Diffusion in Surfactant Systems Studied by Forced Rayleigh Scattering

Abstract

The technique of forced Rayleigh scattering (FRS) was used to obtain information on the microstructure of two surfactant systems: i.e. bis(2-ethylhexyl) sulfosuccinate (AOT)/octanol/water and tetradecyldimethylammonium oxide (TDMAO)/tetradecyltrimethylammonium bromide (TTMAB)/hexanol/water. Diffusion coefficients of the dye molecules congo red and methyl red, and of surfactant aggregates labeled with these dye probes, have been determined. In the L2 (microemulsion) phase of AOT/octanol/water stained with congo red, diffusion coefficients have been found to decrease with increasing water content. In contrast, at the transition from the L2 to the cubic phase, a continuous increase was observed. Although submicroscopically bicontinuous structures may exist in the microemulsion, the interconnectivity of the rodlike aggregates is not sufficient to enable free diffusion of the water soluble dye over the distance range investigated by FRS. Thus the determined diffusion coefficients reflect the motion of dynamic structural units. The situation is different in the cubic phase: here the long range order makes it possible for the dye molecules to diffuse in the water channels. Compared to unhindered motion in aqueous solution, the diffusion coefficient is reduced to about 20% by steric obstruction effects. The continuous increase of the diffusion coefficient at the phase transition reflects the close structural relationship between the two phases near the phase boundary, whilst there is a remarkable difference in the L2 phase further away. For the system TDMAO/TTMAB/hexanol/water the transition from the micellar L1 to the vesicular Lα phase with increasing alcohol content has been investigated. The lipophilic dye methyl red is anchored in the surfactant layers, as is verified by polarization microscopy. In the L1 phase there is a transition from spherical to rodlike micelles. Self-diffusion coefficients of these spheres and rods have been measured, and the results have been compared to theoretical values, calculated by the model of Edwards and Doi for concentrated solutions of rodlike molecules. In the Lα phase the vesicles are densely packed, so that the diffusion coefficients originate from the motion of the dye probe within the surfactant bilayers and from an exchange between different bilayers. In complementary experiments, the mobility of the vesicles in an electric field has been probed.

The spectral study of azo dye and cationic surfactant interaction in ethanol-water mixture

“…[6][7][8][9][10][11] There are no specified studies of azo dye methyl red with cationic surfactant dodecyl trimethyl ammonium bromide using various methods. [12][13][14][15][16][17] For detailed analysis, we reviewed in literature 13 that the effect of cationic surfactants on the dissociation constant of methyl red by spectrophotometric technique. The absorbance peak of methyl red was decreased drawn after 10 and 20 min of treatment in water due to photodegradation through kinetic analysis and complete photodegradation of the 35 min treatment, which is based on azo dye photosensitization.…”

UV-VIS studies on interaction between sodium dioctylsulfosuccinate (AOT) and methyl red

“…There have been some spectrophotometric measurements of dyes in the presence of surfactants 12,[20][21][22][23][24][25][26][27] and particularly, even some studies of methyl red with AOT were noticed in the literature. [28][29][30][31] Our aim was to see the spectrophotometric measurements of methyl red in AOT/methanol and AOT/methanol/water systems. However, there is no literature on the UV-Vis study of methyl red in AOT/methanol and with increasing amounts of water in methanol.…”

Tracer diffusion properties of core–shell latex films studied by photoinduced grating relaxation

“…polymer phase, water phase, interface) and can, thus, provide complementary information, e.g., on water loss and surfactant mobility or polymer diffusion. The photoinduced grating relaxation technique, better known as Forced Rayleigh Scattering (FRS) in polymer science (the notation used throughout this paper), which relies on probing the dynamics of a tracer molecule, has shown to be a powerful tool to investigate the local mobility distributions and microstructure in phase separated systems such as block copolymers,10 drying latex films, etc.,7 yielding information on diffusion and spatial inhomogeneities in polymer systems10–18 and drying latex dispersions 7–9. The transport properties in heterogeneous systems are particularly interesting, since the supramolecular structure imposes spatial constraints on a diffusing moiety, which in special cases can lead to anisotropic behavior 19, 20.…”