Polymer-induced entropic depletion potential

XZ Cao and H Merlitz and CX Wu and JU Sommer, PHYSICAL REVIEW E, 84, 041802 (2011).

DOI: 10.1103/PhysRevE.84.041802

We study the effective interactions between nanoparticles immersed in an athermal polymer solution using Molecular dynamics. The directly measured polymer-induced depletion forces are well described with a scaling model in which the attraction between particles is caused by the depletion of concentration blobs and thus independent of the length of the polymer chains. We find strong evidence for a repulsive barrier which arises when the distance between the particles is of the order of the correlation length of the solution and which can be interpreted as a packing effect of concentration blobs. Interestingly, the scaling picture can be extended into the regime in which higher virial coefficients of the polymer solution become relevant. We derive a universal relation between the attraction force at the particle contact, f(0), and the osmotic pressure Pi as f(0) similar to Pi(2/3), demonstrating its validity over a wide range of concentrations of the polymer solution.

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