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Effects of Cu(II) on the Formation and Orientation of an Arachidic Acid Langmuir–Blodgett Film

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journal contribution
posted on 12.02.2019, 00:00 by Briana A. Capistran, G. J. Blanchard
The influence of the copper­(II) ion on the formation, morphology, and organization of an arachidic acid monolayer was investigated using Langmuir–Blodgett (LB) monolayers, Π–A isotherms, and Brewster angle microscopy (BAM). Our findings indicate that a Cu2+-complexed LB film exhibits an order that depends on the subphase pH, analogous to other metal ions. Yazdanian, M.; et al.Ionic Interactions of Fatty Acid Monolayers at the Air–Water Interface. Langmuir 1990, 6, 1093–1098.Kurnaz, M. L.; et al.Morphology of Microphase Separation in Arachidic Acid–Cadmium Arachidate Langmuir–Blodgett Multilayers. J. Phys. Chem. 1996, 100, 11113–11119.The metal ion facilitates the formation of solid-phase films at surface pressures as low as 5 mN/m. The films exhibit a rigid, ordered phase, evidenced by the absence of a collapse point and an increase in surface pressure rather than the typical sharp decrease in surface pressure, indicative of film failure. Amphiphile ionic charge vs pH (i.e., the extent of arachidic acid protonation) plays a role in the observed absence of collapse and the ability of the films to maintain order and cohesion at high surface pressures (ca. 65 mN/m). Additionally, film thickness data suggest that the incorporation of Cu2+ ions induces a change in orientation of the aliphatic chains of the amphiphiles and that amphiphile solubility in the subphase may play a role in the observed film behavior at low surface areas and high pH.