Abstract
Methods to move solvated molecules are rare. Apart from electric fields, only thermal gradients are effective enough to move molecules inside a fluid. This effect is termed thermophoresis, and the underlying mechanisms are still poorly understood. Nevertheless, it is successfully used to quantify biomolecule binding in complex liquids. Here we show experiments that reveal that thermophoresis in water is dominated by two electric fields, both established by the salt ions of the solution. A local field around the molecule drives molecules along an energy gradient, whereas a global field moves the molecules by a combined thermoelectrophoresis mechanism known as the Seebeck effect. Both mechanisms combined predict the thermophoresis of DNA and RNA polymers for a wide range of experimental parameters. For example, we correctly predict a complex, nonlinear size transition, a salt-species-dependent offset, a maximum of thermophoresis over temperature, and the dependence of thermophoresis on the molecule concentration.
- Received 6 February 2014
DOI:https://doi.org/10.1103/PhysRevLett.112.198101
© 2014 American Physical Society
Synopsis
Why Heat Moves Molecules in Solution
Published 13 May 2014
Researchers have developed a complete theory for thermophoresis—the process by which molecules in a liquid move under the influence of temperature—and tested it under a wide range of conditions.
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