Universality of Entropic Surface Segregation from Athermal Polymer Blends Due to Conformational Asymmetry

We
reexamine off-lattice Monte Carlo simulations for athermal blends
of stiff and flexible polymers next to a hard wall. The original simulations
[Kumar et al. J. Chem. Phys. 1995, 103, 10332], which were supported by wall-PRISM calculations,
predicted a short-range preference for the stiff polymers at the wall,
which contradicts experiments as well as alternative calculations.
On this basis, Kumar et al. asserted that the true entropic preference
in the experiments was masked by enthalpic interactions and that the
other calculations were incorrect because they did not account for
local packing effects at the wall. However, with vastly improved equilibration
and statistics, we now find that the simulations actually predict
a long-range surface preference for the flexible polymers, which resolves
a controversy that has existed for over 25 years. Furthermore, we
show that the excess of flexible polymer adopts a universal concentration
profile, as predicted by mean-field theory [Wu et al. J. Chem.
Phys. 1996, 104, 6387].