Soret effect in surfactant systems and microemulsions
Final Report Abstract
In the project we investigated the thermal diffusion behavior of binary water‐surfactant mixtures and microemulsions consisting of H2O/n‐alkane/C12E5 (pentaethylene glycol monododecylether) using the n‐alkanes: n‐octane, n‐decane, n‐dodecane, and n‐tetradecane. The measurements were performed using the so‐called infra‐red thermal diffusion forced Rayleigh scattering (IR‐TDFRS) method which avoids the addition of a dye, which turned out to be surface active. By varying the chain length of the n‐alkanes we are able to study the thermodiffusion behavior of droplets of different sizes under isothermal conditions, i.e. at the same temperature. In contrast to hard colloids the soft microemulsions have the advantage that they allow to adjust the size without changing the chemistry of the system such as the grafting density of the surface groups. All performed studies confirmed the linear radial dependence of the Soret coefficient. With this systematic microemulsion study it was for the first time possible to investigate thoroughly the proposed relationship between the Soret coefficient and the temperature derivative of the product of the oil/water interfacial tension σab and the length of the so‐called transition layer l. Analyzing all results for the microemulsions containing different alkanes simultaneously it was possible to determine the transition layer l. It turned out that the proposed relation is compatible with the thermodiffusion data of the nonionic microemulsions. Although the physical origin of transition layer l is not very well‐defined, we found rather small values of 0.1 and 0.2 nm, which correspond to typical van der Waals radii and are considerably smaller than the width of the diffuse amphiphilic film determined by SANS. The results obtained in the project will be valuable for several practical applications. The dominant application is the Microscale Thermophoresis which utilizes the Soret effect for monitoring biochemical interactions. According to our results their working equation assuming a quadratic radial dependence of the Soret coefficient needs to be revised. Additionally the better understanding of the interfacial contribution will also be useful for the analysis of protein‐vesicle interactions. The outcome of the project will be valuable for future development of microemulsions as nano‐containers used in technical applications (e.g., catalysis, gas storage, low‐weight building materials, drug delivery). In many industrial and medical applications temperature gradients occur and a better understanding of the thermal diffusion process will be helpful to optimize those processes.
Publications
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Thermal diffusion forced Rayleigh scattering setup optimized for aqueous mixtures, J. Phys. Chem. B, 111, 14169-14174 (2007)
Wiegand, S., H. Ning, and H. Kriegs
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Soret effect of nonionic surfactants in water studied by different transient grating setups, J. Phys. Chem. B, 112, 10927-10934 (2008)
Ning, H., S. Datta, T. Sottmann, and S. Wiegand
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Soret Effect of n-Octyl beta-D-Glucopyranoside (C(8)G(1)) in Water around the Critical Micelle Concentration, J. Phys. Chem. B 114, 2118-2123 (2010)
Arlt, B., S. Datta, T. Sottmann, and S. Wiegand
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Thermal Diffusion of Oligosaccharide Solutions: The Role of Chain Length and Structure, J. Phys. Chem. B 114, 10740-10747 (2010)
Blanco, P., H. Kriegs, B. Arlt, and S. Wiegand
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Non-ionic Binary Surfactant Systems and Microemulsions as Model Systems for Thermal Diffusion Studies, hD-Thesis Universität zu Köln, Cuvillier Verlag, Göttingen (2011)
S. Datta
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Development of a Thermogravitational Microcolumn with an Interferometric Contactless Detection System, J. Phys. Chem. B 116, 13889-13897 (2012)
Naumann, P., A. Martin, H. Kriegs, M. Larrañaga, M.M. Bou-Ali, and S. Wiegand
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Thermal Diffusion in binary Surfactant Systems and Microemulsions, PhD-Thesis Universität zu Köln, Grafische Medien, Forschungszentrum Jülich, (2012)
B. Arlt
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Thermogravitational microcolumn for determining the thermal diffusion coefficient of biological fluids and synthetic and biological colloidal fluids, EP12382015. 2012
Martin, A., M.M. Bou-Ali, E. Gandarias, P. Aristimuño, and S. Wiegand
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Soret Coefficient in Nonionic Microemulsions: Concentration and Structure Dependence, J. Phys. Chem. B, 117, 5614-5622 (2013)
Naumann, P., N. Becker, S. Datta, T. Sottmann, and S. Wiegand
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Investigation of the thermodiffusion behaviour of complex fluids and development of new methods, PhD-Thesis Universität Düsseldorf (2014)
P. Naumann
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Isothermal Behavior of the Soret Effect in Nonionic Microemulsions: Size Variation by Using Different n-Alkanes, The Journal of Physical Chemistry B, 118, 3451-3460 (2014)
Naumann, P., S. Datta, T. Sottmann, B. Arlt, H. Frielinghaus, and S. Wiegand
