Morphological and Interaction Characteristics of Surface‐Active Ionic Liquids and Palmitic Acid in Mixed Monolayers

A series of water soluble, surface‐active ionic liquids (SAILs), namely, 1‐alkyl‐3‐methyl imidazolium chlorides ([C n ‐ mim ]Cl) and their mixtures with palmitic acid (PA) are investigated in Langmuir monolayers and Langmuir–Blodgett films. It is inferred from the surface pressure‐area isotherms that C 16 ‐ mim ‐IL mixes non‐ideally with PA and stabilizes the binary mixed films. In addition, the residence of mim ‐IL at the water surface is enhanced as a function of the increasing alkyl side chain length. Generally, the compressional moduli values decrease upon increasing the content of the mim ‐ILs over a wide range of compositions. Furthermore, film relaxation measurements indicate that the IL component is selectively excluded from the mixed films upon achieving a certain target pressure. Brewster angle microscope images demonstrate minimal changes on the PA domains in the presence of either C 4 ‐ and C 8 ‐ mim ‐ILs, whereas presence of the hexadecyl counterpart results in the formation of condensed sheets. Atomic force microscopy imaging of deposited films show the formation of propeller‐like aggregates when C 8 ‐ or C 16 ‐ mim ‐IL is present in the mixed films.