

“…In general, a self-associating solute diffuses as polymers i.e., monomers, dimers, trimers etc. Using a simplified model for association, expressions for the intrinsic (or unweighted) mutual diffusion coefficients of associating solutes have been derived as a function of concentration [9,14,15]. However, for measurements, due to characteristics inherent in the type of analysis, weighted average diffusion coefficients are obtained …”

Formation of a Novel Type of Reverse Microemulsion System and Its Application in Synthesis of the Nanostructured La0.95Ba0.05MnAl11O19 Catalyst.

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“…It has been reported that ethanol molecules exist as selfassociated aggregates through hydrogen bonds between ethanol molecules in nonpolar solvents. 6,7 Besides, Mizuno et al 8,9 investigated the self-association behavior of ethanol molecules in an aqueous solution by NMR and FT-IR. Their results showed that self-association of ethanol molecules in an aqueous solution occurs over the whole range of ethanol concentration, and the hydrogen bonds become stronger with increase of the size of the ethanol aggregates, due to a cooperative effect of hydrogen bonding.…”