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    Multilayers in mixed perfluorocarbon-hydrocarbon surfactant films: Yes or no?

    Year: 2022

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 654, DEC 5

    Authors: Yeboah, Alfred; Muhammad, Shabaab; Yan, David; Singh, Srikant Kumar; Moreno, Beatriz; Paige, Matthew F.

    Organizations: Natural Sciences and Engineering Research Council (NSERC); University of Saskatchewan; Canada Foundation for Innovation (CFI); National Research Council (NRC); Canadian Institutes of Health Research (CIHR); Government of Saskatchewan; Natural Sciences and Engineering Research Council (NSERC); University of Saskatchewan; Canada Foundation for Innovation (CFI); NSERC; National Research Council (NRC); Canadian Institutes of Health Research (CIHR); Government of Saskatchewan; University of Saskatchewan

    Keywords: Monolayer; Multilayer; Langmuir Blodgett deposition; Perfluorocarbon; Hydrocarbon; Transfer efficiency

    Mixtures of perfluorotetradecanoic acid and arachidic acid form highly structured, phase-separated monolayers at the air-water interface, which can subsequently be deposited onto various solid substrates through Langmuir Blodgett deposition. While deposited monolayers in these systems are well-established and characterized, the ability to deposit multilayers remains entirely unexplored. The key complicating factor is that while pure fatty acids deposit with good efficiency in multilayers, pure perfluorinated fatty acid films do not, and the role this difference plays in mixed multilayer film deposition remains an unknown quantity. The transfer efficiency to solid substrates, resulting morphology and crystallographic structure of these mixed films has been assessed under a variety of conditions to evaluate if and how multilayer films can be produced in these systems. Under typical conditions used for Langmuir Blodgett multilayer deposition, including deposition from pure water or Cd2+ (aq) enriched sub-phases, mixed multilayer films would not deposit with any substantial efficiency onto solid substrates. A combination of surface characterization techniques indicates traditional multiple pass Langmuir Blodgett deposition (Y-type films) at the air-water interface results in repeated deposition and removal of the perfluorocarbon component of the mixed films with successive up-strokes and down-strokes, respectively. The inability to deposit mixed multilayer films using this approach appears to be an implication of the weak adhesion between putative layers of perfluorocarbon, and the ability of the hydrogenated fatty acid to fill in void regions left by stripping of the weakly adhered perfluorocarbon off the hydrophilic substrate.
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