Computer simulation study on the concentration distribution of spherical colloids within confined spaces of well-defined pores

Abstract

Aside from the virial expansion and density functional methods, theoretical results on the concentration partitioning behavior for charged colloids within cylindrical pores have not been presented so far. With the increase of relative solute size as well as solute concentration, however, the approximate analytic methods have proven to be unreliable. A suitable Monte Carlo simulation, which is proved as a rigorous technique for concentrated colloids, has been applied in the present study. The concentration profiles within the pore representing the effects of solute concentration as well as solution ionic strength are obtained via a stochastic process, from which the partition coefficient is estimated. Previously developed analyses on the linearized Poisson-Boltzmann (P-B) equation are employed for the estimation of long-range electrostatic interaction. Both the singularity method and the analytical solution with series representation properly determine respective interaction energies between pairs of solute particles and between the solute particle and the pore wall. The effect of solute-solute and solute-wall interactions associated with repulsive energy is presented on the partitioning of colloids. Simulation results show that the partition coefficient is evidently enhanced when no particle-wall interaction exists. Hindered diffusion can be predicted by the simplifying assumption of the centerline approximation analogy, where a dependence on the solute concentration becomes greater as the solution ionic strength decreases.