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Issue 12, 2015
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Direct measurement of thermophoretic forces

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Abstract

We study the thermophoretic motion of a micron sized single colloidal particle in front of a flat wall by evanescent light scattering. To quantify thermophoretic effects we analyse the nonequilibrium steady state (NESS) of the particle in a constant temperature gradient perpendicular to the confining walls. We propose to determine thermophoretic forces from a “generalized potential” associated with the probability distribution of the particle position in the NESS. Experimentally we demonstrate, how this spatial probability distribution is measured and how thermophoretic forces can be extracted with 10 fN resolution. By varying temperature gradient and ambient temperature, the temperature dependence of Soret coefficient ST(T) is determined for r = 2.5 μm polystyrene and r = 1.35 μm melamine particles. The functional form of ST(T) is in good agreement with findings for smaller colloids. In addition, we measure and discuss hydrodynamic effects in the confined geometry. The theoretical and experimental technique proposed here extends thermophoresis measurements to so far inaccessible particle sizes and particle solvent combinations.

Graphical abstract: Direct measurement of thermophoretic forces

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Publication details

The article was received on 19 Dec 2014, accepted on 02 Feb 2015 and first published on 11 Feb 2015


Article type: Paper
DOI: 10.1039/C4SM02833C
Citation: Soft Matter, 2015,11, 2379-2386
  • Open access: Creative Commons BY-NC license
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    Direct measurement of thermophoretic forces

    L. Helden, R. Eichhorn and C. Bechinger, Soft Matter, 2015, 11, 2379
    DOI: 10.1039/C4SM02833C

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