Masters Theses

Date of Award

8-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Hank D. Cochran

Committee Members

Shengting Cui, David Keffer, Mary Leitnaker

Abstract

This thesis discusses the molecular dynamics simulation to determine the density distribution and diffusion coefficient of aqueous electrolytes (CaCl2, NaF, NaCl, NaBr, NaI, KCl, CsCl, RbCl) within silica nanochannels at 298K. An atomistic wall model, charged Lennard-Jones models for the ions, and the SPC/E model for water have been used. The effect of different channel radius and wall charges on divalent CaCl2 electrolytes solutions is discussed in comparison with the previously studied behavior of monovalent NaCl solutions. The comparison of (NaF, NaCl, NaBr, NaI) aqueous solutions in 1.0 nm nanochannel reveals the effects of different anion sizes. Likewise, the comparison of (KCl, NaCl, CsCl, RbCl) aqueous solutions shows the effects of different cation sizes. The effects of ions size were seen to be small compared with the effects of doubling the cation charge. The calculations demonstrate that charges on the wall surface exert an influence on the density distribution of water molecules and calcium ions. Divalent calcium ions also display a different diffusion characteristic from the Fickian behavior of the monovalent cations, in which the mean square displacement of calcium ions is proportional to the square root of time rather than to the first power of time.

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