Thesis

Ion effects on stability of carbon nanotubes dispersions and complex formation in polar solvents

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Awarding institution
  • University of Strathclyde
  • Scottish Universities Physics Alliance.
Date of award
  • 2014
Thesis identifier
  • T13784
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Abstract
  • The focus of this work is the effects of ions on solute association processes in solution: complex formations of aromatic carboxylic acids with α-cyclodextrin and bundle formation of carbon nanotubes in their N-methylpyrrolidone based dispersions. The work has two distinct parts: cation effects and anion effects. In one part we explain experimentally observed difference between effects of sodium and potassium cations on interactions of aromatic carboxylic acids with α-cyclodextrin. To explain this difference, we propose a molecular mechanism, which we call "competition for the guest". According to this mechanism sodium ions interact with carboxylic group of aromatic carboxylic acid, which prevents the acid from the formation of a complex with cyclodextrin. Another manifestation of ion effects explored in this work is the impact of ions on the behaviour of benzoic acid at water/vapour interface. As a consequence of ion induced changes in hydration pattern, the molecule changes its orientation at the interface as well as its affinity to the interface. The results of the molecular dynamics simulations are compared to surface sensitive technique of X-ray photoemission spectroscopy. Another part of the work studies ion effects on the stability of carbon nanotube dispersions in N-methylpyrrolidone. By evidence of spectroscopy and transmission electron microscopy, it was found that inorganic ions significantly reduce stability of carbon nanotubes dispersions in N-methylpyrrolidone. Comparing the results to molecular dynamics simulations it was suggested that the reduction of stability takes place due to the formation of ion depletion areas around carbon nanotubes. These ion depletion areas increase the free energy of the interface between the tube and the salty N-methylpyrrolidone, forcing the carbon nanotubes to associate with each other, forming bundles and larger aggregates. Overall, this work is devoted to study of ion effects in aqueous and non-aqueous liquid media, using a combination of experimental and computational tools. Here we deepen the understanding of ion effects as a subtle balance of several pairwise interactions, which take place in liquid media containing both solutes and salts.
Resource Type
DOI
Date Created
  • 2014
Former identifier
  • 1036423

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