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| Home > Publications database > Thermal diffusion in binary surfactant systems and microemulsions |
| Dissertation / PhD Thesis/Book | PreJuSER-17829 |
2012
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-819-8
Please use a persistent id in citations: http://hdl.handle.net/2128/4697
Abstract: In this work the thermal diffusion behavior of micellar systems and microemulsions is studied. These model systems are used to investigate two open questions. The first question focuses on the influence of the micelle formation around the critical micelle concentration ($\textit{cmc}$) on the thermal diffusion behavior. In order to answer this, we studied the thermal diffusion behavior of the nonionic surfactant n–Octyl β–D–glucopyranoside (C$_{8}$G$_{1}$) in water, which shows a fairly high $\textit{cmc}$ at 0.65 wt% for different concentrations between w = 0.25 wt% and w = 2.0 wt% in a temperature range from T = 15 $^{\circ}$C to 60 $^{\circ}$C using the classical and infrared thermal diffusion forced Rayleigh scattering ($\textit{TDFRS}$) setup. The $\textit{cmc}$ is independently determined by surface tension measurements. In classical TD-FRS experiments, 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 $\textit{cmc}$. This result agrees with a recent thermal lens study [Santos et al., Phys.Rev. E 2008, 77, 011403 ], which showed, also in the presence of dye, a pronounced change of the matter part of the thermal lens signal around the $\textit{cmc}$. We found that the change in the thermal diffusion properties 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 inversion of S$_{T}$ as has also been found for solutions of hard spheres at higher concentrations. We also studied the sugar surfactants n–Heptyl β–D–glucopyranoside (C$_{7}$G$_{1}$) and n–Octyl β–D–maltopyranoside (C$_{8}$G$_{2}$), to investigate the influence of the number of head groups and the length of the alkyl chain on the thermal diffusion behavior. In the low concentration regime around the $\textit{cmc}$, the abrupt change of S$_{T}$ was confirmed for C$_{7}$G$_{1}$ and C$_{8}$G$_{2}$. Further, the sign change in the high concentration regime was confirmed. The second question is the radial dependence of the Soret coefficient. It is controversially discussed whether the radial dependence of S$_{T}$ is quadratic [...]
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