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| Conference Presentation (Plenary/Keynote) | FZJ-2015-06267 |
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2015
Abstract: Thermophoresis or Thermal diffusion, which is also known as the Ludwig–Soret effect, is the phenomenon where mass transport is induced by a temperature gradient in a multi-component system. So far there is only a limited microscopic understanding for fluids. In the recent years the « heat of transfer » concept has been successfully applied to non-polar systems, but in aqueous systems the situations is more complicated due to charge effects and strong specific cross interactions so that this concept fails. It turns out that this simple non-equilibrium environment created by a temperature gradient can be successfully employed to monitor for example the reaction kinetics of large proteins with small substrate molecules, which play an important role in living organisms and drug development. The strong sensitivity of the proteins and other water soluble biomolecules is probably caused by a change in the hydration layer, which is influenced by subtle conformation changes induced by the binding of the substrate molecule. To get a better understanding of these phenomena we investigated systematically various small molecules, microemulsions and colloids by a holographic grating method called infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS). Looking at the various systems we can identify certain rules of thumb which will be discussed. Open questions such as the molecular size dependence of the thermal diffusion coefficient and its relation with the interfacial tension and charge effects are considered.Finally we discuss how thermophoresis might be used in the near future as an alternative strategy to design synthetic microswimmers, micromotors, or micropumps, which have become promising tools in the field of microfluidics. We give an outlook how locally controlled temperature gradients at very small scales, allow the fabrication of lab-on-chip devices, which can be used to manipulate synthetic and biological colloids. Keywords: Thermophoresis, colloids, aqueous mixtures, holographic grating technique, microfluidic
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