Direct measurement of thermophoretic forces

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 $S_T(T)$ is determined for $r=2.5\mu m$ polystyrene and $r=1.35\mu m$ melamine particles. The functional form of $S_T(T)$ 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.

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• Thermophoresis of charged colloidal particles
• Noise-induced drift in stochastic differential equations with arbitrary friction and diffusion in the Smoluchowski-Kramers limit
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Cited by in corpus (12)

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• Anisotropic thermophoresis
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• Non-Gaussian diffusion near surfaces
• Nonequilibrium fluctuation-induced Casimir pressures in liquid mixtures
• Thermally limited force microscopy on optically trapped single metallic nanoparticles
• Mode instabilities and dynamic patterns in a colony of self-propelled surfactant particles covering a thin liquid layer
• Different measures for characterizing the motion of molecules along a temperature gradient
• Controlling the shape of small clusters with and without macroscopic fields
• Temperature transitions and degeneracy in the control of small clusters with a macroscopic field