Soret Effect of n-Octyl β-d-Glucopyranoside (C₈G₁) in Water around the Critical Micelle Concentration

Abstract

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.

Soret Coefficient in Nonionic Microemulsions: Concentration and Structure Dependence

“…The Soret coefficient decays by only 10% in the investigated concentration range; thus, we can conclude that the increasing volume fraction along path w B will not influence the radial dependence of S T . For higher volume fractions (above 10%), we expect a much steeper decay of S T , as it has been observed for micellar systems, 16 colloidal suspensions, 35 and polymer solutions. 49 Figure 9 summarizes the radial dependence of S T measured along path T , path w B , and path ϕ .…”

Experimental approaches to study thermodiffusion – A review

“…While a dye is used for the light absorption and creation of the temperature grating, it can have negative implications on the thermodiffusion studies. In a recent study by Arlt et al [108], the authors noted a significant impact of the dye on the thermodiffusion process in the non-ionic surfactant n-Octyl b-D-Glucopyranoside (C 8 G 1 )/water system. This observation agreed with the studies of Santos et al [109].…”

Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions

“…However, when the 1,2‐addition was performed in toluene no formation of N‐ tosylamide 3 was observed, and thus even less than in dioxane (9 %) (entries 1 and 2). Subsequently, the catalysis was performed in a mixture of water and toluene with the addition of low amounts of C 8 G 1 surfactant, i. e. at γ=2 wt%, which is clearly above the CMC (note that in pure H 2 O the CMC of C 8 G 1 amounts to 0.6 wt% at T =40 °C) [33] . At this composition the coexistence of a microemulsion with an excess water and oil phase is expected.…”