Mixing Behavior in Binary Anionic Gemini Surfactant–Perfluorinated Fatty Acid Langmuir Monolayers

Abstract

The miscibility and film structure of mixed Langmuir monolayer films composed of an anionic gemini N,N,N',N'-dialkyl-N,N'-diacetate ethylenediamine surfactant (Ace(12)-2-Ace(12)) with perfluorotetradecanoic acid (CFCOOH; PF) have been investigated using a variety of thermodynamic and structural characterization methods. The two film components were found to be miscible in monolayers at the air-water interface over a range of compositions and at all but the lowest surface pressures, with attractive interactions occurring between the two components. While pure PF monolayers formed crystalline lattices with hexagonal symmetry and with the surfactant tails oriented normal to the underlying water subphase, the pure gemini surfactant formed amorphous films with little tendency to orient at the subphase. In mixed films with mole ratios of PF:Ace(12)-2-Ace(12) < 2.5, the miscibility of the two components resulted in a nearly complete loss of crystallinity of the PF, though films at higher mole fractions of PF showed some residual crystallinity, albeit with lattice structures that were significantly different from that of pure PF. Miscibility and film structure in this mixed system are discussed in comparison with other mixed gemini surfactant systems in the literature as well as binary mixtures of phospholipids or monomeric fatty acids with PF.

Iron Binding in an Ethylenediaminetetracetic Acid‐Based Gemini Surfactant Monolayer Film

“…Resulting electron density profiles were fit using a standard two‐slab model in which one slab of electron density corresponds to the monolayer head group and the second slab to the tail group; fitting data are summarized in Table 3. The overall film thickness and slab‐fitting results for the monolayer on pure water were comparable with the previously measured values for Ace(18)‐2‐Ace(18), and the tail layer length was greater than that of the shorter Ace(12)‐2‐Ace(12) surfactant, as expected (Rehman et al, 2017b, 2019). The key observation from film thickness measurements was that a small (~ 4 Å) but significant decrease in tail layer length was observed when switching to an Fe 3+ ‐enriched subphase.…”

Thermodynamic Behaviour of Mixed Films of an Unsaturated and a Saturated Polar Lipid. (Oleic Acid-Stearic Acid and POPC-DPPC)

“…One of the main aspects of these mixtures is the miscibility and phase separation. Recent articles on mixed fatty acids systems are those of [23][24][25][26][27][28][29][30][31][32]. Furthermore, since fatty acids or phospholipids usually present unsaturations in the hydrocarbon chains, the study of mixtures of saturated and unsaturated compounds is of interest.…”

Pattern Formation in Phase-Separated Langmuir and Langmuir Monolayer Films

“…Perfluorinated surfactant monolayers are particularly well-suited to diffraction experiments because of their large electron density and, in the case of perfluorinated fatty acids, of the nature of their crystalline packing and reflection degeneracy. GIXD experiments from a perfluorotetradecanoic acid typically shows a single, strong diffraction peak in a GIXD contour plot ( q z intensity vs q xy ), indicating a normal orientation of the perfluorinated molecules to the water subphase and a hexagonal lattice packing. ,,, For hydrocarbon fatty acids, both in-plane and out-of-plane scattering can be obtained, which shows that the hydrocarbon molecules are tilted to the water subphase at various angles depending on the surface pressure and composition in the subphase . On the other hand, in the case of semifluorinated alkane (SFA), two Brag Peaks can be observed at q xy , which were associated with hexagonal packing of the fluorocarbon and hydrocarbon blocks, respectively .…”

“…Images were collected at T = 21 °C. Reprinted with permission from ref . Copyright 2017 American Chemical Society.…”

“…To date, we have investigated mixing for two gemini variants, Ace(12)-2-Ace (12) and Ace(18)-2-Ace (18), with C13F. 37,24 For the former, the surfactant tail lengths were considerably shorter than the fatty acids we studied previously and thus we hypothesized that Ace(12)-2-Ace( 12) would be miscible with C13F; likewise, it was hypothesized that miscibility would decrease with the longer tail chain in Ace(18)-2-Ace (18).…”