Thermophoretic Random Walks and Enhancement of Diffusion

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The contribution of the stochastic thermodiffusion to the diffusion enhancement is studied. The thermodiffusion of particles suspended in a liquid may hold place when the spontaneous endo- or exothermal nanoscale events similar to elementary acts of enzymatic reactions occur as the random series in the space and time. In these events, the energy can be emitted or absorbed at nanoscale during few to hundreds of picoseconds. It may cause local spontaneous temperature spikes spreading quickly in the space and decaying with time. The random local temperature spikes create local transient temperature gradients, where thermodiffusion of the molecules and particles holds place as well as the change in the physical properties of the suspending medium due to heating. These thermodiffusion random walks may appear as the enhanced usual Stokes–Einstein diffusion when the energy absorption/generation is high enough. The evaluated relative contribution of the mentioned effect to the molecular mobility is shown to be in agreement with experimental data on enzymatic reactions from the literature.