Structure and dynamics in three-component microemulsions

Abstract

NMR self-diffusion coefficients are reported for three-component micromulsions formed from didodecyldimethylammonium bromide/water/alkane. For hexane through tetradecane the oil diffusion coefficients are approximately half as large as those of the bulk oils and independent of composition. Therefore, the systems are oil continuous through the entire one-phase region. The diffusion coefficients for the surfactant are small and independent of composition. The water self-diffusion coefficients decrease with added water for hexane through dodecane and change in a manner consistent with the abrupt conducting-nonconducting transition known to occur in this system. The microemulsions are bicontinuous in the conducting regions and disconnected water-in-oil droplets in the nonconducting regions of the phase diagrams. The phenomena reported clearly demonstrate the interplay between forces due to oil penetration and those due to head-group interactions which control curvature and therefore microemulsion structure.

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited

“…The axes represent the weight percent for each component. The green line passing toward the oil corner is drawn from the oil corner through the end points of the conducting regions [79]. The pink region to the left of the single-phase region marks the gradual transition to a viscous gel-like system.…”

Shear thinning in ternary bicontinuous and water‐in‐oil microemulsions

“…DDAB microemulsions have been extensively studied, and the droplet radius in the W/O region is known from small-angle scattering (Barnes et al, 1988a). Self-diffusion coefficients of the oil, water, and surfactant components of the microemulsions have also been measured, and in the w/o region we take this to be equal to the droplet diffusion coefficients (Blum et al, 1985). At compositions where diffusion constants have not been measured, we have used the approximate relationship between viscosity and diffusion coefficient of a dispersion of spheres at volume fractions 1 and 2:v,/q2=D2/D1 (van Blaaderen et al, 1992;Cohen and de Schepper, 1992).…”

“…This form is obtained by using a Stokes' law representation of the sphere diffusion coefficient, and corresponds to infinite dilution of droplets. In might also be regarded as the diffusion of a droplet within a coordination cage of neighboring spheres: the short time limit of the diffusion coefficient, as distinct from the long time value obtained from PGFT-NMR (Blum et al, 1985). Experiments on hard sphere systems and theoretical analysis have both shown a dependence of the short time diffusion coefficient on volume fraction of dispersed phase, so this definition of the Peclet number is not strictly appropriate for concentrated dispersions.…”

“…DDAB forms microemulsions with a variety of hydrocarbons over a wide range of compositions (Chen et al 1984;Blum et al, 1985;Barnes et al, 1988a, b), exhibiting both Correspondence concerning this article should be addressed to G . G. Warr.…”

“…The one phase microemulsion region for DDAB + oil + water is shown on a ternary phase diagram in Figure 1. The structure of these microemulsions has been well studied by numerous techniques (Chen et al, 1984;Blum et al, 1985;Barnes et al, 1988a,b). The generally accepted picture is of interconnected water tubes coated with an oriented monolayer of surfactant and dispersed in an oil continuum.…”