Critical Depletion

Abstract

Depletion interactions and the critical Casimir effect are usually regarded as distinct phenomena in colloidal suspensions. By experimentally investigating how the Asakura-Oosawa picture, appropriate for a weakly correlated depletant, is modified when critical correlations develop within the depletion agent, we conversely show that the former merges continuously into the latter, leading to a distinctive scaling behavior solely dictated by the depletant correlation length. A model based on density functional theory provides a microscopic understanding of the phenomenon and properly accounts for the observed trends.