Theoretical modeling and computer simulation of irreversible adsorption processes
Abstract
The irreversible adsorption of large molecules such as proteins, latex, and colloidal particles from solution to solid surfaces plays an important role in a wide variety of practical problems. Despite this significance, the development of theoretical models for such processes is still in its infancy. A fundamental model which has been proposed for the irreversible, monolayer adsorption of large molecules is Random Sequential Adsorption (RSA). In RSA, hard-core particles are added sequentially to a surface in random positions subject to the constraint of no overlap. Once adsorbed, the particles neither diffuse on the surface nor desorb from it. RSA has been studied extensively using spherical particles and its predictions have been verified in experiments using approximately spherical proteins and latex colloids. However, no attempt had been made to incorporate the anisotropic effects associated with the adsorption of nonspherical molecules until recently. This work is devoted to the extension of RSA to describe adsorption processes involving large, nonspherical molecules. The effects of particle shape and elongation on the kinetics and surface-phase structure are investigated. Analytical equations for the low- and high-coverage kinetics are derived and the results are compared with computer simulation. Due to inherent difficulties in obtaining reliable data for the high-coverage regime from simulation, a new algorithm is developed which permits precise estimates of kinetic parameters using only a small fraction of the CPU time required by conventional methods. Using the results for the short- and long-time kinetics, approximate equations which accurately reproduce simulation data over the entire range of coverage are constructed. In order to determine the effect of surface diffusion on the adsorption kinetics and surface structure, the radial distribution function is calculated for surface phases produced in RSA and compared with that for equilibrium fluids at the same coverage. Finally, an RSA model which takes into account the changes in orientation of adsorbed particles with respect to the surface is proposed and simulation results are compared with those from experiments reported in the literature.
Degree
Ph.D.
Advisors
Talbot, Purdue University.
Subject Area
Chemical engineering
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