Order-disorder transitions in Langmuir-Blodgett films. IV. Structure of [F(CF₂)₈(CH₂)₁₀COO^-] ₂ Cd²⁺ multilayers at ambient and elevated temperatures

Langmuir-Blodgett multilayered (6-12) films of a semifluorinated fatty acid, F(CF2)8(CH2)10COOH, have been deposited on transmission and reflection substrates and investigated using polarized infrared (IR) spectroscopy. The spectra revealed that the cadmium salt of this fatty acid was transferred and not the acid itself. Unlike its hydrocarbon analog, [F(CF2)8(CH2)10 COO-]2 Cd2+ is not oriented normal to the surface but is inclined due to the packing constraints dictated by the considerably larger cross section of the fluorocarbon part of the molecule. At elevated temperatures, the orientation of the fluorocarbon chain is observed to change and this has been attributed to disordered conformations preferentially introduced in the hydrocarbon portion of the molecule due to its inherent flexibility relative to the rigid fluorocarbon helix. © 1989 American Institute of Physics.