1201.0810 (Chi-Lun Lee)

Energy and entropy effects of counterions in salt-free colloidal
solutions    [PDF]

Chi-Lun Lee

We use a shell model to study the counterion interactions in a colloidal
solution. In this shell model, the counterions are restricted to move inside a
spherical region about their host colloidal particle. In particular, we apply
Monte Carlo simulations to derive the energy and entropy contributions of the
effective colloidal interaction. Our result reveals an attractive electrostatic
energy, which is overpowered by the osmotic repulsion among the counterions, as
the latter can be well estimated by an ideal-gas approximation. We also provide
an optional algorithm that enables counterion mixing between the two counterion
clouds even when the clouds do not overlap. The residual mixing entropy of
counterions gives a reduction in free energy that is comparable to the thermal
fluctuation, suggesting a possible attractive mechanism between the colloidal
particles under non-equilibrium condition.

View original: http://arxiv.org/abs/1201.0810