FTIR studies on Langmuir–Blodgett (LB) films of amphiphile with Schiff base moiety as headgroup

In the present study, an amphiphile 2,4-dihydroxy-N-octadecylbenzylideneamine with novel structure was designed and synthesized. The aggregation structure of this amphiphile in LB films was investigated through FTIR spectroscopic techniques. The surface pressure-dependent infrared spectra of LB films have revealed some important insights on the bonded properties of the headgroup for this amphiphile. It was found that the types of H-bond formed among/between the Schiff base headgroups are determined by the deposition pressure. Intermolecular H-bond is prominent in Z-type LB film deposited at a surface pressure of ≤30 mN/m, while intramolecular H-bond formed between 2-hydroxyl group and the azomethine nitrogen is more favorable in Y-type LB film fabricated at a surface pressure of ≥40 mN/m. The variable-temperature infrared spectra of LB films further provide powerful evidence for the conversion between intermolecular and intramolecular H-bond, depending on the surface pressure.