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      Physical Chemistry of Gemini Surfactant Monolayers

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      REHMAN-DISSERTATION-2020.pdf (7.388Mb)
      Date
      2020-08-13
      Author
      Rehman, Jeveria
      ORCID
      0000-0002-6903-7341
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
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      Abstract
      The objective of this Ph.D. thesis research is to explore the effect of cation (Na+, Ca2+, and Fe3+) binding on monolayers comprised of two newly synthesized anionic gemini surfactants (Ace(n)-2-Ace(n), n = 11, 17; Figure 1) at the air-water and air-solid interfaces. The study was further aimed at exploring the miscibility and interactions of the Ace(n)-2-Ace(n) surfactants with perfluorotetradecanoic acid (C13F27COOH; PF) in monolayers. A combination of monolayer characterization methods, including surface pressure-area isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) were used to explore the effect of ion-binding and mixing on the thermodynamics of mixing and the morphology of the monolayer films. Figure 1: Chemical structure of Ace(n)-2-Ace(n) (n = 11,17). Ace(n)-2-Ace(n) monolayers exhibited significant expansion with Na+ and Ca2+ in the sub-phase, while with Fe3+ in the sub-phase, compressed films were observed. Apparent association constants (Kapp) for Ace(n)-2-Ace(n) were smaller than the comparator phospholipids systems reported in the literature, and gemini-cation binding stoichiometries of 2:1 and 1:1 for Ca2+ and Na+ respectively were found. Multimolecular aggregates of Ace(n)-2-Ace(n) bonded to cations were observed in BAM and AFM images. Results were discussed in the context of grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) measurements performed by other members of our research group. For the Ace(n)-2-Ace(n)-PF mixed monolayers, thermodynamic, morphological and X-ray scattering studies indicated that PF-Ace(12)-2-Ace(12) mixed films were miscible over a wide range of compositions at lower surface pressures. For PF-Ace(18)-2-Ace(18) mixed films, phase separation was detected at all surface pressures. GIXD and XR studies revealed that Ace(n)-2-Ace(n) forms amorphous, disordered monolayers at the air-water interface while PF forms a crystalline lattice with hexagonal symmetry. Overall the research in this thesis provides insight into fundamental interactions of this new class of gemini surfactants with metal cations in monolayers and an understanding of the physical and chemical factors that control mixing behavior in PF-Ace(n)-2-Ace(n) mixed monolayers. Future areas of research that are suggested by this work include developing new approaches for quantifying the extent of surfactant binding to metal ions in the monolayers and clarifying the precise nature of binding between Ace(n)-2-Ace(n) and metal cations.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Chemistry
      Program
      Chemistry
      Supervisor
      Paige, Matthew
      Committee
      Wilson, Lee; Sanders, David; Nemati, Mehdi; Burgess, Ian
      Copyright Date
      July 2020
      URI
      http://hdl.handle.net/10388/12960
      Subject
      Gemini surfactant, BAM, Surface Potential, Monolayers, Isotherms.
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