We investigated the chain length dependence of the thermodiffusion behavior of oligosaccharides by the infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS)

The ternary system composed of the ionic liquid surfactant (IL-S) 1-butyl-3-methylimidazolium dodecylsulfate ([Bmim][DodSO4]), the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]), and toluene has been investigated. Three major mechanisms guiding the structure of the isotropic phase were identified by means of conductometric experiments, which have been correlated to the presence of oil-in-IL, bicontinuous, and IL-in-oil microemulsions. IL-S forms micelles in toluene, which swell by adding RTIL as to be shown by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) experiments. Therefore, it is possible to form water-free IL-in-oil reverse microemulsions ≤10 nm in size as a new type of nanoreactor.

In this work we investigate the thermodiffusion behavior of microemulsion droplets of the type H2O/n-alkane/C12E5 (pentaethylene glycol monododecyl ether) using the n-alkanes: n-octane, n-decane, n-dodecane, and n-tetradecane. In order to determine the thermodiffusion behavior of these microemulsion droplets, we apply the infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS) technique. We measure the Soret coefficient (ST) as function of the structure upon approaching the emulsification failure boundary (efb) and as a function of the radius of the spherical o/w microemulsion droplets close to the efb. By varying the chain length of the n-alkanes, we are able to study the thermodiffusion behavior of spherical o/w microemulsion droplets of different sizes at the same temperature. In the investigated range a linear dependence of the Soret coefficient as function of the radius was found. By use of a proposed relationship between the Soret coefficient and the temperature dependence of the interfacial tension, the transition layer l could be determined for the first time. Additionally, small angle neutron scattering (SANS) experiments are performed to determine the size and to prove that the shape of the microemulsion droplets is spherical close to the efb. Accordingly, the scattering curves could be quantitatively described by a combination of a spherical core-shell form factor and sticky hard sphere structure factor.

We studied the thermal diffusion behavior of the nonionic surfactant C(8)G(1) (n-octyl beta-D-glucopyranoside) in water for different concentrations between w = 0.25 wt% and w = 2.0 wt% in a temperature range from T = 15 to 60 degrees C using the classical and infrared thermal diffusion forced Rayleigh scattering (TDFRS) setup. The purpose of the present paper is the investigation of the thermal diffusion behavior of surfactant systems around the critical micelle concentration (cmc), which is independently determined by surface tension measurements. In the classical TDFRS, the surfactant solutions show in the presence of a light-absorbing dye a pronounced change of the thermal diffusion coefficient (D(T)) and the Soret coefficient (S(T)) at the cmc. This result agrees with a recent thermal lens study [Santos et al., Phys. Rev. E 2008, 77, 011403], which also showed in the presence of dye a pronounced change of the thermal lens matter signal around the cmc. We found that this change becomes less pronounced, if the dye is absent or a light source is used, which is not absorbed by the dye. At higher concentrations, we observed a temperature-dependent sign change of S(T) as has also been found for solutions of hard spheres at higher concentrations.