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      Characterization, Mechanism and Kinetics of Phase-separation of Mixed Langmuir-Blodgett Films

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      Thesis_Qaqish_Final.pdf (7.262Mb)
      Date
      2009
      Author
      Qaqish, Shatha Eid
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
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      Abstract
      The phase – separation of mixed Langmuir-Blodgett (LB) monolayers was investigated using a combination of atomic force microscopy (AFM), X-ray photoelectron emission microscopy (X-PEEM) and confocal fluorescent microscopy measurements. Shapes of phase-separated domains that formed on solid substrate surfaces depended on a competition between line tension and dipole-dipole interactions. In the mixed LB film of arachidic acid (C19H39COOH) (C20) and perfluorotetradecanoic acid (C13F27COOH) (F14), the components phase – separated into elevated hexagonal domains of C20 surrounded by a continuous domain primarily consisting of F14. The underlying molecular arrangement of C20 was found to be an oblique packing. The domains in this system grew via Ostwald ripening and the kinetics of their growth was modeled by two–dimensional Lifshitz–Slyozov equation. In the stearic acid (C17H35COOH) (C18) and F14 mixed films, the C18 domains formed a linear pattern where the F14 molecules filled the areas in between the lines occupied by C18. For the mixed film of palmitic acid (C15H31COOH) (C16) and perfluorooctadecanoic acid (C17F35COOH) (F18), the surfactants phase–separated into elevated hexagonal domains with hairy extensions radiating from them. These domains were composed of F18 and surrounded by C16. Ostwald ripening was found to be the mechanism of domain growth. Phase – separation was controlled by different forces such as line tension and dipole interactions, as well as the diffusion of the molecules, solubility of the surfactant in the sub-phase, temperature and surface pressure. Simple mechanisms regarding phase –separation and pattern formation were discussed in these mixed systems. It was observed that all fatty acid / F14 systems in this study were immiscible at all molar fractions examined. The fatty acid / F18 systems were immiscible at short chains of fatty acids (myristic acid (C13H27COOH) C14, C16, C18), whereas at longer fatty acid chains (C20, C22 behenic acid (C21H43COOH)) the components of the mixed system became miscible. When perfluorocarboxylic acid chain combined with fatty acids, the domains changed from large hexagonal domains into narrow lines as the fatty acid chain decreased in length.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Chemistry
      Program
      Chemistry
      Supervisor
      Paige, Matthew
      Committee
      Baranski, Andrzej; Ward, Dale; Pan, Yuming; McDermott, Mark; Scott, Robert
      Copyright Date
      2009
      URI
      http://hdl.handle.net/10388/etd-04142009-124913
      Subject
      Monolayer
      Isotherm
      Adhesion
      Kinetics
      Compositional Mapping
      Fluorocarbon
      Hydrocarbon
      Mechansim
      Ostwald Ripening
      Lifshitz-Slyozov equation
      Diffusion
      Topography
      Atomic force microscopy
      Composition
      Phase-separation
      Langmuir-Blodgett
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