The effect of fluorination on the surface chemistry of adsorbate-metal systems
Meyers, Jerry Michael
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Permalink
https://hdl.handle.net/2142/22821
Description
Title
The effect of fluorination on the surface chemistry of adsorbate-metal systems
Author(s)
Meyers, Jerry Michael
Issue Date
1995
Doctoral Committee Chair(s)
Gellman, A.J.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Ultra-high vacuum surface techniques are used to determine the effect of substituents (mainly fluorine) on the surface chemistry of several adsorbate-metal systems. In the first system, the effect of two substituent groups ($-$CH$\sb3$ and $-$F) on the kinetics of the phenyl coupling reaction on the Cu(111) surface has been studied. The electron withdrawing fluorine group in the meta or para position of the phenyl ring was shown to lower the activation barrier to phenyl coupling while fluorine in the ortho position raised the barrier. The electron donating methyl group in the meta position was found to raise the activation barrier. From the activation barriers and preexponentials, reaction rate constants were calculated and used to construct a linear free energy relationship or Hammett plot. From this plot the reaction constant was found to be $6.0\pm3.3.$ The positive value of the reaction constant indicates that the transition state of the phenyl coupling reaction is electron rich with respect to the initial state.
In the second system, we have used small fluorinated ethers as models for perfluoropolyalkylether (PFPAE) lubricants to determine the effect of fluorination on the surface chemistry of the alkylethers adsorbed on the Cu(111) surface, the Al(110) surface and an Al$\sb2$O$\sb3$ surface. On the Cu(111) and Al(110) surface, none of the ethers studied (either hydrogenated or fluorinated) were found to decompose. Similarly, upon fluorination of the alkylethers, the adsorbate-metal bond was weakened by 5-7 kcal/mole. On Cu(111), the interaction parameters $(\alpha)$ for the hydrogenated ethers were found to have repulsive adsorbate-adsorbate interactions, while the fluorinated ethers were found to have attractive adsorbate-adsorbate interactions. On the Al(110) surface, the hydrogenated ethers were found to have extremely repulsive adsorbate-adsorbate interactions, while the perfluorinated ethers only exhibited mildly repulsive interactions. On the Al$\sb2$O$\sb3$ surface, TPD measurements determined that the fluorinated ethers bond weakly to the Al$\sb2$O$\sb3$ surface and possess mildly repulsive adsorbate-adsorbate interactions.
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