Berlin 2015 – scientific programme

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BP: Fachverband Biologische Physik

BP 53: Complex Fluids and Soft Matter (joint BP/DY/CPP)

BP 53.7: Talk

Friday, March 20, 2015, 11:15–11:30, H 1058

Bridging from ionic to non-ionic thermophoresis — •Manuel Wolff, Michael Nash, and Dieter Braun — Center for Nanoscience, LMU, Munich, Germany

Thermal gradients drive molecules in solutions, an effect termed thermophoresis. Interest in aqueous thermophoresis was recently triggered by its widespread application in biomolecule affinity analysis using infrared-illuminated capillaries.

Theoretical models are debated, not least due to the fact that molecules in water seem to behave significantly different in non-aqueous fluids. By designing fluorescently labeled polymers that are either completely uncharged or whose charge can be tuned by a change in pH, we find that the temperature dependence of ionic and non-ionic polymers is very distinct. Building upon previous models, we find that increasing thermophoresis for rising temperature, often fitted by a heuristic formula proposed by Piazza and attributed to hydrophobic effects, can be fully explained by the Seebeck effect: the temperature dependence of ionic thermophoresis is dominated by the temperature dependent thermophoresis of the small ions in solution. While this dependence is not yet fully known for H⁺ and OH⁻, the thermophoresis of peptide nucleic acid (PNA) with its pH dependent charge is described well across a wide range of pH with reasonable assumptions. These findings offer a new bridge from aqueous thermophoresis to non-aqueous solutions.