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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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Article information


Submitted
19 Dec 2014
Accepted
02 Feb 2015
First published
11 Feb 2015

This article is Open Access

Soft Matter, 2015,11, 2379-2386
Article type
Paper
Author version available

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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