We consider placing a rigid spherical particle into a binary fluid mixture in the homogeneous phase near the demixing critical point. The particle surface is assumed to have a short-range interaction with each mixture component and to attract one component more than the other. Owing to large osmotic susceptibility, the adsorption layer, where the preferred component is more concentrated, can be of significant thickness. This causes a particle motion under an imposed composition gradient. Thus, diffusiophoresis emerges from a mechanism which has not been considered so far. We calculate how the mobility depends on the temperature and particle size.
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