Investigations of Phase Instabilities and Many---Body Physics in Charge---Stabilized Colloidal Dispersions.

摘要

Neutron scattering experiments involving low ionic strength polyelectrolyte solutions in the absence of added salt show a steep upturn in scattering profile in the low angle limit. This steep upturn at low q appears to be a general feature for highly-charged systems, such as polyelectrolytes, colloids, and vesicles, and may be the result of fluctuations around an unrealized critical point. We investigate a toy model of a solution of charged colloids in the restricted primitive model with multiple geometries. Linear mean-field analysis of the salt-free system indicates a region of instability, though this region may exist beyond the realm of validity of the linear theory. Nonlinear effects absent from the linear theory result in the condensation of counterions to the surface of the macroion, possibly keeping the system in a regime where linearization is appropriate as well as providing a mechanism for correlations induced by fluctuations of the surface charge density. In order to investigate this system further we implement Monte Carlo simulations to calculate the full interactions beyond the linear theory. The algorithm developed by Wang and Landau is used to calculate the thermodynamic properties of colloidal systems and to characterize the region of phase instability.