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.

References in corpus (2)

• State-dependent diffusion: thermodynamic consistency and its path integral formulation
• Characterizing Potentials by a Generalized Boltzmann Factor

Cited by in corpus (6)

• Colloidal Motion under the Action of a Thermophoretic Force
• Non-Gaussian diffusion near surfaces
• Thermally limited force microscopy on optically trapped single metallic nanoparticles
• Different measures for characterizing the motion of molecules along a temperature gradient
• Temperature transitions and degeneracy in the control of small clusters with a macroscopic field
• Controlling the shape of small clusters with and without macroscopic fields