A molecular-dynamics simulation study of the effect of surface steps on alkane surface diffusion

Author

Shrijay Subramanian

Abstract

"This work uses Molecular-Dynamics simulations to study the behavior of three n-alkanes - n-butane, n-decane and n-hexadecane on two types of surfaces: flat Pt(lll) surface and stepped Pt(655) surface. The Anisotropic United Atom (AUA) model has been used to model the n-alkane molecules. The united atom-united atom, united atom-surface atom and surface atom-surface atom interactions were modeled using the Lennard Jones (12-6) potential.

On the flat surface, the diffusion is isotropic and two-dimensional. At lower temperatures, the primary modes for the surface diffusion mechanism are the rotational and translational modes. At higher temperatures, torsion and bending are also important. The diffusion energy barrier varies linearly with chain length and the diffusion coefficient decreases with chain length. The surface step influences the surface diffusion very strongly. The potential field becomes anisotropic and surface diffusion is mostly one-dimensional along the step edge. The molecules seldom moved away from the step and in the event they do, they quickly get back to the step. The extent of the influence of the step is dependent on the chain length. The stepped surface also has a profound influence on the conformation of the molecules and favors the trans-conformation. It aids conformational changes in the molecules at higher temperatures. The diffusion energy barrier for the n-alkanes on the stepped surface is found to increase linearly with chain length. No jumps were observed from the lower terrace to the upper terrace of the step for any of the alkanes in spite of a three fold increase in temperature. Static calculations were performed to independently verify the diffusion energy barriers for each of the alkanes"--Abstract, page iii.

Advisor(s)

Wang, Jee C.

Committee Member(s)

Neogi, P. (Partho), 1951-
Blum, Frank D.

Department(s)

Chemical and Biochemical Engineering

Degree Name

M.S. in Chemical Engineering

Sponsor(s)

University of Missouri--Rolla. Department of Chemical Engineering
National Science Foundation (U.S.)

Publisher

University of Missouri--Rolla

Publication Date

Fall 2003

Pagination

xi, 67 pages

Note about bibliography

Includes bibliographical references (pages 64-66).

Rights

© 2003 Shrijay Subramanian, All rights reserved.

Document Type

Thesis - Restricted Access

File Type

text

Language

English

Subject Headings

Molecular dynamics -- Simulation methods
Alkanes
Surface chemistry

Diffusion

Thesis Number

T 8459

Print OCLC #

55496145

Electronic OCLC #

933758648

Link to Catalog Record

Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.

Recommended Citation

Subramanian, Shrijay, "A molecular-dynamics simulation study of the effect of surface steps on alkane surface diffusion" (2003). Masters Theses. 4429.
https://scholarsmine.mst.edu/masters_theses/4429