COLL 514 |
| Jianzhong Wu, Department of Chemical and Environmental Engineering, Department of Chemical and Environmental Engineering, University of California, A317 Bourns Hall, Riverside, CA 92521 |
| Electrostatics is fundamental to a broad variety of phenomena in surface chemistry ranging from traditional topics like colloidal stability, eletrocapillarity, and electrophoresis to properties and functions of biomacromolecules that are of great interest in modern biotechnology. The conventional approaches for quantitative interpretation of these phenomena are based on the Poisson-Boltzmann equation that ignores the molecular identities of solvent and salt ions as well as various non-bonded intermolecular forces that often interfere with the electrostatic phenomena. In this work, we explore the limits of the Poisson-Boltzmann equation by extensive comparison with the results from Monte Carlo simulations, density-functional theory, and experimental data. While the Poisson-Boltzmann equation is adequate for the long-range behavior of electrostatic phenomena in monovalent electrolyte solutions, it is inappropriate for most systems containing multivalent ions and fails to predict a plethora of electrostatic phenomena including macroion charge inversion, attraction between similar charged species, the structural ordering of charged particles in a crowded environment. We find that charge inversion is commonplace for macroions dispersed in an electrolyte solution containing multivalent counterions and the magnitude of inversion increases with the counterion size and concentration or the charge density of macroion surface. In direct contrast to the prediction of the Poisson-Boltzmann equation, calculations from Monte Carlo simulation and density functional theory both indicate the possibility of electrostatic attraction between similarly charged macroions and the attractive force is intensified by considering the surface charge distributions. Both the density functional theory and simulation results contradict the monotonic behavior of the macroion zeta potential predicted by the Poisson-Boltzmann theory. Similar results are observed by direct comparison of theoretical predictions with experimental data. |
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Symposium in Memory of Arthur W. Adamson
2:00 PM-5:20 PM, Thursday, April 1, 2004 Marriott -- Orange County 3, Oral
Division of Colloid and Surface Chemistry |