Wall–particle interactions and depletion forces in narrow slits

•Effective force induced by confined colloidal suspensions and mixtures is addressed.•Depletion, accumulation, bridging and repulsion through attraction effects•Confinement strongly affects the phase behavior and structure of suspensions.•Capillarity effects on melting, freezing, condensation and evaporation•Internal morphology of soft nanoparticles changes under tight confinement.

Understanding the depletion forces in monocomponent and multicomponent colloidal suspensions within confined conditions has become a topic of increasing interest over the last years in Soft Matter Physics since they are involved in many biological and technological applications. In this review, we discuss the equilibrium and coexistence properties of colloids, polymers, and colloid–polymer mixtures confined between two parallel plates (slit pore geometry), and deal with the effective surface–surface interactions induced by the suspension. Theoretical and experimental results clearly show that, under confinement, the microstructure (ordering) of the suspension, the phase coexistence, the internal architecture of the particles (for the case of polymers and similar kind of soft colloids) and the effective depletion interaction arising in colloid–polymer mixtures strongly differ from the ones observed in free bulk suspensions. On the other hand, effective wall–wall interactions are also notably influenced by the nature of the particle–particle and particle–wall interactions, and by the particular internal morphology of the nanoparticles.

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