A new way of measuring Soret coefficient $S_T$, ratio of thermal diffusion and diffusion coefficient, on a single particle in an aqueous solution is presented in the master's thesis. Heating and cooling of a microcapillary on the edges gives a constant value of temperature gradient along the whole measured area, allowing observation of the same sample at different temperatures. It turns out that optical tweezers do not allow measurements of small enough forces, caused by thermophoresis, so the emphasis is on particle drift velocity measurement. From acquired velocities, $S_T$ can be calculated and by measurements at different temperatures it is presented, that thermophoresis is dependent on absolute temperature of the environment.
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