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Many-body depletion forces of colloids in a polydisperse polymer dispersant in the long-chain limit

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Abstract

We study a system of spherical non-adsorbing particles immersed in a polydisperse polymer fluid. We derive an analytic expression for the many-body depletion interactions between the colloidal particles in the limit of very long chains. We argue that this expression is essentially exact for long chains and justify this using explicit simulations. In this way we are able to elucidate the profound effect of many-body interactions on the particle thermodynamics. We show that using truncated 2-body depletion interactions leads to strong particle segregation, while the complete many-body description predicts that the total depletion force becomes weak so that the system approximates one which interacts via a so-called Kac potential. This implies that the depletion interactions can be described using mean-field theory. We show that many-body effects cause a significant contraction of the 2-phase region of the particle dispersion. We also investigate the system approaching the (tricritical) θ point, which terminates the line of first-order critical points of the polymer dispersion in a poor solvent and show that many-body effects suppress particle phase transitions.

Graphical abstract: Many-body depletion forces of colloids in a polydisperse polymer dispersant in the long-chain limit

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Publication details

The article was received on 26 Mar 2018, accepted on 30 Jul 2018 and first published on 31 Jul 2018


Article type: Paper
DOI: 10.1039/C8SM00631H
Citation: Soft Matter, 2018, Advance Article
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    Many-body depletion forces of colloids in a polydisperse polymer dispersant in the long-chain limit

    H. S. Nguyen, J. Forsman and C. E. Woodward, Soft Matter, 2018, Advance Article , DOI: 10.1039/C8SM00631H

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