Using a lattice self-consistent field (SCF) theory and the corresponding lattice Monte Carlo (MC) simulations combined with our recently proposed Z method (Zhang, P.; Wang, Q. Soft Matter, 2015, 11, 862), we examined homopolymer solutions confined between two parallel and nonabsorbing surfaces and in equilibrium with a bulk solution, and accurately calculated the effective interaction between the two surfaces. Close to the critical point of the solution, we found for the first time, by using the SCF theory, the Casimir effect with long-range attractive intersurface potential W&lt;0 extending to D/Re≈10, where D denotes the intersurface separation and Re the root-mean-square chain end-to-end distance in the bulk solution. On the other hand, by directly comparing our MC results with SCF predictions based on the same model system, we were able to quantitatively and unambiguously distinguish the mean-field and the fluctuation contributions to W, and found for the first time the fluctuation-induced repulsion W&gt;0 between the two confining surfaces at intermediate D≈Re (i.e., the anti-Casimir effect) predicted by Semenov and Obukhov (Obukhov, S. P.; Semenov, A. N. Phys. Rev. Lett. 2005, 95, 038305), which is about one order of magnitude stronger than that due solely to the finite chain length as predicted by the SCF theory. The repulsion strength decreases with decreasing solvent quality and vanishes near the critical point.

Interactions between colloidal particles mediated by nonadsorbing polymers: Casimir and anti-Casimir effects

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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