Micellar Properties from Hydrodynamic Data

Abstract

Intrinsic viscosities, sedimentation coefficients, and diffusion constants have been used to determine the size, shape, and hydration of nonionic (dimethyldodecylamine oxide) and anionic (sodium dodecyl sulfate) surfactant micelles. From these data it is concluded that the micelles are small, spherical, and highly hydrated (contain -40'% water by volume) in dilute solution. A model for the micelle is postulated and shown to be in agreement with the experimental data.Few measurements have been made of the hydrodynamic properties of micelles where the results have been used to deduce size, shape, or hydration. Kushner, et uL11-3 measured viscosity as a function of concentration for a number of detergents but concluded that hydration of the micelle was an important factor only for a commercial nonyl phenol-ethylene oxide condensate which gave a high intrinsic viscosity. Tyuzgo4 used diffusion coefficients and Stokes' law to calculate hydration for several salts of fatty acids. Other workers5 also used diffusion coefficients to calculate hydration of a series of methoxy polyoxyethylene decanoates and dodecanoates assuming the particles were spherical. Vetter6 used several pieces of hydrodynamic data to deduce that micelles of Aerosol MA contained water, while Hakala7 ignored hydration to conclude from hydrodynamic data that micelles of sodium dodecyl sulfate were ellipsoidal. On the other hand, Stigter, Mysels, and Williams* compared diffusion data with light scattering molecular weights to conclude that sodium dodecyl sulfate micelles were hydrated if a spherical shape vias assumed.I n order to clarify some of these apparently conflicting results, a numbel of hydrodynamic measurements were made on micellar solutions of very pure nonionic and ionic surfactants and the size, shape, and hydration of the micelles were determined from these data. ExperimentalViscosity. The viscosities of the solutions were measured at 30.00 f 0.02" using an Ostwald-Fenske viscometer with a flow time for water of about 220 sec.Flow times were measured to 0.01 sec. with a stop watch. The average deviation for five to seven measurements of a single solution did not exceed =t0.07 sec. The viscometer was calibrated with distilled water and 10% glycerine and the usual equation, = Apt + Bp/t, was used to calculate the viscometer constants. The absolute viscosity and density of water at 30" were taken to be 0.007976 poiseg and 0.99568 g./ml.,Io respectively. The viscosity and density of the glycerine solution were taken to be 0.01024 poise and 1.01927 g./ml., respective1y.l' The surface tension correction, arising from the difference in shape of the nieniscus in the upper and lower bulbs of the viscometer, mas ignored. This is possible because the quantity of interest is the viscosity of the solution relative to the viscosity at the critical micelle concentration, and the surface tension of these solutions was constant above the

An investigation of the solubilization mechanism of sodium octanoate micelles by small-angle X-ray scattering

“…9 = potassium hexanoate, • = sodium octanoate, L5 = sodium decanoate structure with considerable contact between the first carbon atoms of the chain and water. This view of the micellar structure has recently gained rapidly growing support based on a large number of experimental methods [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. It is by no means surprising since the surface occupied by one monomer in the micelle is very large [37].…”

“…Fortunately, due to circumstances shown by Hayter et W441 al., the model used in the interpretation of SAXS-data is still expected to give approximately correct gross geometrical results at concentrations nor far beyond the cmc (in "cmc-units"). Despite the circumspection required in the interpretation of SAXS-data in general, the overall view of micellar structure emerging from SAXS- [7], light- [14], and neutron- [53,54] scattering experiments as well as other instrumental approaches [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] are basically the same. This may expected to be true, especially in cases where changes in a parameter are studied.…”

Etude par viscosité et autodiffusion de solutions aqueuses de divers n-alkyl-benzènesulfonates

“…Ainsi le volume molaire des micelles form6es par Cs ¢ SOa Li a dt6 trouv6 supdrieur ~ celui des micelles formdes par Cs 4 SOa Na, et se pose tout naturellement la question de la valeur de Fhydratation des micelles et des 4tudes sont pr6vues au laboratoire sur la mesure directe de cette hydratation par la ddtermination des coefficients d'autodiffusion de l'eau dans les solutions (Cs ¢ SOa Li q-LiC1) et (Cs ¢ SOa Na q-NaC1) o6 la concentration en sel alcalin est fix6e car la m&hode d'aut0-diffusion est une m&hode hydrodynamique et les erreurs dans le calcul de l'hydratation sont importantes si on ne supprime pas l'effet electrovisqueux (23).…”

Behavior of Surfactant Mixtures at Solid/Liquid and Oil/Liquid Interfaces in Chemical Flooding Systems

“…These three surfactants used here exhibit an increasing trend, suggesting formation of larger aggregates [34,35]. Sedimentation coefficients of n-dodecyl-β-D-maltoside increase from twice cmc and reach a plateau above 5 times cmc, showing a behavior different from that of sodium dodecyl sulfate [36]. For ionic surfactants, the Gibbs free energy of electrostatic interaction between charged molecules predominate the packing interaction in the formation of micelles [37].…”