Evacuation of Counteranions from Langmuir Monolayers of Double-Tailed Quaternary Ammonium Ions into Subphase at High Surface Pressures as Studied by Total Reflection X-ray Absorption Spectrometry

Abstract

Total reflection X-ray absorption fine structure (TR-XAFS) has been utilized for the detailed analyses of the surface aggregation of double-tailed quaternary ammonium ion bromides. TR-XAFS at the Br K-edge gives us information on the population of Br -just below the subphase surface as well as its local structure. The spectra indicate that Br -is almost completely hydrated, even when it is attracted by the compressed monolayer. In addition, the signal intensities obtained for the monolayers of the ammonium amphiphiles with different hydrocarbon chain lengths suggest that the correction for the attenuation of X-rays due to the absorption by the hydrocarbon layer is necessary to obtain a reliable population of Br -on the subphase surface. The correction of the attenuation reveals that the population of Br -is lower than that predicted on the basis of the electrostatic attraction, and that this deviation becomes larger as the monolayer is compressed. These findings can be explained by the submergence of Br -into the subphase when the amphiphiles are substantially in contact with each other upon the compression of the monolayer. This consideration is also supported by the pressure-molecular area (π-A) isotherms.

Eutectic Transition of Local Structure for Bromide Ion in Bulk and on Surface of Doped Ice

“…Also, revealing the local structures of ions below and above t eu should allow the discussion of a phase transition on a molecular basis. We have studied the local structures of Br − by X-ray absorption fine structure (XAFS) in an anion-exchange resin, , on a cationic micellar surface, , on a cationic Langmuir monolayer, , and in concentrated aqueous polyethyleneglycol, , and have revealed that hydrated Br − can release some water molecules from its first hydration shell under some conditions. When the temperature of salt-doped ice is raised above the eutectic temperature ( t eu ) of the system, a liquid phase starts to emerge.…”

Lubrication by Adsorption Films of Hydrophilic Amine-based Protic Ionic Liquids: Effect of Anion Species

“…Regardless of the structure of the anions (i.e., malate, lactate, methoxyacetate, and acetate) , the molecular occupied areas were calculated to be approximately 1.2 nm 2 at 1.0 wt％. This value is comparable to that estimated for a liquid expansion film of a quaternary ammonium-type compound with a dissociated anion 19) . It appears that the structural difference in the anion imposed a less prominent effect on the adsorption than that in the cation 14) when the surface charge state of the metal oxide was negative.…”

Adsorption of Hydrophilic Amine-Based Protic Ionic Liquids on Iron-Based Substrates

“…The area was calculated as approximately 1.2 nm 2 for TEtOHA Lactate the sample with the highest adsorption mass . It has been reported that a quaternary ammo-nium-type compound with a dissociated anion formed a liquid expansion film from a molecular area of 0.8 nm 2 during compression at the air/water interface 18 . The occupied area we estimated in this study was close to this molecular area.…”