Molecular simulation study on the colloidal suspension within dilute fibrous media: The effect of particle concentration
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Molecular Simulation Study on the Colloidal Suspension Within Dilute Fibrous Media: The Effect of Particle Concentration on Partitioning Myung-Suk Chun ~ and Chunggi Baig Complex Fluids and Membrane Lab, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650~ South Korea (Received 2 April 2001 . accepted 24 .hdy 2001)
Abstract-We investigated the molecular simulations based on the Gibbs ensemble Monte Carlo method, ~.hich was previously applied to the colloidal su@ensions confined with a narrow D-)re. [he long-range electrostatic interactions between the particle and the adjacent fiber and k~tween pairs of particles are evaluated by.'adopting the earlier methods. For uncharged cases, the partition coefficient with non-diltlte partieIe concentration decreases with increases in the ratio of particle radius to fiber radius. For charged systems with constant surface charges of both the particle and the tiber, the electrostatic interactions result in a diflkrcmt behavior according to the variations of particle concentration. Note that the particle concenu'ation is associated with the e]}~zets of steric exclusion as well as particle-particle interaction. B) developing an efl~ctive adjusting trial, the particle concentration in the bulk region has been kept as a constant during the simulation. The predicted density profiles of colloids around a fiber indicate that. whether the particles are uncharged or charged, the particle-particle interaction play's a significant rote, Key words: Gibbs Ensemble Monte Carlo. Electrostatic Interaction, Equilibrium Partkioning, Fibrous Media, Radial Density Pmfile
INTRODUCTION
cles were obtained by emplwing both density functional theory and grand canonical Monte Carlo simulations {Fanti and Glandt, 1990a, b]. Applying a supeqmsition approximation to the density profile of particles around a single fiber, the partition coefficient at low to moderate fiber volume fractions is given by
Colloidal suspensions confined with solid walls are a frequently encountered situation, althou~ most studies have focused on colloids in unbounded spaces [karson, 19991. Among the confined systems, the fibrous media have relevance to many processes such as gel chromatography, gel electrophoresis, fibrous membranes, controlled drug delivery, and many kinds of therapeutic or physiological devices [Johnson et al., 1995; Tong and Ande~.'son, 19%1. One of the basic properties of colloidal suspension within fibrous media is the concen~ation distribution between the fiber matrices and the bulk. This static property is characterized by the partition coefficient [Buck et at., 2001], which is necessary to the estimation of dynamic properties. Over 40 years ago, the earliest study provided a theoretical result of the equilibrium partitioning of a spherical particle in a randomly oriented array of straight, cylindrical fibers tO,ton, 1958], Statistically considering only steric interactions with infinitely dilute system, the partition coefficient K defined by the ratio of the average part
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