Salt dependent stability of stearic acid Langmuir-Blodgett films exposed to aqueous electrolytes

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Abstract

We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the stability and wettability of Langmuir–Blodgett (LB) monolayers of stearic acid on silica substrates, upon drying and exposure to aqueous solutions of varying salinity. The influences of Ca2+ and Na+ ions are compared by varying their concentrations, both in the subphase before the LB transfer, and in the droplets to which the dried LB layers are exposed. Ca2+ ions in the subphase are found to enhance the stability, leading to contact angles up to 100°, as compared to less than 5° for Na+. Consistent with the macroscopic wettability, AFM images show almost intact films with few holes exposing bare substrate when prepared in the presence of Ca2+, while subphases containing Na+ result in large areas of bare substrate after exposure to aqueous drops. The observations on varying the composition of the droplets corroborate the stabilizing effect of Ca2+. We attribute these findings to the cation-bridging ability of Ca2+ ions, which can bind the negatively charged stearate groups to the negatively charged substrates. We discuss the relevance of our findings in the context of enhanced oil recovery
Original languageEnglish
Pages (from-to)5150-5159
JournalLangmuir
Volume29
Issue number17
DOIs
Publication statusPublished - 2013

Keywords

  • METIS-300699
  • IR-88604

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